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Bibliography on: Reynolds Number

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ESP: PubMed Auto Bibliography 03 Dec 2020 at 01:32 Created: 

Reynolds Number

It is well known that relative size greatly affects how organisms interact with the world. Less well known, at least among biologists, is that at sufficiently small sizes, mechanical interaction with the environment becomes difficult and then virtually impossible. In fluid dynamics, an important dimensionless parameter is the Reynolds Number (abbreviated Re), which is the ratio of inertial to viscous forces affecting the movement of objects in a fluid medium (or the movement of a fluid in a pipe). Since Re is determined mainly by the size of the object (pipe) and the properties (density and viscosity) of the fluid, organisms of different sizes exhibit significantly different Re values when moving through air or water. A fish, swimming at a high ratio of inertial to viscous forces, gives a flick of its tail and then glides for several body lengths. A bacterium, "swimming" in an environment dominated by viscosity, possesses virtually no inertia. When the bacterium stops moving its flagellum, the bacterium "coasts" for about a half of a microsecond, coming to a stop in a distance less than a tenth the diameter of a hydrogen atom. Similarly, the movement of molecules (nutrients toward, wastes away) in the vicinity of a bacterium is dominated by diffusion. Effective stirring — the generation of bulk flow through mechanical means — is impossible at very low Re. An understanding of the constraints imposed by life at low Reynolds numbers is essentially for understanding the prokaryotic biosphere.

Created with PubMed® Query: "reynolds number" NOT pmcbook NOT ispreviousversion

Citations The Papers (from PubMed®)

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RevDate: 2020-11-27

Arumuru V, Pasa J, SS Samantaray (2020)

Experimental visualization of sneezing and efficacy of face masks and shields.

Physics of fluids (Woodbury, N.Y. : 1994), 32(11):115129.

In the present work, we propose and demonstrate a simple experimental visualization to simulate sneezing by maintaining dynamic similarity to actual sneezing. A pulsed jet with Reynolds number Re = 30 000 is created using compressed air and a solenoid valve. Tracer particles are introduced in the flow to capture the emulated turbulent jet formed due to a sneeze. The visualization is accomplished using a camera and laser illumination. It is observed that a typical sneeze can travel up to 25 ft in ∼22 s in a quiescent environment. This highlights that the present widely accepted safe distance of 6 ft is highly underestimated, especially under the act of a sneeze. Our study demonstrates that a three-layer homemade mask is just adequate to impede the penetration of fine-sized particles, which may cause the spreading of the infectious pathogen responsible for COVID-19. However, a surgical mask cannot block the sneeze, and the sneeze particle can travel up to 2.5 ft. We strongly recommend using at least a three-layer homemade mask with a social distancing of 6 ft to combat the transmission of COVID-19 virus. In offices, we recommend the use of face masks and shields to prevent the spreading of droplets carrying the infectious pathogen. Interestingly, an N-95 mask blocks the sneeze in the forward direction; however, the leakage from the sides and top spreads the sneeze in the backward direction up to 2 ft. We strongly recommend using the elbow or hands to prevent droplet leakage even after wearing a mask during sneezing and coughing.

RevDate: 2020-11-27

Mallik AK, Mukherjee S, MV Panchagnula (2020)

An experimental study of respiratory aerosol transport in phantom lung bronchioles.

Physics of fluids (Woodbury, N.Y. : 1994), 32(11):111903.

The transport and deposition of micrometer-sized particles in the lung is the primary mechanism for the spread of aerosol borne diseases such as corona virus disease-19 (COVID-19). Considering the current situation, modeling the transport and deposition of drops in human lung bronchioles is of utmost importance to determine their consequences on human health. The current study reports experimental observations on deposition in micro-capillaries, representing distal lung bronchioles, over a wide range of Re that imitates the particle dynamics in the entire lung. The experiment investigated deposition in tubes of diameter ranging from 0.3 mm to 2 mm and over a wide range of Reynolds number (10-2 ⩽ Re ⩽ 103). The range of the tube diameter and Re used in this study is motivated by the dimensions of lung airways and typical breathing flow rates. The aerosol fluid was loaded with boron doped carbon quantum dots as fluorophores. An aerosol plume was generated from this mixture fluid using an ultrasonic nebulizer, producing droplets with 6.5 µm as a mean diameter and over a narrow distribution of sizes. The amount of aerosol deposited on the tube walls was measured using a spectrofluorometer. The experimental results show that dimensionless deposition (δ) varies inversely with the bronchiole aspect ratio (L ¯), with the effect of the Reynolds number (Re) being significant only at low L ¯ . δ also increased with increasing dimensionless bronchiole diameter (D ¯), but it is invariant with the particle size based Reynolds number. We show that δ L ¯ ∼ R e - 2 for 10-2 ⩽ Re ⩽ 1, which is typical of a diffusion dominated regime. For Re ⩾ 1, in the impaction dominated regime, δ L ¯ is shown to be independent of Re. We also show a crossover regime where sedimentation becomes important. The experimental results conclude that lower breathing frequency and higher breath hold time could significantly increase the chances of getting infected with COVID-19 in crowded places.

RevDate: 2020-11-21

Battista NA (2020)

Diving into a Simple Anguilliform Swimmer's Sensitivity.

Integrative and comparative biology, 60(5):1236-1250.

Computational models of aquatic locomotion range from modest individual simple swimmers in 2D to sophisticated 3D multi-swimmer models that attempt to parse collective behavioral dynamics. Each of these models contain a multitude of model input parameters to which its outputs are inherently dependent, that is, various performance metrics. In this work, the swimming performance's sensitivity to parameters is investigated for an idealized, simple anguilliform swimming model in 2D. The swimmer considered here propagates forward by dynamically varying its body curvature, similar to motion of a Caenorhabditis elegans. The parameter sensitivities were explored with respect to the fluid scale (Reynolds number), stroke (undulation) frequency, as well as a kinematic parameter controlling the velocity and acceleration of each upstroke and downstroke. The input Reynolds number and stroke frequencies sampled were from [450, 2200] and [1, 3] Hz, respectively. In total, 5000 fluid-structure interaction simulations were performed, each with a unique parameter combination selected via a Sobol sequence, in order to conduct global sensitivity analysis. Results indicate that the swimmer's performance is most sensitive to variations in its stroke frequency. Trends in swimming performance were discovered by projecting the performance data onto particular 2D subspaces. Pareto-like optimal fronts were identified. This work is a natural extension of the parameter explorations of the same model from Battista in 2020.

RevDate: 2020-11-20

Gungor A, A Hemmati (2020)

Wake symmetry impacts the performance of tandem hydrofoils during in-phase and out-of-phase oscillations differently.

Physical review. E, 102(4-1):043104.

The hydrodynamics of two oscillating foils in side-by-side configuration is numerically investigated for in-phase and out-of-phase pitching at Reynolds number of 4000 and Strouhal numbers of St=0.25-0.5. The effects of phase difference (in-phase and out-of-phase) and Strouhal number on symmetric attributes of the wake and unsteady propulsive performance of the foils are studied in detail. At lower Strouhal numbers, there is a quasisteady performance in both thrust generation and power consumption, which coincides with persistence of the wake symmetry. As Strouhal number increases, however, in-phase and out-of-phase pitching display unsteady cycle-averaged behavior with very different wake characteristics. The asymmetric wake of in-phase pitching foils at high Strouhal numbers transitions to a quasisymmetric wake, when an extensive interaction between the two vortex streets is observed in the wake. This coincides with an improvement on the propulsive performance of the foils. In contrast, the symmetric wake of the out-of-phase pitching foils at a high Strouhal number transitions to an asymmetric wake. The adverse effect of this transition is only observed on the propulsive performance of one foil while the other exploits the wake towards a better performance. The collective performance of the the out-of-phase pitching system, however, remains unchanged. There is also a strong correlation between the wake symmetric characteristics and total nonzero side-force production.

RevDate: 2020-11-20

Inubushi M, S Goto (2020)

Transfer learning for nonlinear dynamics and its application to fluid turbulence.

Physical review. E, 102(4-1):043301.

We introduce transfer learning for nonlinear dynamics, which enables efficient predictions of chaotic dynamics by utilizing a small amount of data. For the Lorenz chaos, by optimizing the transfer rate, we accomplish more accurate inference than the conventional method by an order of magnitude. Moreover, a surprisingly small amount of learning is enough to infer the energy dissipation rate of the Navier-Stokes turbulence because we can, thanks to the small-scale universality of turbulence, transfer a large amount of the knowledge learned from turbulence data at lower Reynolds number.

RevDate: 2020-11-19

Ikoma T, Suwa K, Sano M, et al (2020)

Early changes of pulmonary arterial hemodynamics in patients with systemic sclerosis: flow pattern, WSS, and OSI analysis with 4D flow MRI.

European radiology pii:10.1007/s00330-020-07301-x [Epub ahead of print].

OBJECTIVES: To study the pulmonary artery (PA) hemodynamics in patients with systemic sclerosis (SSc) using 4D flow MRI (4D-flow).

METHODS: Twenty-three patients with SSc (M/F: 2/21, 57 ± 15 years, 3 manifest PA hypertension (PAH) by right heart catheterization) and 10 control subjects (M/F: 1/9, 55 ± 17 years) underwent 4D-flow for the in vivo measurement of 3D blood flow velocities in the PA. Data analysis included area-averaged flow quantification at the main PA, 3D wall shear stress (WSS), oscillatory shear index (OSI) calculation along the PA surface, and Reynolds number. The composite outcome of all-cause death and major adverse cardiac events was also investigated.

RESULTS: The maximum PA flow at the systole did not differ, but the minimum flow at the diastole was significantly greater in patients with SSc compared with that in control subjects (7.7 ± 16.0 ml/s vs. ‑ 13.0 ± 17.3 ml/s, p < 0.01). The maximum WSS at the peak systole was significantly lower and OSI was significantly greater in patients with SSc compared with those in control subjects (maximum WSS: 1.04 ± 0.20 Pa vs. 1.33 ± 0.34 Pa, p < 0.01, OSI: 0.139 ± 0.031 vs. 0.101 ± 0.037, p < 0.01). The cumulative event-free rate for the composite event was significantly lower in patients with minimum flow in main PA ≤ 9.22 ml/s (p = 0.012) and in patients with Reynolds number ≤ 2560 (p < 0.001).

CONCLUSIONS: 4D-flow has the potential to detect changes of PA hemodynamics noninvasively and predict the outcome in patients with SSc at the stage before manifest PAH.

KEY POINTS: • The WSS at the peak systolic phase was significantly lower (p < 0.05), whereas OSI was greater (p < 0.01) in patients with SSc without manifest PAH than in controls. • The hemodynamic change detected by 4D-flow may help patient management even at the stage before manifest PAH in SSc. • The minimum PA flow and Reynolds number by 4D-flow will serve as a predictive marker for SSc.

RevDate: 2020-11-17

Lochab V, S Prakash (2020)

Combined electrokinetic and shear flows control colloidal particle distribution across microchannel cross-sections.

Soft matter [Epub ahead of print].

Recent experimental observations on combined electrokinetic and shear flows of colloidal suspensions in rectangular cross-section microfluidic channels have shown unusual cross-stream colloidal particle migration and dynamic assembly. Although a new electrophoresis-induced lift force has been postulated to cause the lateral migration of colloidal particles, little is known about how fluid properties and flow conditions impact this force and therefore subsequent colloidal particle migration. Furthermore, no experimental quantification of this electrophoresis-induced lift force is available. We report several key advances by demonstrating that the kinematic viscosity of the fluid can be used to modulate the spatial distribution of particles over the entire microchannel cross-section, with suppression of the colloidal particle migration observed with increase in fluid kinematic viscosity. Colloidal particle migration of ∼10 μm from not only the top and bottom microchannel walls but also from the side walls is shown with the corresponding electrophoresis-induced lift force of up to ∼30 fN. The breadth of flow conditions tested capture the channel Reynolds number in the 0.1-1.1 range, with inertial migration of colloidal particles shown in flow regimes where the migration was previously thought to be ineffective, if not for the electrophoresis-induced lift force. The ability of the electrophoresis-induced lift force to migrate colloidal particles across the entire microchannel cross-section establishes a new paradigm for three-dimensional control of colloidal particles within confined microchannels.

RevDate: 2020-11-17

Omori T, Ito H, T Ishikawa (2020)

Swimming microorganisms acquire optimal efficiency with multiple cilia.

Proceedings of the National Academy of Sciences of the United States of America pii:2011146117 [Epub ahead of print].

Planktonic microorganisms are ubiquitous in water, and their population dynamics are essential for forecasting the behavior of global aquatic ecosystems. Their population dynamics are strongly affected by these organisms' motility, which is generated by their hair-like organelles, called cilia or flagella. However, because of the complexity of ciliary dynamics, the precise role of ciliary flow in microbial life remains unclear. Here, we have used ciliary hydrodynamics to show that ciliates acquire the optimal propulsion efficiency. We found that ciliary flow highly resists an organism's propulsion and that the swimming velocity rapidly decreases with body size, proportional to the power of minus two. Accordingly, the propulsion efficiency decreases as the cube of body length. By increasing the number of cilia, however, efficiency can be significantly improved, up to 100-fold. We found that there exists an optimal number density of cilia, which provides the maximum propulsion efficiency for all ciliates. The propulsion efficiency in this case decreases inversely proportionally to body length. Our estimated optimal density of cilia corresponds to those of actual microorganisms, including species of ciliates and microalgae, which suggests that now-existing motile ciliates and microalgae have survived by acquiring the optimal propulsion efficiency. These conclusions are helpful for better understanding the ecology of microorganisms, such as the energetic costs and benefits of multicellularity in Volvocaceae, as well as for the optimal design of artificial microswimmers.

RevDate: 2020-11-17

Andersen A, T Kiørboe (2020)

The effect of tethering on the clearance rate of suspension-feeding plankton.

Proceedings of the National Academy of Sciences of the United States of America pii:2017441117 [Epub ahead of print].

Many planktonic suspension feeders are attached to particles or tethered by gravity when feeding. It is commonly accepted that the feeding flows of tethered suspension feeders are stronger than those of their freely swimming counterparts. However, recent flow simulations indicate the opposite, and the cause of the opposing conclusions is not clear. To explore the effect of tethering on suspension feeding, we use a low-Reynolds-number flow model. We find that it is favorable to be freely swimming instead of tethered since the resulting feeding flow past the cell body is stronger, leading to a higher clearance rate. Our result underscores the significance of the near-field flow in shaping planktonic feeding modes, and it suggests that organisms tether for reasons that are not directly fluid dynamical (e.g., to stay near surfaces where the concentration of bacterial prey is high).

RevDate: 2020-11-16

Hatte S, R Pitchumani (2020)

Fractal Model for Drag Reduction on Multiscale Nonwetting Rough Surfaces.

Langmuir : the ACS journal of surfaces and colloids [Epub ahead of print].

Rough surfaces in contact with a flow of fluid exhibit alternating no-slip and free shear boundary conditions at the solid-liquid and air-liquid interfaces, respectively, thereby potentially offering drag reduction benefits. The balance between the dynamic pressure in the flow and the restoring capillary pressure in the interasperity spaces determines the stability of the Cassie state of wettability and is a function of the relative extent of no-slip and free shear regions per unit surface area. In the present study, using a fractal representation of rough surface topography, an analytical model is developed to quantify the stability of the Cassie state of wettability as well as drag reduction and the friction factor for laminar flow in a rectangular channel between nonwetting multiscale rough surfaces. A systematic study is conducted to quantify the effects of fractal parameters of the surfaces and the flow Reynolds number on drag reduction and the friction factor. The studies are used to develop friction factor curves extending the classical Moody diagram to hydrophobic and superhydrophobic surfaces. On the basis of the studies, regime maps are derived for estimating the extent of drag reduction offered by hydrophobic and superhydrophobic surfaces, revealing that superhydrophobic surfaces do not always offer the best drag reduction performance. The application of the fractal model to practical topographies of nonwetting surfaces of copper, aluminum, and zinc oxide fabricated via electrodeposition and etching is also discussed.

RevDate: 2020-11-13

Rader JA, Hedrick TL, He Y, et al (2020)

Functional Morphology of Gliding Flight II. Morphology Follows Predictions of Gliding Performance.

Integrative and comparative biology pii:5903741 [Epub ahead of print].

The evolution of wing morphology among birds, and its functional consequences, remains an open question, despite much attention. This is in part because the connection between form and function is difficult to test directly. To address this deficit, in prior work, we used computational modeling and sensitivity analysis to interrogate the impact of altering wing aspect ratio (AR), camber, and Reynolds number on aerodynamic performance, revealing the performance landscapes that avian evolution has explored. In the present work, we used a dataset of three-dimensionally scanned bird wings coupled with the performance landscapes to test two hypotheses regarding the evolutionary diversification of wing morphology associated with gliding flight behavior: (1) gliding birds would exhibit higher wing AR and greater chordwise camber than their non-gliding counterparts; and (2) that two strategies for gliding flight exist, with divergent morphological conformations. In support of our first hypothesis, we found evidence of morphological divergence in both wing AR and camber between gliders and non-gliders, suggesting that wing morphology of birds that utilize gliding flight is under different selective pressures than the wings of non-gliding taxa. Furthermore, we found that these morphological differences also yielded differences in coefficient of lift measured both at the maximum lift to drag ratio and at minimum sinking speed, with gliding taxa exhibiting higher coefficient of lift in both cases. Minimum sinking speed was also lower in gliders than non-gliders. However, contrary to our hypothesis, we found that the maximum ratio of the coefficient of lift to the coefficient of drag differed between gliders and non-gliders. This may point to the need for gliders to maintain high lift capability for takeoff and landing independent of gliding performance or could be due to the divergence in flight styles among gliders, as not all gliders are predicted to optimize either quantity. However, direct evidence for the existence of two morphologically defined gliding flight strategies was equivocal, with only slightly stronger support for an evolutionary model positing separate morphological optima for these strategies than an alternative model positing a single peak. The absence of a clear result may be an artifact of low statistical power owing to a relatively small sample size of gliding flyers expected to follow the "aerial search" strategy.

RevDate: 2020-11-15

Lee JY, Kottke PA, AG Fedorov (2020)

Hydrodynamics of Vortical Gas Jets Coupled to Point-Like Suction.

Physics of fluids (Woodbury, N.Y. : 1994), 32(10):.

Vortical jet flows in the Reynolds number (Re) range from 1000 to 3425 and swirl number (S) below 0.5, alone and in combination with suction through a small aperture, are experimentally investigated using optical visualization. Schlieren photography is employed to assess the vortical flow structure and establish the fundamental understanding of the source-to-sink gas-dynamic coupling, including the role played by flow rate, jet diameter, and the separation distance between the gas jet source and the suction sink. Compared to vortex-free jets, vortical jets for Re>2700 with swirl number S>0.27 experience earlier laminar-to-turbulent transition, with resulting rapid growth of the jet boundary. The ability to control growth of the jet expansion and mass and momentum dissipation into the surrounding is demonstrated via use of a coaxially aligned flow suction placed in the path of a jet. When a swirling jet is completely coupled with a flow suction, jet expansion is significantly suppressed. The suction/sink flow rate imposes a limit on the maximum input/source flow rate of gas jet to achieve complete coupling. Furthermore, there is a maximum distance over which effective coupling can occur, and for all Reynolds numbers considered this distance is shorter than the distance at which the jet structure breaks up into turbulent eddies in the absence of a sink.

RevDate: 2020-11-11

Astudillo-Castro C, Cordova A, Oyanedel-Craver V, et al (2020)

Prediction of the Limiting Flux and Its Correlation with the Reynolds Number during the Microfiltration of Skim Milk Using an Improved Model.

Foods (Basel, Switzerland), 9(11): pii:foods9111621.

Limiting flux (JL) determination is a critical issue for membrane processing. This work presents a modified exponential model for JL calculation, based on a previously published version. Our research focused on skim milk microfiltrations. The processing variables studied were the crossflow velocity (CFV), membrane hydraulic diameter (dh), temperature, and concentration factor, totaling 62 experimental runs. Results showed that, by adding a new parameter called minimum transmembrane pressure, the modified model not only improved the fit of the experimental data compared to the former version (R2 > 97.00%), but also revealed the existence of a minimum transmembrane pressure required to obtain flux (J). This result is observed as a small shift to the right on J versus transmembrane pressure curves, and this shift increases with the flow velocity. This fact was reported in other investigations, but so far has gone uninvestigated. The JL predicted values were correlated with the Reynolds number (Re) for each dh tested. Results showed that for a same Re; JL increased as dh decreased; in a wide range of Re within the turbulent regime. Finally, from dimensionless correlations; a unique expression JL = f (Re, dh) was obtained; predicting satisfactorily JL (R2 = 84.11%) for the whole set of experiments.

RevDate: 2020-11-10

Ford M, A Santhanakrishnan (2020)

On the role of phase lag in multi-appendage metachronal swimming of euphausiids.

Bioinspiration & biomimetics [Epub ahead of print].

Metachronal paddling is a common method of drag-based aquatic propulsion, in which a series of swimming appendages are oscillated, with the motion of each appendage phase-shifted relative to the neighboring appendages. Ecologically and economically important Euphausiid species such as Antarctic krill (E. superba) swim constantly in the pelagic zone by stroking their paddling appendages (pleopods), with locomotion accounting for the bulk of their metabolic expenditure. They tailor their metachronal swimming gaits for behavioral and energetic needs by changing pleopod kinematics. The functional importance of inter-pleopod phase lag (ϕ) to metachronal swimming performance and wake structure is unknown. To examine this relation, we developed a geometrically and dynamically scaled robot ('krillbot') capable of self-propulsion. Krillbot pleopods were prescribed to mimic published kinematics of fast-forward swimming (FFW) and hovering (HOV) gaits of E. superba, and the Reynolds number and Strouhal number of the krillbot matched well with those calculated for freely-swimming E. superba. In addition to examining published kinematics with uneven ϕ between pleopod pairs, we modified E. superba kinematics to uniformly vary ϕ from 0% to 50% of the cycle. Swimming speed and thrust were largest for FFW with ϕ between 15%-25%, coincident with ϕ range observed in FFW gait of E. superba. In contrast to synchronous rowing (ϕ=0%) where distances between hinged joints of adjacent pleopods were nearly constant throughout the cycle, metachronal rowing (ϕ>0%) brought adjacent pleopods closer together and moved them farther apart. This factor minimized body position fluctuation and augmented metachronal swimming speed. Though swimming speed was lowest for HOV, a ventrally angled downward jet was generated that can assist with weight support during feeding. In summary, our findings show that inter-appendage phase lag can drastically alter both metachronal swimming speed and the large-scale wake structure.

RevDate: 2020-11-07

Ichikawa C, Ishikawa D, Yang JM, et al (2020)

Phenomenological analysis on whipping behavior of rice flour batter.

Journal of food science [Epub ahead of print].

In this study, the bubbles in rice flour batter were investigated under a constant temperature, because the bubble size distribution is important for the control of food texture. We obtained experimental data using a hand mixer and compared the properties of doughs prepared using six rice flours; each flour was prepared through a different milling process. We also added the size effect of the rice flour particles as the Bond number. Furthermore, we performed a dynamic wettability test to estimate the wettability of the rice flour surface. The results of this test were described well by the Washburn equation, and dc cosθ/dp was calculated as a wettability parameter (where, dc = effective diameter of a capillary in a powder bed, cosθ = the contact angle, dp = mean particle diameter of rice flour). If bubble sizes depend mainly on the inertial force, viscous force, surface tension, and gravity, then the normalized mean bubble diameter should be a function of the Reynolds number, Weber number, and Froude number. The mean bubble diameter (dbm) generated by whipping was expected to be affected by the thickness (d) of the rod of the mixer, its movement speed, and physical properties of the material. Therefore, dimensionless mean diameter (dbm /d) was expressed based on a dimensionless equation. In the three-phase dispersion, different empirical equations were obtained depending on the amount of rice flour added, and the bubble diameter could be predicted using dimensionless parameters. In addition, the equations were generally applicable to the various materials selected for this study. PRACTICAL APPLICATION: The powder properties of rice flour were investigated, and dimensionless parameters were analyzed to construct an appropriate process control system for rice flour-based food products. Although the process method optimized for flour products is also used for rice flour products in practical situations, the comprehensive evaluation based on dimensionless parameters leads to optimization of the process for rice-flour based products. Moreover, this optimization might strongly support the creation of a new texture, and thus, the potential for market expansion of rice-flour based products is considerable.

RevDate: 2020-11-10

Sana S, Zivkovic V, K Boodhoo (2020)

Empirical Modelling of Hydrodynamic Effects on Starch Nanoparticles Precipitation in a Spinning Disc Reactor.

Nanomaterials (Basel, Switzerland), 10(11): pii:nano10112202.

Empirical correlations have been developed to relate experimentally determined starch nanoparticle size obtained in a solvent-antisolvent precipitation process with key hydrodynamic parameters of a spinning disc reactor (SDR). Three different combinations of dimensionless groups including a conventional Reynolds number (Re), rotational Reynolds number (Reω) and Rossby number (Ro) have been applied in individual models for two disc surfaces (smooth and grooved) to represent operating variables affecting film flow such as liquid flowrate and disc rotational speed, whilst initial supersaturation (S) has been included to represent varying antisolvent concentrations. Model 1 featuring a combination of Re, Reω and S shows good agreement with the experimental data for both the grooved and smooth discs. For the grooved disc, Re has a greater impact on particle size, whereas Reω is more influential on the smooth disc surface, the difference likely being due to the passive mixing induced by the grooves irrespective of the magnitude of the disc speed. Supersaturation has little impact on particle size within the limited initial supersaturation range studied. Model 2 which characterises both flow rate and disc rotational speed through Ro alone and combined with Re was less accurate in predicting particle size due to several inherent limitations.

RevDate: 2020-11-06

Harvey C, DJ Inman (2020)

Aerodynamic efficiency of gliding birds vs. comparable UAVs: a review.

Bioinspiration & biomimetics [Epub ahead of print].

Here, we reviewed published aerodynamic efficiencies of gliding birds and similar sized unmanned aerial vehicles (UAVs) motivated by a fundamental question: are gliding birds more efficient than comparable UAVs? Despite a multitude of studies that have quantified the aerodynamic efficiency of gliding birds, there is no comprehensive summary of these results. This lack of consolidated information inhibits a true comparison between birds and UAVs. Such a comparison is complicated by variable uncertainty levels between the different techniques used to predict avian efficiency. To support our comparative approach, we began by surveying theoretical and experimental estimates of avian aerodynamic efficiency and investigating the uncertainty associated with each estimation method. We found that the methodology used by a study affects the estimated efficiency and can lead to incongruent conclusions on gliding bird aerodynamic efficiency. Our survey showed that studies on live birds gliding in wind tunnels provide a reliable minimum estimate of a birds' aerodynamic efficiency while simultaneously quantifying the wing configurations used in flight. Next, we surveyed the aeronautical literature to collect the published aerodynamic efficiencies of similar-sized, non-copter UAVs. The compiled information allowed a direct comparison of UAVs and gliding birds. Contrary to our expectation, we found that there is no definitive evidence that any gliding bird species is either more or less efficient than a comparable UAV. This non-result highlights a critical need for new technology and analytical advances that can reduce the uncertainty associated with estimating a gliding bird's aerodynamic efficiency. Nevertheless, our survey indicated that species flying within subcritical Reynolds number regimes may inspire UAV designs that can extend their operational range to efficiently operate in subcritical regimes. The survey results provided here point the way forward for research into avian gliding flight and enable informed UAV designs.

RevDate: 2020-11-10

Friedrich J, Gallon S, Pumir A, et al (2020)

Stochastic Interpolation of Sparsely Sampled Time Series via Multipoint Fractional Brownian Bridges.

Physical review letters, 125(17):170602.

We propose and test a method to interpolate sparsely sampled signals by a stochastic process with a broad range of spatial and/or temporal scales. To this end, we extend the notion of a fractional Brownian bridge, defined as fractional Brownian motion with a given scaling (Hurst) exponent H and with prescribed start and end points, to a bridge process with an arbitrary number of intermediate and nonequidistant points. Determining the optimal value of the Hurst exponent H_{opt}, appropriate to interpolate the sparse signal, is a very important step of our method. We demonstrate the validity of our method on a signal from fluid turbulence in a high Reynolds number flow and discuss the implications of the non-self-similar character of the signal. The method introduced here could be instrumental in several physical problems, including astrophysics, particle tracking, and specific tailoring of surrogate data, as well as in domains of natural and social sciences.

RevDate: 2020-11-06

Coclite A, Coclite GM, D De Tommasi (2020)

Capsules Rheology in Carreau-Yasuda Fluids.

Nanomaterials (Basel, Switzerland), 10(11): pii:nano10112190.

In this paper, a Multi Relaxation Time Lattice Boltzmann scheme is used to describe the evolution of a non-Newtonian fluid. Such method is coupled with an Immersed-Boundary technique for the transport of arbitrarily shaped objects navigating the flow. The no-slip boundary conditions on immersed bodies are imposed through a convenient forcing term accounting for the hydrodynamic force generated by the presence of immersed geometries added to momentum equation. Moreover, such forcing term accounts also for the force induced by the shear-dependent viscosity model characterizing the non-Newtonian behavior of the considered fluid. Firstly, the present model is validated against well-known benchmarks, namely the parabolic velocity profile obtained for the flow within two infinite laminae for five values of the viscosity model exponent, n = 0.25, 0.50, 0.75, 1.0, and 1.5. Then, the flow within a squared lid-driven cavity for Re = 1000 and 5000 (being Re the Reynolds number) is computed as a function of n for a shear-thinning (n < 1) fluid. Indeed, the local decrements in the viscosity field achieved in high-shear zones implies the increment in the local Reynolds number, thus moving the position of near-walls minima towards lateral walls. Moreover, the revolution under shear of neutrally buoyant plain elliptical capsules with different Aspect Ratio (AR = 2 and 3) is analyzed for shear-thinning (n < 1), Newtonian (n = 1), and shear-thickening (n > 1) surrounding fluids. Interestingly, the power law by Huang et al. describing the revolution period of such capsules as a function of the Reynolds number and the existence of a critical value, Rec, after which the tumbling is inhibited in confirmed also for non-Newtonian fluids. Analogously, the equilibrium lateral position yeq of such neutrally buoyant capsules when transported in a plane-Couette flow is studied detailing the variation of yeq as a function of the Reynolds number as well as of the exponent n.

RevDate: 2020-11-11

Kim J, Jin D, Choi H, et al (2020)

A zero-dimensional predictive model for the pressure drop in the stenotic coronary artery based on its geometric characteristics.

Journal of biomechanics, 113:110076 pii:S0021-9290(20)30500-5 [Epub ahead of print].

The diameter- or area-reduction ratio measured from coronary angiography, commonly used in clinical practice, is not accurate enough to represent the functional significance of the stenosis, i.e., the pressure drop across the stenosis. We propose a new zero-dimensional model for the pressure drop across the stenosis considering its geometric characteristics and flow rate. To identify the geometric parameters affecting the pressure drop, we perform three-dimensional numerical simulations for thirty-three patient-specific coronary stenoses. From these numerical simulations, we show that the pressure drop is mostly determined by the curvature as well as the area-reduction ratio of the stenosis before the minimal luminal area (MLA), but heavily depends on the area-expansion ratio after the MLA due to flow separation. Based on this result, we divide the stenosis into the converging and diverging parts in the present zero-dimensional model. The converging part is segmented into a series of straight and curved pipes with curvatures, and the loss of each pipe is estimated by an empirical relation between the total pressure drop, flow rate, and pipe geometric parameters (length, diameter, and curvature). The loss in the diverging part is predicted by a relation among the total pressure drop, Reynolds number, and area expansion ratio with the coefficients determined by a machine learning method. The pressure drops across the stenoses predicted by the present zero-dimensional model agree very well with those obtained from three-dimensional numerical simulations.

RevDate: 2020-11-05

Wang Y, Zhou G, Yan Y, et al (2020)

Construction of Natural Loofah/Poly(vinylidene fluoride) Core-Shell Electrospun Nanofibers via a Controllable Janus Nozzle for Switchable Oil-Water Separation.

ACS applied materials & interfaces [Epub ahead of print].

Developing microstructure and multifunctional membranes toward switchable oil-water separation has been highly desired in oily wastewater treatment. Herein, a controllable Janus nozzle was employed to innovatively electrospin natural loofah/poly(vinylidene fluoride) (PVDF) nanofibers with a core-shell structure for gravity-driven water purification. By adjusting flow rates of the PVDF component, a core-shell structure of the composite fibers was obtained caused by the lower viscosity and surface tension of PVDF. In addition, a steady laminar motion of fluids was constructed based on the Reynolds number of flow fields being less than 2300. In order to investigate the formation mechanism of the microstructure, a series of Janus nozzles with different lengths were controlled to study the blending of the two immiscible components. The gravity difference between the two components might cause disturbance of the jet motion, and the PVDF component unidirectionally encapsulated the loofah to form the shell layer. Most importantly, the dry loofah/PVDF membranes could separate oil from an oil-water mixture, while the water-wetted membrane exhibited switchable separation that could separate water from the mixtures because of the hydroxyl groups of the hydrophilic loofah hydrogen-bonding with water molecules and forming a hydration layer. The composite fibers can be applied in water remediation in practice, and the method to produce core-shell structures seems attractive for technological applications involving macroscopic core-shell nano- or microfibers.

RevDate: 2020-11-11

Jeon W, Ahn J, Kim T, et al (2020)

Intertube Aggregation-Dependent Convective Heat Transfer in Vertically Aligned Carbon Nanotube Channels.

ACS applied materials & interfaces, 12(45):50355-50364.

The heat transfer of carbon nanotube fin geometry has received considerable attention. However, the flow typically occurred over or around the pillars of nanotubes due to the greater flow resistance between the tubes. Here, we investigated the forced convective heat transfer of water through the interstitial space of vertically aligned multiwalled carbon nanotubes (VAMWNTs, intertube distance = 69 nm). The water flow provided significantly a greater Reynolds number (Re) and Nusselt number (Nu) than air flow due to the greater density, heat capacity, and thermal conductivity. However, it resulted in surface tension-induced nanotube aggregation after the flow and drying process, generating random voids in the nanotube channel. This increased permeability (1.27 × 10-11 m2) and Re (2.83 × 10-1) but decreased the heat transfer coefficient (h, 9900 W m-2 K-1) and Nu (53.77), demonstrating a trade-off relationship. The h (25,927 W m-2 K-1) and Nu (153.49) could be further increased, at an equivalent permeability or Re, by increasing nanotube areal density from 2.08 × 1010 to 1.04 × 1011 cm-2. The area-normalized thermal resistance of the densified and aggregated VAMWNTs was smaller than those of the Ni foam, Si microchannel, and carbon nanotube fin array, demonstrating excellent heat transfer characteristics.

RevDate: 2020-11-03

Lyons K, Murphy CT, JA Franck (2020)

Flow over seal whiskers: Importance of geometric features for force and frequency response.

PloS one, 15(10):e0241142.

The complex undulated geometry of seal whiskers has been shown to substantially modify the turbulent structures directly downstream, resulting in a reduction of hydrodynamic forces as well as modified vortex-induced-vibration response when compared with smooth whiskers. Although the unique hydrodynamic response has been well documented, an understanding of the fluid flow effects from each geometric feature remains incomplete. In this computational investigation, nondimensional geometric parameters of the seal whisker morphology are defined in terms of their hydrodynamic relevance, such that wavelength, aspect ratio, undulation amplitudes, symmetry and undulation off-set can be varied independently of one another. A two-factor fractional factorial design of experiments procedure is used to create 16 unique geometries, each of which dramatically amplifies or attenuates the geometric parameters compared with the baseline model. The flow over each unique topography is computed with a large-eddy simulation at a Reynolds number of 500 with respect to the mean whisker thickness and the effects on force and frequency are recorded. The results determine the specific fluid flow impact of each geometric feature which will inform both biologists and engineers who seek to understand the impact of whisker morphology or lay out a framework for biomimetic design of undulated structures.

RevDate: 2020-10-26

Neuhaus L, Hölling M, Bos WJT, et al (2020)

Generation of Atmospheric Turbulence with Unprecedentedly Large Reynolds Number in a Wind Tunnel.

Physical review letters, 125(15):154503.

Generating laboratory flows resembling atmospheric turbulence is of prime importance to study the effect of wind fluctuations on objects such as buildings, vehicles, or wind turbines. A novel driving of an active grid following a stochastic process is used to generate velocity fluctuations with correlation lengths, and, thus, integral scales, much larger than the transverse dimension of the wind tunnel. The combined action of the active grid and a modulation of the fan speed allows one to generate a flow characterized by a four-decade inertial range and an integral scale Reynolds number of 2×10^{7}.

RevDate: 2020-10-30

Domínguez-Pumar M, Kowalski L, Jiménez V, et al (2020)

Analyzing the Performance of a Miniature 3D Wind Sensor for Mars.

Sensors (Basel, Switzerland), 20(20):.

This paper analyzes the behavior of a miniature 3D wind sensor designed for Mars atmosphere. The sensor is a spherical structure of 10 mm diameter divided in four sectors. By setting all the sectors to constant temperature, above that of the air, the 3D wind velocity vector can be measured. Two sets of experiments have been performed. First, an experimental campaign made under typical Mars conditions at the Aarhus Wind Tunnel Simulator is presented. The results demonstrate that both wind speed and angle can be efficiently measured, using a simple inverse algorithm. The effect of sudden wind changes is also analyzed and fast response times in the range of 0.7 s are obtained. The second set of experiments is focused on analyzing the performance of the sensor under extreme Martian wind conditions, reaching and going beyond the Dust Devil scale. To this purpose, both high-fidelity numerical simulations of fluid dynamics and heat transfer and experiments with the sensor have been performed. The results of the experiments, made for winds in the Reynolds number 1000-2000 range, which represent 65-130 m/s of wind speed under typical Mars conditions, further confirm the simulation predictions and show that it will be possible to successfully measure wind speed and direction even under these extreme regimes.

RevDate: 2020-10-20

Czelusniak LE, Mapelli VP, Guzella MS, et al (2020)

Force approach for the pseudopotential lattice Boltzmann method.

Physical review. E, 102(3-1):033307.

One attractive feature of the original pseudopotential method consists on its simplicity of adding a force dependent on a nearest-neighbor potential function. In order to improve the method, regarding thermodynamic consistency and control of surface tension, different approaches were developed in the literature, such as multirange interactions potential and modified forcing schemes. In this work, a strategy to combine these enhancements with an appropriate interaction force field using only nearest-neighbor interactions is devised, starting from the desired pressure tensor. The final step of our procedure is implementing this external force by using the classical Guo forcing scheme. Numerical tests regarding static and dynamic flow conditions were performed. Static tests showed that current procedure is suitable to control the surface tension and phase densities. Based on thermodynamic principles, it is devised a solution for phase densities in a droplet, which states explicitly dependence on the surface tension and interface curvature. A comparison with numerical results suggest a physical inconsistency in the pseudopotential method. This fact is not commonly discussed in the literature, since most of studies are limited to the Maxwell equal area rule. However, this inconsistency is shown to be dependent on the equation of state (EOS), and its effects can be mitigated by an appropriate choice of Carnahan-Starling EOS parameters. Also, a droplet oscillation test was performed, and the most divergent solution under certain flow conditions deviated 7.5% from the expected analytical result. At the end, a droplet impact test against a solid wall was performed to verify the method stability, and it was possible to reach stable simulation results with density ratio of almost 2400 and Reynolds number of Re=373. The observed results corroborate that the proposed method is able to replicate the desired macroscopic multiphase behavior.

RevDate: 2020-10-20

Rana N, P Perlekar (2020)

Coarsening in the two-dimensional incompressible Toner-Tu equation: Signatures of turbulence.

Physical review. E, 102(3-1):032617.

We investigate coarsening dynamics in the two-dimensional, incompressible Toner-Tu equation. We show that coarsening proceeds via vortex merger events, and the dynamics crucially depend on the Reynolds number Re. For low Re, the coarsening process has similarities to Ginzburg-Landau dynamics. On the other hand, for high Re, coarsening shows signatures of turbulence. In particular, we show the presence of an enstrophy cascade from the intervortex separation scale to the dissipation scale.

RevDate: 2020-10-20

Bos WJT, Laadhari F, W Agoua (2020)

Linearly forced isotropic turbulence at low Reynolds numbers.

Physical review. E, 102(3-1):033105.

We investigate the forcing strength needed to sustain a flow using linear forcing. A critical Reynolds number R_{c} is determined, based on the longest wavelength allowed by the system, the forcing strength and the viscosity. A simple model is proposed for the dissipation rate, leading to a closed expression for the kinetic energy of the flow as a function of the Reynolds number. The dissipation model and the prediction for the kinetic energy are assessed using direct numerical simulations and two-point closure integrations. An analysis of the dissipation-rate equation and the triadic structure of the nonlinear transfer allows to refine the model in order to reproduce the low-Reynolds-number asymptotic behavior, where the kinetic energy is proportional to R-R_{c}.

RevDate: 2020-10-20

Rinoshika H, Rinoshika A, JJ Wang (2020)

Three-dimensional multiscale flow structures behind a wall-mounted short cylinder based on tomographic particle image velocimetry and three-dimensional orthogonal wavelet transform.

Physical review. E, 102(3-1):033101.

Three-dimensional (3D) flow structures around a wall-mounted short cylinder of height-to-diameter ratio 1 were instantaneously measured by a high-resolution tomographic particle image velocimetry (Tomo-PIV) at Reynolds number of 10 720 in a water tunnel. 3D velocity fields, 3D vorticity, the Q criterion, the rear separation region, and the characteristic of arch type vortex and tip vortices were first discussed. We found a strong 3D W-type arch vortex behind the short cylinder, which was originated by the interaction between upwash and downwash flows. This W-type arch vortex was reshaped to the M-shaped arch vortex downstream. It indicated that the head shape of the arch vortex structure depended on the aspect ratio of the cylinder. The large-scale streamwise vortices were originated by the downwash and upwash flows near the center location of W-type arch vortex. Then the 3D orthogonal wavelet multiresolution technique was developed to analyze instantaneous 3D velocity fields of Tomo-PIV in order to clarify 3D multiscale wake flow structures. The W-type shape arch vortex was extracted in the time-averaged intermediate-scale structure, while an M-shaped arch vortex was identified in the time-averaged large-scale structure. The tip vortices distributed in the time-averaged large- and intermediate-scale structures. The instantaneous intermediate-scale upwash vortices played an essential role in producing W-type head of arch structure. It was also observed that strong small-scale vortices appeared in the shear layer or near the bottom plate and most of them were contained in the intermediate-scale structures.

RevDate: 2020-10-22

Riasat S, Ramzan M, Kadry S, et al (2020)

Significance of magnetic Reynolds number in a three-dimensional squeezing Darcy-Forchheimer hydromagnetic nanofluid thin-film flow between two rotating disks.

Scientific reports, 10(1):17208.

The remarkable aspects of carbon nanotubes like featherweight, durability, exceptional electrical and thermal conduction capabilities, and physicochemical stability make them desirous materials for electrochemical devices. Having such astonishing characteristics of nanotubes in mind our aspiration is to examine the squeezing three dimensional Darcy-Forchheimer hydromagnetic nanofluid thin-film flow amid two rotating disks with suspended multiwalled carbon nanotubes (MWCNTs) submerged into the base fluid water. The analysis is done by invoking partial slip effect at the boundary in attendance of autocatalytic reactions. The mathematical model consists of axial and azimuthal momentum and magnetic fields respectively. The tangential and axial velocity profiles and components of the magnetic field are examined numerically by employing the bvp4c method for varying magnetic, rotational, and squeezing Reynolds number. The torque effect near the upper and lower disks are studied critically using their graphical depiction. The values of the torque at the upper and lower disks are obtained for rotational and squeezed Reynolds numbers and are found in an excellent concurrence when compared with the existing literature. Numerically it is computed that the torque at the lower disk is higher in comparison to the upper disk for mounting estimates of the squeezed Reynolds number and the dimensionless parameter for magnetic force in an axial direction. From the graphical illustrations, it is learned that thermal profile declines for increasing values of the squeezed Reynolds number.

RevDate: 2020-10-13

Wong JY, Chan BKK, KYK Chan (2020)

Swimming kinematics and hydrodynamics of barnacle larvae throughout development.

Proceedings. Biological sciences, 287(1936):20201360.

Changes in size strongly influence organisms' ecological performances. For aquatic organisms, they can transition from viscosity- to inertia-dominated fluid regimes as they grow. Such transitions are often associated with changes in morphology, swimming speed and kinematics. Barnacles do not fit into this norm as they have two morphologically distinct planktonic larval phases that swim differently but are of comparable sizes and operate in the same fluid regime (Reynolds number 100-101). We quantified the hydrodynamics of the rocky intertidal stalked barnacle Capitulum mitella from the nauplius II to cyprid stage and examined how kinematics and size increases affect its swimming performance. Cyprids beat their appendages in a metachronal wave to swim faster, more smoothly, and with less backwards slip per beat cycle than did all naupliar stages. Micro-particle image velocimetry showed that cyprids generated trailing viscous vortex rings that pushed water backwards for propulsion, contrary to the nauplii's forward suction current for particle capture. Our observations highlight that zooplankton swimming performance can shift via morphological and kinematic modifications without a significant size increase. The divergence in ecological functions through ontogeny in barnacles and the removal of feeding requirement likely contributed to the evolution of the specialized, taxonomically unique cyprid phase.

RevDate: 2020-10-13

Jakob J, Gross M, T Gunther (2020)

A Fluid Flow Data Set for Machine Learning and its Application to Neural Flow Map Interpolation.

IEEE transactions on visualization and computer graphics, PP: [Epub ahead of print].

In recent years, deep learning has opened countless research opportunities across many different disciplines. At present, visualization is mainly applied to explore and explain neural networks. Its counterpart-the application of deep learning to visualization problems-requires us to share data more openly in order to enable more scientists to engage in data-driven research. In this paper, we construct a large fluid flow data set and apply it to a deep learning problem in scientific visualization. Parameterized by the Reynolds number, the data set contains a wide spectrum of laminar and turbulent fluid flow regimes. The full data set was simulated on a high-performance compute cluster and contains 8000 time-dependent 2D vector fields, accumulating to more than 16 TB in size. Using our public fluid data set, we trained deep convolutional neural networks in order to set a benchmark for an improved post-hoc Lagrangian fluid flow analysis. In in-situ settings, flow maps are exported and interpolated in order to assess the transport characteristics of time-dependent fluids. Using deep learning, we improve the accuracy of flow map interpolations, allowing a more precise flow analysis at a reduced memory IO footprint.

RevDate: 2020-10-06

Di Luca M, Mintchev S, Su Y, et al (2020)

A bioinspired Separated Flow wing provides turbulence resilience and aerodynamic efficiency for miniature drones.

Science robotics, 5(38):.

Small-scale drones have enough sensing and computing power to find use across a growing number of applications. However, flying in the low-Reynolds number regime remains challenging. High sensitivity to atmospheric turbulence compromises vehicle stability and control, and low aerodynamic efficiency limits flight duration. Conventional wing designs have thus far failed to address these two deficiencies simultaneously. Here, we draw inspiration from nature's small flyers to design a wing with lift generation robust to gusts and freestream turbulence without sacrificing aerodynamic efficiency. This performance is achieved by forcing flow separation at the airfoil leading edge. Water and wind tunnel measurements are used to demonstrate the working principle and aerodynamic performance of the wing, showing a substantial reduction in the sensitivity of lift force production to freestream turbulence, as compared with the performance of an Eppler E423 low-Reynolds number wing. The minimum cruise power of a custom-built 104-gram fixed-wing drone equipped with the Separated Flow wing was measured in the wind tunnel indicating an upper limit for the flight time of 170 minutes, which is about four times higher than comparable existing fixed-wing drones. In addition, we present scaling guidelines and outline future design and manufacturing challenges.

RevDate: 2020-10-20

Phelps PR, Lee CA, DM Morton (2020)

Episodes of fast crystal growth in pegmatites.

Nature communications, 11(1):4986.

Pegmatites are shallow, coarse-grained magmatic intrusions with crystals occasionally approaching meters in length. Compared to their plutonic hosts, pegmatites are thought to have cooled rapidly, suggesting that these large crystals must have grown fast. Growth rates and conditions, however, remain poorly constrained. Here we investigate quartz crystals and their trace element compositions from miarolitic cavities in the Stewart pegmatite in southern California, USA, to quantify crystal growth rates. Trace element concentrations deviate considerably from equilibrium and are best explained by kinetic effects associated with rapid crystal growth. Kinetic crystal growth theory is used to show that crystals accelerated from an initial growth rate of 10-6-10-7 m s-1 to 10-5-10-4 m s-1 (10-100 mm day-1 to 1-10 m day-1), indicating meter sized crystals could have formed within days, if these rates are sustained throughout pegmatite formation. The rapid growth rates require that quartz crystals grew from thin (micron scale) chemical boundary layers at the fluid-crystal interfaces. A strong advective component is required to sustain such thin boundary layers. Turbulent conditions (high Reynolds number) in these miarolitic cavities are shown to exist during crystallization, suggesting that volatile exsolution, crystallization, and cavity generation occur together.

RevDate: 2020-10-30

Qiu Y, Hu W, Wu C, et al (2020)

An Experimental Study of Microchannel and Micro-Pin-Fin Based On-Chip Cooling Systems with Silicon-to-Silicon Direct Bonding.

Sensors (Basel, Switzerland), 20(19):.

This paper describes an experimental study of the cooling capabilities of microchannel and micro-pin-fin based on-chip cooling systems. The on-chip cooling systems integrated with a micro heat sink, simulated power IC (integrated circuit) and temperature sensors are fabricated by micromachining and silicon-to-silicon direct bonding. Three micro heat sink structures: a microchannel heat sink (MCHS), an inline micro-pin-fin heat sink (I-MPFHS) and a staggered micro-pin-fin heat sink (S-MPFHS) are tested in the Reynolds number range of 79.2 to 882.3. The results show that S-MPFHS is preferred if the water pump can provide enough pressure drop. However, S-MPFHS has the worst performance when the rated pressure drop of the pump is lower than 1.5 kPa because the endwall effect under a low Reynolds number suppresses the disturbance generated by the staggered micro pin fins but S-MPFHS is still preferred when the rated pressure drop of the pump is in the range of 1.5 to 20 kPa. When the rated pressure drop of the pump is higher than 20 kPa, I-MPFHS will be the best choice because of high heat transfer enhancement and low pressure drop price brought by the unsteady vortex street.

RevDate: 2020-10-08

Chen Y, Chen Y, Hu S, et al (2020)

Continuous ultrasonic flow measurement for aerospace small pipelines.

Ultrasonics, 109:106260 pii:S0041-624X(20)30199-2 [Epub ahead of print].

Aerospace explorations stimulate extensive research on innovative propellant flow measurement technologies in microgravity conditions. Ultrasonic-based measurements have advantages of non-invasive and non-moving-component constructions as well as fast responses to bi-directional flow detection, its applications in aerospace explorations have already been reported. To avoid the shortages of pulse ultrasonic measurement configurations, flow measurement of continuous ultrasonic wave propagation is presented to match the requirements of large measurement range and high precision. Fabrication process and laboratory validations using water flow are presented. Ground experiments show that the linearity of the proposed ultrasonic flow meter is obtained in the measurement range [0, 80 ml/s] which is typical requirement in aerospace applications. Meanwhile, the fitted linear feature from the experimental data matches well the theoretical prediction except the flow prediction of stationary fluid. Under specific configurations, the absolute measurement error is significantly affected by the corresponding Reynolds number. Furthermore, the absolute measurement error is smaller when excitation signals with higher frequency are used if the phase tracking performance for different frequencies is identical.

RevDate: 2020-10-01

Ye Y, Luo X, Dong C, et al (2020)

Numerical and Experimental Investigation of Soot Suppression by Acoustic Oscillated Combustion.

ACS omega, 5(37):23866-23875.

The soot suppression by acoustic oscillations for acetylene diffusion flames was investigated combining numerical and experimental studies. The combustion and soot formation were predicted by the finite-rate detailed chemistry model and modified Moss-Brookes model, respectively, while the turbulence was predicted by the detached eddy simulation (DES) with a low Reynolds number correction. Experimental results showed that the soot rate almost decreased linearly with the amplitude of acoustic oscillation, and the pinch-off of the flame occurred at a large acoustic oscillation. Numerical results showed that the flame structure was well predicted, while the soot rate was over-predicted at large acoustic oscillations; the consumption of O2 increased obviously with the acoustic oscillation. The soot suppression was mainly caused by the decrease of the surface growth rate when the air was pushed toward the flame.

RevDate: 2020-10-01

Dbouk T, D Drikakis (2020)

Weather impact on airborne coronavirus survival.

Physics of fluids (Woodbury, N.Y. : 1994), 32(9):093312.

The contribution of this paper toward understanding of airborne coronavirus survival is twofold: We develop new theoretical correlations for the unsteady evaporation of coronavirus (CoV) contaminated saliva droplets. Furthermore, we implement the new correlations in a three-dimensional multiphase Eulerian-Lagrangian computational fluid dynamics solver to study the effects of weather conditions on airborne virus transmission. The new theory introduces a thermal history kernel and provides transient Nusselt (Nu) and Sherwood (Sh) numbers as a function of the Reynolds (Re), Prandtl (Pr), and Schmidt numbers (Sc). For the first time, these new correlations take into account the mixture properties due to the concentration of CoV particles in a saliva droplet. We show that the steady-state relationships induce significant errors and must not be applied in unsteady saliva droplet evaporation. The classical theory introduces substantial deviations in Nu and Sh values when increasing the Reynolds number defined at the droplet scale. The effects of relative humidity, temperature, and wind speed on the transport and viability of CoV in a cloud of airborne saliva droplets are also examined. The results reveal that a significant reduction of virus viability occurs when both high temperature and low relative humidity occur. The droplet cloud's traveled distance and concentration remain significant at any temperature if the relative humidity is high, which is in contradiction with what was previously believed by many epidemiologists. The above could explain the increase in CoV cases in many crowded cities around the middle of July (e.g., Delhi), where both high temperature and high relative humidity values were recorded one month earlier (during June). Moreover, it creates a crucial alert for the possibility of a second wave of the pandemic in the coming autumn and winter seasons when low temperatures and high wind speeds will increase airborne virus survival and transmission.

RevDate: 2020-11-06

York CA, Bartol IK, Krueger PS, et al (2020)

Squids use multiple escape jet patterns throughout ontogeny.

Biology open, 9(11): pii:bio.054585.

Throughout their lives, squids are both predators and prey for a multitude of animals, many of which are at the top of ocean food webs, making them an integral component of the trophic structure of marine ecosystems. The escape jet, which is produced by the rapid expulsion of water from the mantle cavity through a funnel, is central to a cephalopod's ability to avoid predation throughout its life. Although squid undergo morphological and behavioral changes and experience remarkably different Reynolds number regimes throughout their development, little is known about the dynamics and propulsive efficiency of escape jets throughout ontogeny. We examine the hydrodynamics and kinematics of escape jets in squid throughout ontogeny using 2D/3D velocimetry and high-speed videography. All life stages of squid produced two escape jet patterns: (1) 'escape jet I' characterized by short rapid pulses resulting in vortex ring formation and (2) 'escape jet II' characterized by long high-volume jets, often with a leading-edge vortex ring. Paralarvae exhibited higher propulsive efficiency than adult squid during escape jet ejection, and propulsive efficiency was higher for escape jet I than escape jet II in juveniles and adults. These results indicate that although squid undergo major ecological transitions and morphology changes from paralarvae to adults, all life stages demonstrate flexibility in escape jet responses and produce escape jets of surprisingly high propulsive efficiency.This article has an associated First Person interview with the first author of the paper.

RevDate: 2020-10-29

Saqr KM, Tupin S, Rashad S, et al (2020)

Physiologic blood flow is turbulent.

Scientific reports, 10(1):15492.

Contemporary paradigm of peripheral and intracranial vascular hemodynamics considers physiologic blood flow to be laminar. Transition to turbulence is considered as a driving factor for numerous diseases such as atherosclerosis, stenosis and aneurysm. Recently, turbulent flow patterns were detected in intracranial aneurysm at Reynolds number below 400 both in vitro and in silico. Blood flow is multiharmonic with considerable frequency spectra and its transition to turbulence cannot be characterized by the current transition theory of monoharmonic pulsatile flow. Thus, we decided to explore the origins of such long-standing assumption of physiologic blood flow laminarity. Here, we hypothesize that the inherited dynamics of blood flow in main arteries dictate the existence of turbulence in physiologic conditions. To illustrate our hypothesis, we have used methods and tools from chaos theory, hydrodynamic stability theory and fluid dynamics to explore the existence of turbulence in physiologic blood flow. Our investigation shows that blood flow, both as described by the Navier-Stokes equation and in vivo, exhibits three major characteristics of turbulence. Womersley's exact solution of the Navier-Stokes equation has been used with the flow waveforms from HaeMod database, to offer reproducible evidence for our findings, as well as evidence from Doppler ultrasound measurements from healthy volunteers who are some of the authors. We evidently show that physiologic blood flow is: (1) sensitive to initial conditions, (2) in global hydrodynamic instability and (3) undergoes kinetic energy cascade of non-Kolmogorov type. We propose a novel modification of the theory of vascular hemodynamics that calls for rethinking the hemodynamic-biologic links that govern physiologic and pathologic processes.

RevDate: 2020-09-22

Gibson BM, Furbish DJ, Rahman IA, et al (2020)

Ancient life and moving fluids.

Biological reviews of the Cambridge Philosophical Society [Epub ahead of print].

Over 3.7 billion years of Earth history, life has evolved complex adaptations to help navigate and interact with the fluid environment. Consequently, fluid dynamics has become a powerful tool for studying ancient fossils, providing insights into the palaeobiology and palaeoecology of extinct organisms from across the tree of life. In recent years, this approach has been extended to the Ediacara biota, an enigmatic assemblage of Neoproterozoic soft-bodied organisms that represent the first major radiation of macroscopic eukaryotes. Reconstructing the ways in which Ediacaran organisms interacted with the fluids provides new insights into how these organisms fed, moved, and interacted within communities. Here, we provide an in-depth review of fluid physics aimed at palaeobiologists, in which we dispel misconceptions related to the Reynolds number and associated flow conditions, and specify the governing equations of fluid dynamics. We then review recent advances in Ediacaran palaeobiology resulting from the application of computational fluid dynamics (CFD). We provide a worked example and account of best practice in CFD analyses of fossils, including the first large eddy simulation (LES) experiment performed on extinct organisms. Lastly, we identify key questions, barriers, and emerging techniques in fluid dynamics, which will not only allow us to understand the earliest animal ecosystems better, but will also help to develop new palaeobiological tools for studying ancient life.

RevDate: 2020-09-22

Sonnenberg AH, Taylor E, Mondoñedo JR, et al (2020)

Breath Hold Facilitates Targeted Deposition of Aerosolized Droplets in a 3D Printed Bifurcating Airway Tree.

Annals of biomedical engineering pii:10.1007/s10439-020-02623-9 [Epub ahead of print].

The lungs have long been considered a desired route for drug delivery but, there is still a lack of strategies to rationally target delivery sites especially in the presence of heterogeneous airway disease. Furthermore, no standardized system has been proposed to rapidly test different ventilation strategies and how they alter the overall and regional deposition pattern in the airways. In this study, a 3D printed symmetric bifurcating tree model mimicking part of the human airway tree was developed that can be used to quantify the regional deposition patterns of different delivery methodologies. The model is constructed in a novel way that allows for repeated measurements of regional deposition using reusable parts. During ventilation, nebulized ~3-micron-sized fluid droplets were delivered into the model. Regional delivery, quantified by precision weighing individual airways, was highly reproducible. A successful strategy to control regional deposition was achieved by combining an inspiratory wave form with a "breath hold" pause after each inspiration. Specifically, the second generation of the tree was successfully targeted, and deposition was increased by up to four times in generation 2 when compared to a ventilation without the breath hold (p < 0.0001). Breath hold was also demonstrated to facilitate deposition into blocked regions of the model, which mimic airway closure during an asthma that receive no flow during inhalation. Additionally, visualization experiments demonstrated that in the absence of fluid flow, the deposition of 3-micron water droplets is dominated by gravity, which, to our knowledge, has not been confirmed under standard laboratory conditions.

RevDate: 2020-09-28

Bortot M, Sharifi A, Ashworth K, et al (2020)

Pathologic Shear and Elongation Rates Do Not Cause Cleavage of Von Willebrand Factor by ADAMTS13 in a Purified System.

Cellular and molecular bioengineering, 13(4):379-390.

Introduction: Pathological flows in patients with severe aortic stenosis are associated with acquired von Willebrand syndrome. This syndrome is characterized by excessive cleavage of von Willebrand factor by its main protease, A Disintegrin and Metalloproteinase with a Thrombospondin Type 1 Motif, Member 13 (ADAMTS13) leading to decreased VWF function and mucocutaneous bleeding. Aortic valve replacement and correction of the flow behavior to physiological levels reverses the syndrome, supporting the association between pathological flow and acquired von Willebrand syndrome. We investigated the effects of shear and elongational rates on von Willebrand factor cleavage in the presence of ADAMTS13.

Methods: We identified acquired von Willebrand syndrome in five patients with severe aortic stenosis. Doppler echography values from these patients were used to develop three computational fluid dynamic (CFD) aortic valve models (normal, mild and severe stenosis). Shear, elongational rates and exposure times identified in the CFD simulations were used as parameters for the design of microfluidic devices to test the effects of pathologic shear and elongational rates on the structure and function of von Willebrand factor.

Results: The shear rates (0-10,000s-1), elongational rates (0-1000 s-1) and exposure times (1-180 ms) tested in our microfluidic designs mimicked the flow features identified in patients with aortic stenosis. The shear and elongational rates tested in vitro did not lead to excessive cleavage or decreased function of von Willebrand factor in the presence of the protease.

Conclusions: High shear and elongational rates in the presence of ADAMTS13 are not sufficient for excessive cleavage of von Willebrand Factor.

RevDate: 2020-10-05

Gao D, Bai M, Hu C, et al (2020)

Investigating control of convective heat transfer and flow resistance of Fe3O4/deionized water nanofluid in magnetic field in laminar flow.

Nanotechnology, 31(49):495402.

This paper studies the convective heat transfer and flow resistance of Fe3O4/deionized water nanofluids in laminar flow under the control of an external magnetic field. The basic thermophysical parameters including viscosity, specific heat capacity and thermal conductivity are investigated to describe the fundamental performance of heat transfer and flow resistance. In the absence of the magnetic field, the heat transfer coefficients and flow friction could not change significantly at nanoparticle volume concentration of 0.05%. In the presence of the magnetic field, it can enhance heat transfer and flow resistance by 6% and 3.5% when the magnets interlace on both sides of the tube. The dynamic magnetic experiments discussed the heat transfer increase process in detail. The heat transfer and the flow resistance increase by 11.7% and 5.4% when magnetic field strength is 600 Gs, nanoparticle volume concentration is 2% and Reynolds number is 2000. The radial shuttle movement of magnetic nanoparticles in the cross-section, micro convection in base fluid and the slip velocity between the nanoparticles and the base fluid are considered the main reasons for heat transfer enhancement.

RevDate: 2020-09-18

Mukhopadhyay S, A Mukhopadhyay (2020)

Waves and instabilities of viscoelastic fluid film flowing down an inclined wavy bottom.

Physical review. E, 102(2-1):023117.

Evolution of waves and hydrodynamic instabilities of a thin viscoelastic fluid film flowing down an inclined wavy bottom of moderate steepness have been analyzed analytically and numerically. The classical long-wave expansion method has been used to formulate a nonlinear evolution equation for the development of the free surface. A normal-mode approach has been adopted to discuss the linear stability analysis from the viewpoint of the spatial and temporal study. The method of multiple scales is used to derive a Ginzburg-Landau-type nonlinear equation for studying the weakly nonlinear stability solutions. Two significant wave families, viz., γ_{1} and γ_{2}, are found and discussed in detail along with the traveling wave solution of the evolution system. A time-dependent numerical study is performed with Scikit-FDif. The entire investigation is conducted primarily for a general periodic bottom, and the detailed results of a particular case study of sinusoidal topography are then discussed. The case study reveals that the bottom steepness ζ plays a dual role in the linear regime. Increasing ζ has a stabilizing effect in the uphill region, and the opposite occurs in the downhill region. While the viscoelastic parameter Γ has a destabilizing effect throughout the domain in both the linear and the nonlinear regime. Both supercritical and subcritical solutions are possible through a weakly nonlinear analysis. It is interesting to note that the unconditional zone decreases and the explosive zone increases in the downhill region rather than the uphill region for a fixed Γ and ζ. The same phenomena occur in a particular region if we increase Γ and keep ζ fixed. The traveling wave solution reveals the fact that to get the γ_{1} family of waves we need to increase the Reynolds number a bit more than the value at which the γ_{2} family of waves is found. The spatiotemporal evolution of the nonlinear surface equation indicates that different kinds of finite-amplitude permanent waves exist.

RevDate: 2020-09-18

Hassan MR, C Wang (2020)

Lateral migration of a ferrofluid droplet in a plane Poiseuille flow under uniform magnetic fields.

Physical review. E, 102(2-1):022611.

The lateral migration of a two-dimensional (2D) viscous ferrofluid droplet in a plane Poiseuille flow under a uniform magnetic field is studied numerically by using the level set method. Focusing on low droplet Reynolds number flows (Re_{d}≤0.05), several numerical simulations are carried out to analyze the effects of magnetic field direction and strength, droplet size, and viscosity ratio on the lateral migration behavior of the droplet. The results indicate that the magnetic field direction plays a pivotal role in the trajectory of lateral migration of the droplet and the final equilibrium position in the channel. When the magnetic field is parallel to the channel, i.e., α=0^{∘} (the direction of magnetic field), the droplet is found to settle closer to the wall with an increase in magnetic Bond number Bo_{m}, while at α=45^{∘}, the droplet settles closer to the channel center. Varying the initial droplet sizes at a fixed magnetic Bond number Bo_{m} and viscosity ratio λ results in different final equilibrium positions within the channel. Additionally, the effect of different viscosity ratios on the migration behavior of the droplet is examined at variable magnetic Bond numbers Bo_{m}. At α=45^{∘}, a critical steady state of deformation is found for λ=0.5 and 1 where the droplet changes its migration direction and shifts toward the center of the channel, while at λ=0.05, the droplet crosses the center. At α=90^{∘}, the droplet is found to settle exactly at the center of the flow domain irrespective of different magnetic Bond numbers, droplet sizes, and viscosity ratios.

RevDate: 2020-09-30

Beratlis N, Capuano F, Krishnan K, et al (2020)

Direct numerical simulations of a great horn owl in flapping flight.

Integrative and comparative biology pii:5905490 [Epub ahead of print].

The fluid dynamics of owls in flapping flight is studied by coordinated experiments and computations. The great horned owl was selected, which is nocturnal, stealthy, and relatively large sized raptor. On the experimental side, perch-to-perch flight was considered in an open wind tunnel. The owl kinematics were captured with multiple cameras from different view angles. The kinematic extraction was central in driving the computations, which were designed to resolve all significant spatio-temporal scales in the flow with an unprecedented level of resolution. The wing geometry was extracted from the planform image of the owl wing and a three-dimensional model, the reference configuration, was reconstructed. This configuration was then deformed in time to best match the kinematics recorded during flights utilizing an image-registration technique based on the large deformation diffeomorphic metric mapping framework. All simulations were conducted using an eddy-resolving, high-fidelity, solver, where the large displacements/deformations of the flapping owl model were introduced with an immersed boundary formulation. We report detailed information on the spatio-temporal flow dynamics in the near wake including variables that are challenging to measure with sufficient accuracy, such as aerodynamic forces. At the same time our results indicate that high-fidelity computations over smooth wings may have limitations in capturing the full range of flow phenomena in owl flight. The growth and subsequent separation of the laminar boundary layers developing over the wings in this Reynolds number regime is sensitive to the surface micro-features that are unique to each specie.

RevDate: 2020-09-15

Sprenger AR, Shaik VA, Ardekani AM, et al (2020)

Towards an analytical description of active microswimmers in clean and in surfactant-covered drops.

The European physical journal. E, Soft matter, 43(9):58 pii:10.1140/epje/i2020-11980-9.

Geometric confinements are frequently encountered in the biological world and strongly affect the stability, topology, and transport properties of active suspensions in viscous flow. Based on a far-field analytical model, the low-Reynolds-number locomotion of a self-propelled microswimmer moving inside a clean viscous drop or a drop covered with a homogeneously distributed surfactant, is theoretically examined. The interfacial viscous stresses induced by the surfactant are described by the well-established Boussinesq-Scriven constitutive rheological model. Moreover, the active agent is represented by a force dipole and the resulting fluid-mediated hydrodynamic couplings between the swimmer and the confining drop are investigated. We find that the presence of the surfactant significantly alters the dynamics of the encapsulated swimmer by enhancing its reorientation. Exact solutions for the velocity images for the Stokeslet and dipolar flow singularities inside the drop are introduced and expressed in terms of infinite series of harmonic components. Our results offer useful insights into guiding principles for the control of confined active matter systems and support the objective of utilizing synthetic microswimmers to drive drops for targeted drug delivery applications.

RevDate: 2020-10-30

Khan MZU, Uddin E, Akbar B, et al (2020)

Investigation of Heat Transfer and Pressure Drop in Microchannel Heat Sink Using Al2O3 and ZrO2 Nanofluids.

Nanomaterials (Basel, Switzerland), 10(9):.

A new micro heat exchanger was analyzed using numerical formulation of conjugate heat transfer for single-phase fluid flow across copper microchannels. The flow across bent channels harnesses asymmetric laminar flow and dean vortices phenomena for heat transfer enhancement. The single-channel analysis was performed to select the bent channel aspect ratio by varying width and height between 35-300 μm for Reynolds number and base temperature magnitude range of 100-1000 and 320-370 K, respectively. The bent channel results demonstrate dean vortices phenomenon at the bend for Reynolds number of 500 and above. Thermal performance factor analysis shows an increase of 18% in comparison to straight channels of 200 μm width and height. Alumina nanoparticles at 1% and 3% concentration enhance the Nusselt number by an average of 10.4% and 23.7%, respectively, whereas zirconia enhances Nusselt number by 16% and 33.9% for same concentrations. On the other hand, thermal performance factor analysis shows a significant increase in pressure drop at high Reynolds number with 3% particle concentration. Using zirconia for nanofluid, Nusselt number of the bent multi-channel model is improved by an average of 18% for a 3% particle concentration as compared to bent channel with deionized water.

RevDate: 2020-10-06
CmpDate: 2020-10-06

Tang W, Zhu S, Jiang D, et al (2020)

Channel innovations for inertial microfluidics.

Lab on a chip, 20(19):3485-3502.

Inertial microfluidics has gained significant attention since first being proposed in 2007 owing to the advantages of simplicity, high throughput, precise manipulation, and freedom from an external field. Superior performance in particle focusing, filtering, concentrating, and separating has been demonstrated. As a passive technology, inertial microfluidics technology relies on the unconventional use of fluid inertia in an intermediate Reynolds number range to induce inertial migration and secondary flow, which depend directly on the channel structure, leading to particle migration to the lateral equilibrium position or trapping in a specific cavity. With the advances in micromachining technology, many channel structures have been designed and fabricated in the past decade to explore the fundamentals and applications of inertial microfluidics. However, the channel innovations for inertial microfluidics have not been discussed comprehensively. In this review, the inertial particle manipulations and underlying physics in conventional channels, including straight, spiral, sinusoidal, and expansion-contraction channels, are briefly described. Then, recent innovations in channel structure for inertial microfluidics, especially channel pattern modification and unconventional cross-sectional shape, are reviewed. Finally, the prospects for future channel innovations in inertial microfluidic chips are also discussed. The purpose of this review is to provide guidance for the continued study of innovative channel designs to improve further the accuracy and throughput of inertial microfluidics.

RevDate: 2020-09-09

O'Neill G, NS Tolley (2020)

Modelling nasal airflow coefficients: an insight into the nature of airflow.

Rhinology pii:2650 [Epub ahead of print].

BACKGROUND: There has been considerable discussion and conflicting views regarding the presence of laminar or turbulent flow within the nose. The aim of this study was to investigate how the modelling of variable flow coefficients can assist in the evalua- tion of the characteristics of flow in the resistive segments of the nose.

METHODOLOGY: A comparison was made between the flow coefficient for the nasal valve, obtained from a mathematical model, and resistive flow components such as a Venturi meter and orifice tube. Also, a variable loss coefficient was formulated for the whole (unilateral) nose which, by utilising the intersection of the laminar and turbulent asymptotes, provided an estimation for the critical Reynolds number (Rcrit).

RESULTS: The results show that the flow resistance of the nasal valve is considerably greater than that for both a Venturi meter and an orifice tube implying turbulent or turbulent-like flow for much of nasal inspiration. Regarding the loss coefficient for the whole (unilateral) nose, normal respiration flowrates are displaced well away from the laminar asymptote. The critical Reynolds number was estimated to be 450.

CONCLUSIONS: A novel method of determining the flow characteristics of the nose, particularly the critical Reynolds number, is presented. The analysis indicates a higher degree of turbulence than is assumed from a simple traditional calculation using a hy- draulic diameter and flow through straight tubes. There are implications for computational fluid dynamics (CFD) modelling where either the entire nasal airflow is assumed to be laminar or a low turbulence model implemented.

RevDate: 2020-10-07

Tegze G, Podmaniczky F, Somfai E, et al (2020)

Orientational order in dense suspensions of elliptical particles in the non-Stokesian regime.

Soft matter, 16(38):8925-8932.

Suspensions of neutrally buoyant elliptic particles are modeled in 2D using fully resolved simulations that provide two-way interaction between the particle and the fluid medium. Forces due to particle collisions are represented by a diffuse interface approach that allows the investigation of dense suspensions (up to 47% packing fraction). We focus on the role inertial forces play at low and high particle Reynolds numbers termed low Reynolds number and inertial regimes, respectively. The suspensions are characterized by the orientation distribution function (ODF) that reflects shear induced rotation of the particles at low Reynolds numbers, and nearly stationary (swaying) particles at high Reynolds numbers. In both cases, orientational ordering differs qualitatively from the behavior observed in the Stokesian-regime. The ODF becomes flatter with increasing packing fraction, as opposed to the sharpening previous work predicted in the Stokesian regime. The ODF at low particle concentrations differs significantly for the low Reynolds number and inertial regimes, whereas with increasing packing fraction convergence is observed. For dense suspensions, the particle-particle interactions dominate the particle motion.

RevDate: 2020-09-15

Cui G, I Jacobi (2020)

Magnetic Control of Ferrofluid Droplet Adhesion in Shear Flow and on Inclined Surfaces.

Langmuir : the ACS journal of surfaces and colloids, 36(36):10885-10891.

The manipulation of ferrofluidic droplets by magnetic fields is a popular technique for controlling fluid transport in open microfluidic systems. We examine the effect of gravity and shear flow external forces on the adhesion properties of sessile ferrofluidic droplets in the presence of a uniform magnetic field. The magnetic field was found to enhance the critical Bond number at which sliding begins on a tilting substrate but suppress the critical Weber number at which sliding begins in a moderate Reynolds number channel flow. The divergent adhesion trends are explained in terms of the shape deformation induced in the ferrofluidic droplet, the substrate wettability, and the apparent contact angle variation induced by the droplet deformation.

RevDate: 2020-09-03

Xu H, Baroli D, A Veneziani (2020)

Global Sensitivity Analysis for Patient-Specific Aortic Simulations: the Role of Geometry, Boundary Condition and LES Modeling Parameters.

Journal of biomechanical engineering pii:1086637 [Epub ahead of print].

Uncertainties affect the reliability of the numerical simulation of hemodynamics in patient-specific settings and rigorous Uncertainty Quantification (UQ) is in order. This work presents a UQ study on the aorta flow, for assessing the sensitivity of the clinical relevant quantities to the morphology and imprecise knowledge of the inflow boundary condition using the Polynomial Chaos Expansion based Sobol' indices. The geometrical uncertainty is modeled based on a set of longitudinal imaging data of a patient with the abdominal aortic aneurysm. The images of the patient's aorta at different stages of the disease are used to create a map that drives the realistic variation of the reconstructed morphology. The aorta is a peculiar site for hemodynamics, since the flow is highly disturbed due to the high Reynolds number during systole, and the modeling of turbulence helps to avoid the high computational costs. The deconvolution-based Leray model was considered in the past for these simulations. The LES model features problem-dependent numerical parameters to tune. We borrow the same UQ tools used for physical uncertain quantities to assess the sensitivity of the simulations to one of these numerical parameters, the filter radius. The sensitivity of the total kinetic energy, the time average wall shear stress, and the oscillatory shear index are analyzed. The results show that the geometry has the most dominant contribution to the uncertainty of all the quantities of interest. The sensitivity analysis provides confidence intervals for the simulations that quantify the reliability of the numerical predictions.

RevDate: 2020-09-04

Battista F, Mollicone JP, Gualtieri P, et al (2019)

Exact regularized point particle (ERPP) method for particle-laden wall-bounded flows in the two-way coupling regime.

Journal of fluid mechanics, 878:420-444.

The Exact Regularized Point Particle (ERPP) method is extended to treat the interphase momentum coupling between particles and fluid in the presence of walls by accounting for the vorticity generation due to the particles close to solid boundaries. The ERPP method overcomes the limitations of other methods by allowing the simulation of an extensive parameter space (Stokes number, mass loading, particle-to-fluid density ratio and Reynolds number) and of particle spatial distributions that are uneven (few particles per computational cell). The enhanced ERPP method is explained in detail and validated by considering the global impulse balance. In conditions when particles are located close to the wall, a common scenario in wall-bounded turbulent flows, the main contribution to the total impulse arises from the particle-induced vorticity at the solid boundary. The method is applied to direct numerical simulations of particle-laden turbulent pipe flow in the two-way coupling regime to address the turbulence modulation. The effects of the mass loading, the Stokes number and the particle-to-fluid density ratio are investigated. The drag is either unaltered or increased by the particles with respect to the uncoupled case. No drag reduction is found in the parameter space considered. The momentum stress budget, which includes an extra stress contribution by the particles, provides the rationale behind the drag behaviour. The extra stress produces a momentum flux towards the wall that strongly modifies the viscous stress, the culprit of drag at solid boundaries.

RevDate: 2020-09-03

Mottaghi S, Nazari M, Fattahi SM, et al (2020)

Droplet size prediction in a microfluidic flow focusing device using an adaptive network based fuzzy inference system.

Biomedical microdevices, 22(3):61 pii:10.1007/s10544-020-00513-4.

Microfluidics has wide applications in different technologies such as biomedical engineering, chemistry engineering, and medicine. Generating droplets with desired size for special applications needs costly and time-consuming iterations due to the nonlinear behavior of multiphase flow in a microfluidic device and the effect of several parameters on it. Hence, designing a flexible way to predict the droplet size is necessary. In this paper, we use the Adaptive Neural Fuzzy Inference System (ANFIS), by mixing the artificial neural network (ANN) and fuzzy inference system (FIS), to study the parameters which have effects on droplet size. The four main dimensionless parameters, i.e. the Capillary number, the Reynolds number, the flow ratio and the viscosity ratio are regarded as the inputs and the droplet diameter as the output of the ANFIS. Using dimensionless groups cause to extract more comprehensive results and avoiding more experimental tests. With the ANFIS, droplet sizes could be predicted with the coefficient of determination of 0.92.

RevDate: 2020-11-09

McGurk KA, Owen B, Watson WD, et al (2020)

Heritability of haemodynamics in the ascending aorta.

Scientific reports, 10(1):14356.

Blood flow in the vasculature can be characterised by dimensionless numbers commonly used to define the level of instabilities in the flow, for example the Reynolds number, Re. Haemodynamics play a key role in cardiovascular disease (CVD) progression. Genetic studies have identified mechanosensitive genes with causal roles in CVD. Given that CVD is highly heritable and abnormal blood flow may increase risk, we investigated the heritability of fluid metrics in the ascending aorta calculated using patient-specific data from cardiac magnetic resonance (CMR) imaging. 341 participants from 108 British Caucasian families were phenotyped by CMR and genotyped for 557,124 SNPs. Flow metrics were derived from the CMR images to provide some local information about blood flow in the ascending aorta, based on maximum values at systole at a single location, denoted max, and a 'peak mean' value averaged over the area of the cross section, denoted pm. Heritability was estimated using pedigree-based (QTDT) and SNP-based (GCTA-GREML) methods. Estimates of Reynolds number based on spatially averaged local flow during systole showed substantial heritability ([Formula: see text], [Formula: see text]), while the estimated heritability for Reynolds number calculated using the absolute local maximum velocity was not statistically significant (12-13%; [Formula: see text]). Heritability estimates of the geometric quantities alone; e.g. aortic diameter ([Formula: see text], [Formula: see text]), were also substantially heritable, as described previously. These findings indicate the potential for the discovery of genetic factors influencing haemodynamic traits in large-scale genotyped and phenotyped cohorts where local spatial averaging is used, rather than instantaneous values. Future Mendelian randomisation studies of aortic haemodynamic estimates, which are swift to derive in a clinical setting, will allow for the investigation of causality of abnormal blood flow in CVD.

RevDate: 2020-10-22

Nichka VS, Geoffroy TR, Nikonenko V, et al (2020)

Impacts of Flow Rate and Pulsed Electric Field Current Mode on Protein Fouling Formation during Bipolar Membrane Electroacidification of Skim Milk.

Membranes, 10(9):.

Fouling is one of the major problems in electrodialysis. The aim of the present work was to investigate the effect of five different solution flow rates (corresponding to Reynolds numbers of 162, 242, 323, 404 and 485) combined with the use of pulsed electric field (PEF) current mode on protein fouling of bipolar membrane (BPM) during electrodialysis with bipolar membranes (EDBM) of skim milk. The application of PEF prevented the fouling formation by proteins on the cationic interface of the BPM almost completely, regardless of the flow rate or Reynolds number. Indeed, under PEF mode of current the weight of protein fouling was negligible in comparison with CC current mode (0.07 ± 0.08 mg/cm2 versus 5.56 ± 2.40 mg/cm2). When a continuous current (CC) mode was applied, Reynolds number equals or higher than 323 corresponded to a minimal value of protein fouling of BPM. This positive effect of both increasing the flow rate and using PEF is due to the facts that during pauses, the solution flow flushes the accumulated protein from the membrane while in the same time there is a decrease in concentration polarization (CP) and consequently decrease in H+ generation at the cationic interface of the BPM, minimizing fouling formation and accumulation.

RevDate: 2020-10-19

Tripathi D, Prakash J, Tiwari AK, et al (2020)

Thermal, microrotation, electromagnetic field and nanoparticle shape effects on Cu-CuO/blood flow in microvascular vessels.

Microvascular research, 132:104065.

A thermal analysis of Cu-CuO/ blood nanofluids flow in asymmetric microchannel propagating with wave velocity is presented in this study. For the blood, a micropolar fluid model is considered to investigate the microrotation effects of blood flow. Thermal radiation effects and the influence of nanoparticle shape, electric double layer thickness, and electromagnetic fields on the flow are studied. Three types of nanoparticles shapes namely cylinder, bricks and platelets are taken into account. Governing equations are solved under the approximations of long wavelength, low Reynolds number, and Debye-Hückel linearization. Numerical computations are performed for the axial pressure gradient, axial velocity, spin velocity and temperature distribution. The effects of various physical parameters on flow and thermal characteristics are computed and their physical interpretation is also discussed. The outcomes indicate that the axial velocity of Cu-CuO/blood nanoparticles strongly depends on applied electromagnetic field and microrotation. The model's finding will be applicable in designing the smart electromagnetic micro pumps for the hemodialysis and lungs-on-chip devices for the pumping of the blood.

RevDate: 2020-09-28

Zhu L, Xu B, Wu X, et al (2020)

Analysis of volumetric mass transfer coefficient (kLa) in small- (250 mL) to large-scale (2500 L) orbitally shaken bioreactors.

3 Biotech, 10(9):397.

In this study, the combination of dimensional analysis (DA) and analysis of variance (ANOVA) was used to predict the volumetric mass transfer coefficient (kLa) values under different operating conditions for orbitally shaken bioreactors (OSRs) with different filling volumes. It was found that Reynolds number and the interaction between Froude number and geometric number have the largest impact on kLa with impact indexes of 7.41 and 7.50, respectively. Moreover, the volume number has the largest negative impact on kLa, with an impact index of - 5.34. Thus, an effective way to increase the oxygen supply is by increasing the shaking speed and shaking diameter or decreasing the vessel diameter. However, cell cultivation with a higher filling volume will have an increased risk of oxygen scarcity. Therefore, with the help of the kLa prediction model, a suitable operating condition can be determined effectively and easily.

RevDate: 2020-10-30

Ghalambaz M, Arasteh H, Mashayekhi R, et al (2020)

Investigation of Overlapped Twisted Tapes Inserted in a Double-Pipe Heat Exchanger Using Two-Phase Nanofluid.

Nanomaterials (Basel, Switzerland), 10(9): pii:nano10091656.

This study investigated the laminar convective heat transfer and fluid flow of Al2O3 nanofluid in a counter flow double-pipe heat exchanger equipped with overlapped twisted tape inserts in both inner and outer tubes. Two models of the same (co-swirling twisted tapes) and opposite (counter-swirling twisted tapes) angular directions for the stationary twisted tapes were considered. The computational fluid dynamic simulations were conducted through varying the design parameters, including the angular direction of twisted tape inserts, nanofluid volume concentration, and Reynolds number. It was found that inserting the overlapped twisted tapes in the heat exchanger significantly increases the thermal performance as well as the friction factor compared with the plain heat exchanger. The results indicate that models of co-swirling twisted tapes and counter-swirling twisted tapes increase the average Nusselt number by almost 35.2-66.2% and 42.1-68.7% over the Reynolds number ranging 250-1000, respectively. To assess the interplay between heat transfer enhancement and pressure loss penalty, the dimensionless number of performance evaluation criterion was calculated for all the captured configurations. Ultimately, the highest value of performance evaluation criterion is equal to 1.40 and 1.26 at inner and outer tubes at the Reynolds number of 1000 and the volume fraction of 3% in the case of counter-swirling twisted tapes model.

RevDate: 2020-10-07

Zhang S, Cui Z, Wang Y, et al (2020)

Metachronal actuation of microscopic magnetic artificial cilia generates strong microfluidic pumping.

Lab on a chip, 20(19):3569-3581.

Biological cilia that generate fluid flow or propulsion are often found to exhibit a collective wavelike metachronal motion, i.e. neighboring cilia beat slightly out-of-phase rather than synchronously. Inspired by this observation, this article experimentally demonstrates that microscopic magnetic artificial cilia (μMAC) performing a metachronal motion can generate strong microfluidic flows, though, interestingly, the mechanism is different from that in biological cilia, as is found through a systematic experimental study. The μMAC are actuated by a facile magnetic setup, consisting of an array of rod-shaped magnets. This arrangement imposes a time-dependent non-uniform magnetic field on the μMAC array, resulting in a phase difference between the beatings of adjacent μMAC, while each cilium exhibits a two-dimensional whip-like motion. By performing the metachronal 2D motion, the μMAC are able to generate a strong flow in a microfluidic chip, with velocities of up to 3000 μm s-1 in water, which, different from biological cilia, is found to be a result of combined metachronal and inertial effects, in addition to the effect of asymmetric beating. The pumping performance of the metachronal μMAC outperforms all previously reported microscopic artificial cilia, and is competitive with that of most of the existing microfluidic pumping methods, while the proposed platform requires no physical connection to peripheral equipment, reduces the usage of reagents by minimizing "dead volumes", avoids undesirable electrical effects, and accommodates a wide range of different fluids. The 2D metachronal motion can also generate a flow with velocities up to 60 μm s-1 in pure glycerol, where Reynolds number is less than 0.05 and the flow is primarily caused by the metachronal motion of the μMAC. These findings offer a novel solution to not only create on-chip integrated micropumps, but also design swimming and walking microrobots, as well as self-cleaning and antifouling surfaces.

RevDate: 2020-08-27

Latt J, Coreixas C, Beny J, et al (2020)

Efficient supersonic flow simulations using lattice Boltzmann methods based on numerical equilibria.

Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, 378(2175):20190559.

A double-distribution-function based lattice Boltzmann method (DDF-LBM) is proposed for the simulation of polyatomic gases in the supersonic regime. The model relies on a numerical equilibrium that has been extensively used by discrete velocity methods since the late 1990s. Here, it is extended to reproduce an arbitrary number of moments of the Maxwell-Boltzmann distribution. These extensions to the standard 5-constraint (mass, momentum and energy) approach lead to the correct simulation of thermal, compressible flows with only 39 discrete velocities in 3D. The stability of this BGK-LBM is reinforced by relying on Knudsen-number-dependent relaxation times that are computed analytically. Hence, high Reynolds-number, supersonic flows can be simulated in an efficient and elegant manner. While the 1D Riemann problem shows the ability of the proposed approach to handle discontinuities in the zero-viscosity limit, the simulation of the supersonic flow past a NACA0012 aerofoil confirms the excellent behaviour of this model in a low-viscosity and supersonic regime. The flow past a sphere is further simulated to investigate the 3D behaviour of our model in the low-viscosity supersonic regime. The proposed model is shown to be substantially more efficient than the previous 5-moment D3Q343 DDF-LBM for both CPU and GPU architectures. It then opens up a whole new world of compressible flow applications that can be realistically tackled with a purely LB approach. This article is part of the theme issue 'Fluid dynamics, soft matter and complex systems: recent results and new methods'.

RevDate: 2020-10-19

Akram J, Akbar NS, D Tripathi (2020)

Blood-based graphene oxide nanofluid flow through capillary in the presence of electromagnetic fields: A Sutterby fluid model.

Microvascular research, 132:104062.

Pumping devices with the electrokinetics phenomena are important in many microscale transport phenomena in physiology. This study presents a theoretical and numerical investigation on the peristaltic pumping of non-Newtonian Sutterby nanofluid through capillary in presence of electromagnetohydrodynamics. Here blood (Sutterby fluid) is taken as a base fluid and nanofluid is prepared by the suspension of graphene oxide nanoparticle in blood. Graphene oxide is extremely useful in the medical domain for drug delivery and cancer treatment. The modified Buongiorno model for nanofluids and Poisson-Boltzmann ionic distribution is adopted for the formulation of the present problem. Constitutive flow equations are linearized by the implementation of approximations low Reynolds number, large wavelength, and the Debye-Hückel linearization. The numerical solution of reduced coupled and nonlinear set of equations is computed through Mathematica and graphical illustration is presented. Further, the impacts of buoyancy forces, thermal radiation, and mixed convection are also studied. It is revealed in this investigation that the inclusion of a large number of nanoparticles alters the flow characteristics significantly and boosts the heat transfer mechanism. Moreover, the pumping power of the peristaltic pump can be enhanced by the reduction in the width of the electric double layer which can be done by altering the electrolyte concentration.

RevDate: 2020-10-21
CmpDate: 2020-10-21

Moruzzi RB, Campos LC, Sharifi S, et al (2020)

Nonintrusive investigation of large Al-kaolin fractal aggregates with slow settling velocities.

Water research, 185:116287.

Although a combination of aggregate characteristics dictate particle settling, it is commonly assumed that large particles have higher terminal velocities. This simplifying assumption often leads to overprediction of large aggregate settling velocities which in turn negatively impacts on estimates of sedimentation clarification efficiency. Despite its importance, little attention has been given to large aggregates with slow-settling velocities. This paper addresses this gap by investigating slow-settling velocities of large, heterodisperse and multi-shape Al-kaolin aggregates using non-intrusive methods. A particle image velocimetry technique (PIV) was applied to track aggregate velocity and a non-intrusive image technique was used to determine aggregate characteristics, including size (df), three-dimensional fractal dimension (Df), density (ρf), aggregate velocity (Vexp) and Reynolds number (Re). Results showed no strict dependence of settling velocity on large aggregate size, shape and density, as Al-kaolin aggregates with the same size exhibited different settling velocities. A comparison of the results with the well-known Stokes' law for velocity modified by a shape factor showed that the settling velocities measured here can vary from 2 to 14 fold lower than the predicted values for perfect sphere-shape aggregates with the same density and size. Furthermore, results have also shown large Al-kaolin aggregate's drag coefficient (Cd) to be around 56/Re, for average fractal aggregate sphericity of around 0.58.

RevDate: 2020-08-18

Cui J, Liu Y, Xiao L, et al (2020)

Numerical study on the adhesion of a circulating tumor cell in a curved microvessel.

Biomechanics and modeling in mechanobiology pii:10.1007/s10237-020-01380-x [Epub ahead of print].

The adhesion of a circulating tumor cell (CTC) in a three-dimensional curved microvessel was numerically investigated. Simulations were first performed to characterize the differences in the dynamics and adhesion of a CTC in the straight and curved vessels. After that, a parametric study was performed to investigate the effects of the applied driven force density f (or the flow Reynolds number Re) and the CTC membrane bending modulus Kb on the CTC adhesion. Our simulation results show that the CTC prefers to adhere to the curved vessel as more bonds are formed around the transition region of the curved part due to the increased cell-wall contact by the centrifugal force. The parametric study also indicates that when the flow driven force f (or Re) increases or when the CTC becomes softer (Kb decreases), the bond formation probability increases and the bonds will be formed at more sites of a curved vessel. The increased f (or Re) brings a larger centrifugal force, while the decreased Kb generates more contact areas at the cell-wall interface, both of which are beneficial to the bond formation. In the curved vessel, it is found that the site where bonds are formed the most (hotspot) varies with the applied f and the Kb. For our vessel geometry, when f is small, the hotspot tends to be within the first bend of the vessel, while as f increases or Kb decreases, the hotspot may shift to the second bend of the vessel.

RevDate: 2020-09-30

Rao C, H Liu (2020)

Effects of Reynolds number and distribution on passive flow control in owl-inspired leading-edge serrations.

Integrative and comparative biology pii:5893479 [Epub ahead of print].

As a sophisticated micro device for noise reduction, the owl-inspired leading-edge (LE) serrations have been confirmed capable of achieving passive control of laminar-turbulent transition while normally paying a cost of lowering the aerodynamic performance in low Reynolds number (Re∼O(103)) regime. In order to explore potential applications of the owl-inspired serrated airfoils or blades in developing low noise wind turbines or multi-copters normally operating at higher Res, we conducted a large-eddy simulation (LES)-based study of Re effects on the aerodynamic performance of 2D clean and serrated models. Our results show that the LE serrations keep working effectively in mitigating turbulent fluctuations over a broad range of Re (O(103) ∼ O(105)), capable of achieving marked improvement in lift-to-drag ratio with increasing Res. As the aeroacoustic fields are in close association with the propagation of the turbulence sources, it is observed that the tradeoff between passive mitigation of turbulent fluctuations (hence aeroacoustic noise suppression) and aerodynamic performance can be noticeably mitigated at large angles of attack (AoA) and at high Res. This indicates that the LE serrations present an alternative passive flow control mechanism at high Res through a straightforward local excitation of the flow transition while capable of mitigating the turbulent intensity passively. We further developed a 3D LES model of clean and partially serrated rectangular wings to investigate the effects of the LE serrations' distribution on aerodynamic features, on the basis of the observation that longer serrations are often distributed intensively in the mid-span of real owl's feathers. We find that the mid-span distributed LE serrations can facilitate the break-up of leading-edge vortices and the turbulent transition passively and effectively while achieving a low level of turbulence kinetic energy over the upper suction surface of the wing.

RevDate: 2020-09-28

Ardeshiri H, Cassiani M, Park SY, et al (2020)

On the Convergence and Capability of the Large-Eddy Simulation of Concentration Fluctuations in Passive Plumes for a Neutral Boundary Layer at Infinite Reynolds Number.

Boundary-layer meteorology, 176(3):291-327.

Large-eddy simulation (LES) experiments have been performed using the Parallelized LES Model (PALM). A methodology for validating and understanding LES results for plume dispersion and concentration fluctuations in an atmospheric-like flow is presented. A wide range of grid resolutions is shown to be necessary for investigating the convergence of statistical characteristics of velocity and scalar fields. For the scalar, the statistical moments up to the fourth order and the shape of the concentration probability density function (p.d.f.) are examined. The mean concentration is influenced by grid resolution, with the highest resolution simulation showing a lower mean concentration, linked to larger turbulent structures. However, a clear tendency to convergence of the concentration variance is observed at the two higher resolutions. This behaviour is explained by showing that the mechanisms driving the mean and the variance are differently influenced by the grid resolution. The analysis of skewness and kurtosis allows also the obtaining of general results on plume concentration fluctuations. Irrespective of grid resolution, a family of Gamma p.d.f.s well represents the shape of the concentration p.d.f. but only beyond the peak of the concentration fluctuation intensity. In the early plume dispersion phases, the moments of the p.d.f. are in good agreement with those generated by a fluctuating plume model. To the best of our knowledge, our study demonstrates for the first time that, if resolution and averaging time are adequate, atmospheric LES provides a trustworthy representation of the high order moments of the concentration field, up to the fourth order, for a dispersing plume.

RevDate: 2020-08-19

Ryan DP, Chen Y, Nguyen P, et al (2020)

3D particle transport in multichannel microfluidic networks with rough surfaces.

Scientific reports, 10(1):13848.

The transport of particles and fluids through multichannel microfluidic networks is influenced by details of the channels. Because channels have micro-scale textures and macro-scale geometries, this transport can differ from the case of ideally smooth channels. Surfaces of real channels have irregular boundary conditions to which streamlines adapt and with which particle interact. In low-Reynolds number flows, particles may experience inertial forces that result in trans-streamline movement and the reorganization of particle distributions. Such transport is intrinsically 3D and an accurate measurement must capture movement in all directions. To measure the effects of non-ideal surface textures on particle transport through complex networks, we developed an extended field-of-view 3D macroscope for high-resolution tracking across large volumes ([Formula: see text]) and investigated a model multichannel microfluidic network. A topographical profile of the microfluidic surfaces provided lattice Boltzmann simulations with a detailed feature map to precisely reconstruct the experimental environment. Particle distributions from simulations closely reproduced those observed experimentally and both measurements were sensitive to the effects of surface roughness. Under the conditions studied, inertial focusing organized large particles into an annular distribution that limited their transport throughout the network while small particles were transported uniformly to all regions.

RevDate: 2020-08-14
CmpDate: 2020-08-14

Deng D, Pan Y, Liu G, et al (2020)

Seeking the hotspots of nitrogen removal: A comparison of sediment denitrification rate and denitrifier abundance among wetland types with different hydrological conditions.

The Science of the total environment, 737:140253.

Wetlands play a vital role in removing nitrogen (N) from aquatic environments via the denitrification process, which is regulated by multiple environmental and biological factors. Until now, the mechanisms by which environmental factors and microbial abundance regulate denitrification rates in wetlands under different hydrological conditions remain poorly understood. Here, we investigated sediment potential denitrification rate (PDR) and unamended denitrification rate (UDR), and quantified denitrifier abundance (nirS, nirK, and nosZ genes) in 36 stream, river, pond, and ditch wetland sites along the Dan River, a nitrogen-rich river in central China. The result indicated that ditches had the highest denitrification rates and denitrifier abundance. Both PDR and UDR showed strong seasonality, and were observed to be negatively correlated with water velocity in streams and rivers. Moreover, denitrification rates were significantly related to denitrifier abundance and many water quality parameters and sediment properties. Interestingly, PDR and UDR were generally positively associated with N and carbon (C) availability in streams and rivers, but such correlations were not found in ponds and ditches. Using a scaling analysis, we found that environmental parameters, including Reynolds number, sediment total C ratio, and interstitial space, coupled with relative nirS gene abundance could predict the hotspots of denitrification rates in wetlands with varying hydrologic regimes. Our findings highlight that hydrological conditions, especially water velocity and hydrologic pulsing, play a nonnegligible role in determining N biogeochemical processes in wetlands.

RevDate: 2020-09-11

Patterson LHC, Walker JL, Naivar MA, et al (2020)

Inertial flow focusing: a case study in optimizing cellular trajectory through a microfluidic MEMS device for timing-critical applications.

Biomedical microdevices, 22(3):52 pii:10.1007/s10544-020-00508-1.

Although microfluidic micro-electromechanical systems (MEMS) are well suited to investigate the effects of mechanical force on large populations of cells, their high-throughput capabilities cannot be fully leveraged without optimizing the experimental conditions of the fluid and particles flowing through them. Parameters such as flow velocity and particle size are known to affect the trajectories of particles in microfluidic systems and have been studied extensively, but the effects of temperature and buffer viscosity are not as well understood. In this paper, we explored the effects of these parameters on the timing of our own cell-impact device, the μHammer, by first tracking the velocity of polystyrene beads through the device and then visualizing the impact of these beads. Through these assays, we find that the timing of our device is sensitive to changes in the ratio of inertial forces to viscous forces that particles experience while traveling through the device. This sensitivity provides a set of parameters that can serve as a robust framework for optimizing device performance under various experimental conditions, without requiring extensive geometric redesigns. Using these tools, we were able to achieve an effective throughput over 360 beads/s with our device, demonstrating the potential of this framework to improve the consistency of microfluidic systems that rely on precise particle trajectories and timing.

RevDate: 2020-09-30

Waldrop LD, He Y, Hedrick TL, et al (2020)

Functional morphology of gliding flight I. Modeling reveals distinct performance landscapes based on soaring strategies.

Integrative and comparative biology pii:5885086 [Epub ahead of print].

The physics of flight influences the morphology of bird wings through natural selection on flight performance. The connection between wing morphology and performance is unclear due to the complex relationships between various parameters of flight. In order to better understand this connection, we present a holistic analysis of gliding flight that preserves complex relationships between parameters. We use a computational model of gliding flight, along with analysis by uncertainty quantification, to 1) create performance landscapes of gliding based on output metrics (maximum lift-to-drag ratio, minimum gliding angle, minimum sinking speed, lift coefficient at minimum sinking speed); and 2) predict what parameters of flight (chordwise camber, wing aspect ratio, Reynolds number) would differ between gliding and non-gliding species of birds. We also examine performance based on soaring strategy for possible differences in morphology within gliding birds. Gliding birds likely have greater aspect ratios than non-gliding birds, due the high sensitivity of aspect ratio on most metrics of gliding performance. Furthermore, gliding birds can use two distinct soaring strategies based on performance landscapes. First, maximizing distance traveled (maximizing lift-to-drag ratio and minimizing gliding angle) should result in wings with high aspect ratios and middling-to-low wing chordwise camber. Second, maximizing lift extracted from updrafts should result in wings with middling aspect ratios and high wing chordwise camber. Following studies can test these hypotheses using morphological measurements.

RevDate: 2020-08-19

Arrieta J, Cartwright JHE, Gouillart E, et al (2020)

Geometric mixing.

Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, 378(2179):20200168.

Mixing fluids often involves a periodic action, like stirring one's tea. But reciprocating motions in fluids at low Reynolds number, in Stokes flows where inertia is negligible, lead to periodic cycles of mixing and unmixing, because the physics, molecular diffusion excepted, is time reversible. So how can fluid be mixed in such circumstances? The answer involves a geometric phase. Geometric phases are found everywhere in physics as anholonomies, where after a closed circuit in the parameters, some system variables do not return to their original values. We discuss the geometric phase in fluid mixing: geometric mixing. This article is part of the theme issue 'Stokes at 200 (part 2)'.

RevDate: 2020-08-05

Seyler SL, S Pressé (2020)

Surmounting potential barriers: Hydrodynamic memory hedges against thermal fluctuations in particle transport.

The Journal of chemical physics, 153(4):041102.

Recently, trapped-particle experiments have probed the instantaneous velocity of Brownian motion revealing that, at early times, hydrodynamic history forces dominate Stokes damping. In these experiments, nonuniform particle motion is well described by the Basset-Boussinesq-Oseen (BBO) equation, which captures the unsteady Basset history force at a low Reynolds number. Building off of these results, earlier we showed that, at low temperature, BBO particles could exploit fluid inertia in order to overcome potential barriers (generically modeled as a tilted washboard), while its Langevin counter-part could not. Here, we explore the behavior of neutrally buoyant BBO particles at finite temperature for moderate Stokes damping. Remarkably, we find that the transport of particles injected into a bumpy potential with sufficiently high barriers can be completely quenched at intermediate temperatures, whereas itinerancy may be possible above and below that temperature window. This effect is present for both Langevin and BBO dynamics, though these occur over drastically different temperature ranges. Furthermore, hydrodynamic memory mitigates these effects by sustaining initial particle momentum, even in the difficult intermediate temperature regime.

RevDate: 2020-08-05

Romanò F, Türkbay T, HC Kuhlmann (2020)

Lagrangian chaos in steady three-dimensional lid-driven cavity flow.

Chaos (Woodbury, N.Y.), 30(7):073121.

Steady three-dimensional flows in lid-driven cavities are investigated numerically using a high-order spectral-element solver for the incompressible Navier-Stokes equations. The focus is placed on critical points in the flow field, critical limit cycles, their heteroclinic connections, and on the existence, shape, and dependence on the Reynolds number of Kolmogorov-Arnold-Moser (KAM) tori. In finite-length cuboidal cavities at small Reynolds numbers, a thin layer of chaotic streamlines covers all walls. As the Reynolds number is increased, the chaotic layer widens and the complementary KAM tori shrink, eventually undergoing resonances, until they vanish. Accurate data for the location of closed streamlines and of KAM tori are provided, both of which reach very close to the moving lid. For steady periodic Taylor-Görtler vortices in spanwise infinitely extended cavities with a square cross section, chaotic streamlines occupy a large part of the flow domain immediately after the onset of Taylor-Görtler vortices. As the Reynolds number increases, the remaining KAM tori vanish from the Taylor-Görtler vortices, while KAM tori grow in the central region further away from the solid walls.

RevDate: 2020-08-05

Chatterjee S, MK Verma (2020)

Kolmogorov flow: Linear stability and energy transfers in a minimal low-dimensional model.

Chaos (Woodbury, N.Y.), 30(7):073110.

In this paper, we derive a four-mode model for the Kolmogorov flow by employing Galerkin truncation and the Craya-Herring basis for the decomposition of velocity field. After this, we perform a bifurcation analysis of the model. Though our low-dimensional model has fewer modes than past models, it captures the essential features of the primary bifurcation of the Kolmogorov flow. For example, it reproduces the critical Reynolds number for the supercritical pitchfork bifurcation and the flow structures of past works. We also demonstrate energy transfers from intermediate scales to large scales. We perform direct numerical simulations of the Kolmogorov flow and show that our model predictions match the numerical simulations very well.

RevDate: 2020-08-05

Josserand C, Le Berre M, Y Pomeau (2020)

Scaling laws in turbulence.

Chaos (Woodbury, N.Y.), 30(7):073137.

Following the idea that dissipation in turbulence at high Reynolds number is dominated by singular events in space-time and described by solutions of the inviscid Euler equations, we draw the conclusion that in such flows, scaling laws should depend only on quantities appearing in the Euler equations. This excludes viscosity or a turbulent length as scaling parameters and constrains drastically possible analytical pictures of this limit. We focus on the drag law deduced by Newton for a projectile moving quickly in a fluid at rest. Inspired by this Newton's drag force law (proportional to the square of the speed of the moving object in the limit of large Reynolds numbers), which is well verified in experiments when the location of the detachment of the boundary layer is defined, we propose an explicit relationship between the Reynolds stress in the turbulent wake and quantities depending on the velocity field (averaged in time but depending on space). This model takes the form of an integrodifferential equation for the velocity which is eventually solved for a Poiseuille flow in a circular pipe.

RevDate: 2020-08-29

Voglhuber-Brunnmaier T, B Jakoby (2020)

Higher-Order Models for Resonant Viscosity and Mass-Density Sensors.

Sensors (Basel, Switzerland), 20(15):.

Advanced fluid models relating viscosity and density to resonance frequency and quality factor of vibrating structures immersed in fluids are presented. The numerous established models which are ultimately all based on the same approximation are refined, such that the measurement range for viscosity can be extended. Based on the simple case of a vibrating cylinder and dimensional analysis, general models for arbitrary order of approximation are derived. Furthermore, methods for model parameter calibration and the inversion of the models to determine viscosity and/or density from measured resonance parameters are shown. One of the two presented fluid models is a viscosity-only model, where the parameters of it can be calibrated without knowledge of the fluid density. The models are demonstrated for a tuning fork-based commercial instrument, where maximum deviations between measured and reference viscosities of approximately ±0.5% in the viscosity range from 1.3 to 243 mPas could be achieved. It is demonstrated that these results show a clear improvement over the existing models.

RevDate: 2020-10-05

Manchester EL, XY Xu (2020)

The effect of turbulence on transitional flow in the FDA's benchmark nozzle model using large-eddy simulation.

International journal for numerical methods in biomedical engineering, 36(10):e3389.

The Food and Drug Administration's (FDA) benchmark nozzle model has been studied extensively both experimentally and computationally. Although considerable efforts have been made on validations of a variety of numerical models against available experimental data, the transitional flow cases are still not fully resolved, especially with regards to detailed comparison of predicted turbulence quantities with experimental measurements. This study aims to fill this gap by conducting large-eddy simulations (LES) of flow through the FDA's benchmark model, at a transitional Reynolds number of 2000. Numerical results are compared to previous interlaboratory experimental results, with an emphasis on turbulence characteristics. Our results show that the LES methodology can accurately capture laminar quantities throughout the model. In the pre-jet breakdown region, predicted turbulence quantities are generally larger than high resolution experimental data acquired with laser Doppler velocimetry. In the jet breakdown regions, where maximum Reynolds stresses occur, Reynolds shear stresses show excellent agreement. Differences of up to 4% and 20% are observed near the jet core in the axial and radial normal Reynolds stresses, respectively. Comparisons between viscous and Reynolds shear stresses show that peak viscous shear stresses occur in the nozzle throat reaching a value of 18 Pa in the boundary layer, whilst peak Reynolds shear stresses occur in the jet breakdown region reaching a maximum value of 87 Pa. Our results highlight the importance in considering both laminar and turbulent contributions towards shear stresses and that neglecting the turbulence effect can significantly underestimate the total shear force exerted on the fluid.

RevDate: 2020-09-15

Ahmed R, Ali N, Al-Khaled K, et al (2020)

Finite difference simulations for non-isothermal hydromagnetic peristaltic flow of a bio-fluid in a curved channel: Applications to physiological systems.

Computer methods and programs in biomedicine, 195:105672.

Owing to the fundamental significances of peristalsis phenomenon in various biological systems like circulation of blood in vessels, lungs devices, pumping of blood in heart and movement of chyme in the gastrointestinal tract, variety of research by scientist on this topic has been presented in recently years. The peristaltic pumping plays a novel role in various industrial processes like transfer of sanitary materials, the pumping equipment design of roller pumps and many more. The present article investigates numerically the theoretical aspects of heat and mass transportation in peristaltic pattern of Carreau fluid through a curved channel. The computations for axial velocity, pressure rise, temperature field, mass concentration, and stream function are carried out under low Reynolds number and long wavelength approximation in the wave frame of reference by utilizing appropriate numerical implicit finite difference technique (FDM). The implementation of numerical procedure and graphical representation of the computations are accomplished using MATLAB language. The impacts of rheological parameters of Carreau fluid, Brinkmann number, curvature parameter and Hartmann number are shown and discussed briefly. The study shows that for shear thinning of bio-materials, the velocity exhibits the boundary layer character near the boundary walls for greater Hartmann number. The interesting observations based on numerical simulations are graphically elaborated. The results show that the curvature of channel with larger value allows more heat transportation within the flow domain. On the contrary, inside the channel wall, the solutal mass concentration follows an increasing trend with decreasing the channel curvature. The temperature profile enhanced with increment of power-law index and curvature parameter. Moreover, the concentration profile increases with Brinkmann number and Hartmann number.

RevDate: 2020-08-01

Boukharfane R, Parsani M, J Bodart (2020)

Characterization of pressure fluctuations within a controlled-diffusion blade boundary layer using the equilibrium wall-modelled LES.

Scientific reports, 10(1):12735 pii:10.1038/s41598-020-69671-y.

In this study, the generation of airfoil trailing edge broadband noise that arises from the interaction of turbulent boundary layer with the airfoil trailing edge is investigated. The primary objectives of this work are: (i) to apply a wall-modelled large-eddy simulation (WMLES) approach to predict the flow of air passing a controlled-diffusion blade, and (ii) to study the blade broadband noise that is generated from the interaction of a turbulent boundary layer with a lifting surface trailing edge. This study is carried out for two values of the Mach number, [Formula: see text] and 0.5, two values of the chord Reynolds number, [Formula: see text] and [Formula: see text], and two angles of attack, AoA [Formula: see text] and [Formula: see text]. To examine the influence of the grid resolution on aerodynamic and aeroacoustic quantities, we compare our results with experimental data available in the literature. We also compare our results with two in-house numerical solutions generated from two wall-resolved LES (WRLES) calculations, one of which has a DNS-like resolution. We show that WMLES accurately predicts the mean pressure coefficient distribution, velocity statistics (including the mean velocity), and the traces of Reynolds tensor components. Furthermore, we observe that the instantaneous flow structures computed by the WMLES resemble those found in the reference WMLES database, except near the leading edge region. Some of the differences observed in these structures are associated with tripping and the transition to a turbulence mechanism near the leading edge, which are significantly affected by the grid resolution. The aeroacoustic noise calculations indicate that the power spectral density profiles obtained using the WMLES compare well with the experimental data.

RevDate: 2020-09-28

Wang Y, Zhang Y, Qiao Z, et al (2020)

A 3D Printed Jet Mixer for Centrifugal Microfluidic Platforms.

Micromachines, 11(7):.

Homogeneous mixing of microscopic volume fluids at low Reynolds number is of great significance for a wide range of chemical, biological, and medical applications. An efficient jet mixer with arrays of micronozzles was designed and fabricated using additive manufacturing (three-dimensional (3D) printing) technology for applications in centrifugal microfluidic platforms. The contact surface of miscible liquids was enhanced significantly by impinging plumes from two opposite arrays of micronozzles to improve mixing performance. The mixing efficiency was evaluated and compared with the commonly used Y-shaped micromixer. Effective mixing in the jet mixer was achieved within a very short timescale (3s). This 3D printed jet mixer has great potential to be implemented in applications by being incorporated into multifarious 3D printing devices in microfluidic platforms.

RevDate: 2020-09-07

Emami MS, Haghshenasfard M, Zarghami R, et al (2020)

Experimental study on the reduction of loratadine particle size through confined liquid impinging jets.

International journal of pharmaceutics, 587:119668.

The confined liquid impinging jets (CLIJ) technique was applied as a simple and effective approach to reducing the particle size of loratadine to enhance its solubility. The effect of anti-solvent (AS) to solution (S) flow rate ratio, organic phase concentration, Reynolds number (Re), and stabilizer concentration was investigated in this reduction process. After the synthesis, the chemical and physical properties of loratadine nanoparticles were determined through different characterization and analytical techniques. The results indicated that the particle size of loratadine decreases from 320 nm to 80 nm by increasing the AS/S ratio from 1 to 25. It was found that the particle size of loratadine was unchanged at the higher AS/S ratios. The loratadine nanoparticle size was optimized by changing the solution concentration, Re, and Tween 80 as a stabilizer. The finest loratadine nanoparticle size of about 53 nm was obtained with a narrow size distribution, which corresponds to solution concentration of 35 mg/mL, Re of 5687, and 0.1% (w/v) stabilizer concentration. It was revealed that the optimized loratadine nanoparticles completely dissolved after 11 min, indicating the loratadine nanoparticle dissolution rate 50 times faster than raw loratadine.

RevDate: 2020-07-21

Fouxon I, C Lee (2020)

Large deviations, singularity, and lognormality of energy dissipation in turbulence.

Physical review. E, 101(6-1):061101.

We study implications of the assumption of power-law dependence of moments of energy dissipation in turbulence on the Reynolds number Re, holding due to intermittency. We demonstrate that at Re→∞ the dissipation's logarithm divided by lnRe converges with probability one to a negative constant. This implies that the dissipation is singular in the limit, as is known phenomenologically. The proof uses a large deviations function, whose existence is implied by the power-law assumption, and which provides the general asymptotic form of the dissipation's distribution. A similar function exists for vorticity and for velocity differences where it proves the moments representation of the multifractal model (MF). Then we observe that derivative of the scaling exponents of the dissipation, considered as a function of the order of the moment, is small at the origin. Thus the variation with the order is slow and can be described by a quadratic function. Indeed, the quadratic function, which corresponds to log-normal statistics, fits the data. Moreover, combining the lognormal scaling with the MF we derive a formula for the anomalous scaling exponents of turbulence which also fits the data. Thus lognormality, not to be confused with the Kolmogorov (1962) assumption of lognormal dissipation in the inertial range, when used in conjunction with the MF provides a concise way to get all scaling exponents of turbulence available at present.

RevDate: 2020-07-21

Morita T, Omori T, Nakayama Y, et al (2020)

Harnessing random low Reynolds number flow for net migration.

Physical review. E, 101(6-1):063101.

Random noise in low Reynolds number flow has rarely been used to obtain net migration of microscale objects. In this study, we numerically show that net migration of a microscale object can be extracted from random directional fluid forces in Stokes flow, by introducing deformability and inhomogeneous density into the object. We also developed a mathematical framework to describe the deformation-induced migration caused by noise. These results provide a basis for understanding the noise-induced migration of a microswimmer and are useful for harnessing energy from low Reynolds number flow.

RevDate: 2020-09-28

Askar AH, Kadham SA, SH Mshehid (2020)

The surfactants effect on the heat transfer enhancement and stability of nanofluid at constant wall temperature.

Heliyon, 6(7):e04419 pii:e04419.

Surfactants role in the enhancement of the heat transfer and stability of alumina oxide - distilled water nanofluid was introduced in this research, where there are limited studies that conjugate between the stability improvement and its effect on the heat transfer coefficients. Four weight concentrations for the experiment were used (0.1, 0.3, 0.6, and 0.9%) with 20 nm particle size under a constant wall temperature. The selection of appropriate surfactants weight was tested too by implementing three weight concentrations (0.5, 1, 1.5, and 2 %) related to each nanofluid concentration via measuring their effect on the zeta potential value. The heat transfer augmentation was tested through a double horizontal pipe under a constant wall temperature at entrance region with Reynolds number range (4000-11800). The results manifested the use of nanofluid worked on enhancement the heat transfer performance better than water, and the stable nanofluid elucidated better results.

RevDate: 2020-09-22
CmpDate: 2020-09-22

Yang T, Sprinkle B, Guo Y, et al (2020)

Reconfigurable microbots folded from simple colloidal chains.

Proceedings of the National Academy of Sciences of the United States of America, 117(31):18186-18193.

To overcome the reversible nature of low-Reynolds-number flow, a variety of biomimetic microrobotic propulsion schemes and devices capable of rapid transport have been developed. However, these approaches have been typically optimized for a specific function or environment and do not have the flexibility that many real organisms exhibit to thrive in complex microenvironments. Here, inspired by adaptable microbes and using a combination of experiment and simulation, we demonstrate that one-dimensional colloidal chains can fold into geometrically complex morphologies, including helices, plectonemes, lassos, and coils, and translate via multiple mechanisms that can be varied with applied magnetic field. With chains of multiblock asymmetry, the propulsion mode can be switched from bulk to surface-enabled, mimicking the swimming of microorganisms such as flagella-rotating bacteria and tail-whipping sperm and the surface-enabled motion of arching and stretching inchworms and sidewinding snakes. We also demonstrate that reconfigurability enables navigation through three-dimensional and narrow channels simulating capillary blood vessels. Our results show that flexible microdevices based on simple chains can transform both shape and motility under varying magnetic fields, a capability we expect will be particularly beneficial in complex in vivo microenvironments.

RevDate: 2020-07-20

Ma Y, Zhang M, H Luo (2020)

Numerical and experimental studies of gas-liquid flow and pressure drop in multiphase pump valves.

Science progress, 103(3):36850420940885.

A numerical and experimental study was carried out to investigate the two-phase flow fields of the typical three valves used in the multiphase pumps. Under the gas volume fraction conditions in the range of 0%-100%, the three-dimensional steady and dynamic two-phase flow characteristics, pressure drops, and their multipliers of the ball valve, cone valve, and disk valve were studied, respectively, using Eulerian-Eulerian approach and dynamic grid technique in ANSYS FLUENT. In addition, a valve test system was built to verify the simulated results by the particle image velocimetry and pressure test. The flow coefficient CQ (about 0.989) of the disk valve is greater than those of the other valves (about 0.864) under the steady flow with a high Reynolds number. The two-phase pressure drops of the three valves fluctuate in different forms with the vibration of the cores during the dynamic opening. The two-phase multipliers of the fully opened ball valve are consistent with the predicted values of the Morris model, while those of the cone valve and disk valve had the smallest differences with the predicted values of the Chisholm model. Through the comprehensive analysis of the flow performance, pressure drop, and dynamic stability of the three pump valves, the disk valve is found to be more suitable for the multiphase pumps due to its smaller axial space, resistance loss, and better flow capacity.

RevDate: 2020-09-28

Juraeva M, DJ Kang (2020)

Mixing Performance of a Cross-Channel Split-and-Recombine Micro-Mixer Combined with Mixing Cell.

Micromachines, 11(7):.

A new cross-channel split-and-recombine (CC-SAR) micro-mixer was proposed, and its performance was demonstrated numerically. A numerical study was carried out over a wide range of volume flow rates from 3.1 μL/min to 826.8 μL/min. The corresponding Reynolds number ranges from 0.3 to 80. The present micro-mixer consists of four mixing units. Each mixing unit is constructed by combining one split-and-recombine (SAR) unit with a mixing cell. The mixing performance was analyzed in terms of the degree of mixing and relative mixing cost. All numerical results show that the present micro-mixer performs better than other micro-mixers based on SARs over a wide range of volume flow rate. The mixing enhancement is realized by a particular motion of vortex flow: the Dean vortex in the circular sub-channel and another vortex inside the mixing cell. The two vortex flows are generated on the different planes perpendicular to each other. They cause the two fluids to change their relative position as the fluids flow into the circular sub-channel of the SAR, eventually promoting violent mixing. High vorticity in the mixing cell elongates the flow interface between two fluids, and promotes mixing in the flow regime of molecular diffusion dominance.

RevDate: 2020-10-11

Liu J, Yang W, Dong M, et al (2020)

The nested block preconditioning technique for the incompressible Navier-Stokes equations with emphasis on hemodynamic simulations.

Computer methods in applied mechanics and engineering, 367:.

We develop a novel iterative solution method for the incompressible Navier-Stokes equations with boundary conditions coupled with reduced models. The iterative algorithm is designed based on the variational multiscale formulation and the generalized-α scheme. The spatiotemporal discretization leads to a block structure of the resulting consistent tangent matrix in the Newton-Raphson procedure. As a generalization of the conventional block preconditioners, a three-level nested block preconditioner is introduced to attain a better representation of the Schur complement, which plays a key role in the overall algorithm robustness and efficiency. This approach provides a flexible, algorithmic way to handle the Schur complement for problems involving multiscale and multiphysics coupling. The solution method is implemented and benchmarked against experimental data from the nozzle challenge problem issued by the US Food and Drug Administration. The robustness, efficiency, and parallel scalability of the proposed technique are then examined in several settings, including moderately high Reynolds number flows and physiological flows with strong resistance effect due to coupled downstream vasculature models. Two patient-specific hemodynamic simulations, covering systemic and pulmonary flows, are performed to further corroborate the efficacy of the proposed methodology.

RevDate: 2020-09-24

Xue Y, Hellmuth R, DH Shin (2020)

Formation of Vortices in Idealised Branching Vessels: A CFD Benchmark Study.

Cardiovascular engineering and technology, 11(5):544-559.

PURPOSE: Atherosclerosis preferentially occurs near the junction of branching vessels, where blood recirculation tends to occur (Malek et al. in J Am Med Assoc 282(21):2035-2042, 1999, https://doi.org/10.1001/jama.282.21.2035). For decades, CFD has been used to predict flow patterns such as separation and recirculation zones in hemodynamic models, but those predictions have rarely been validated with experimental data. In the context of verification and validation (V&V), we first conduct a CFD benchmark calculation that reproduces the vortex detection experiments of Karino and Goldsmith (1980) with idealised branching blood vessels (Karino and Goldsmith in Trans. Am. Soc. Artif. Internal Organs 26:500-506, 1980). The critical conditions for the formation of recirculation vortices, the so-called critical Reynolds numbers, are the main parameters for comparison with the experimental data to demonstrate the credibility of the CFD workflow. We then characterise the wall shear stresses and develop a surrogate model for the size of formed vortices.

METHODS: An automated parametric study generating more than 12,000 CFD simulations was performed, sweeping the geometries and flow conditions found in the experiments by Karino and Goldsmith. The flow conditions were restricted to steady-state laminar flow, with a range of inflow Reynolds numbers up to 350, with various flow ratios between the main branch outlet and side branch outlet. The side branch diameter was scaled relative to the main branch diameter, ranging from 1.05/3 to 3/3; and the branching angles ranged in size from [Formula: see text] to [Formula: see text]. Recirculation vortices were detected by the inversion of the velocity vector at certain locations, as well as by the inversion of the wall shear stress (WSS) vector.

RESULTS: The CFD simulations demonstrated good agreement with the experimental data on the critical Reynolds numbers. The spatial distributions of WSS on each branch were analysed to identify potential regions of disease. Once a vortex is formed, the size of the vortex increases by the square root of the Reynolds number. The CFD data was fitted to a surrogate model that accurately predicts the vortex size without the need to run computationally more expensive CFD simulations.

CONCLUSIONS: This benchmark study validates the CFD simulation of vortex detection in idealised branching vessels under comprehensive flow conditions. This work also proposes a surrogate model for the size of the vortex, which could reduce the computational requirements in the studies related to branching vessels and complex vascular systems.

RevDate: 2020-10-30
CmpDate: 2020-10-30

Forte P, Morais JE, P Neiva H, et al (2020)

The Drag Crisis Phenomenon on an Elite Road Cyclist-A Preliminary Numerical Simulations Analysis in the Aero Position at Different Speeds.

International journal of environmental research and public health, 17(14):.

The drag crisis phenomenon is the drop of drag coefficient (Cd) with increasing Reynolds number (Re) or speed. The aim of this study was to assess the hypothetical drag crisis phenomenon in a sports setting, assessing it in a bicycle-cyclist system. A male elite-level cyclist was recruited for this research and his competition bicycle, helmet, suit, and shoes were used. A three-dimensional (3D) geometry was obtained with a 3D scan with the subject in a static aero position. A domain with 7 m of length, 2.5 m of width and 2.5 m of height was created around the cyclist. The domain was meshed with 42 million elements. Numerical simulations by computer fluid dynamics (CFD) fluent numerical code were conducted at speeds between 1 m/s and 22 m/s, with increments of 1 m/s. The drag coefficient ranged between 0.60 and 0.95 across different speeds and Re. The highest value was observed at 2 m/s (Cd = 0.95) and Re of 3.21 × 105, whereas the lower Cd was noted at 9 m/s (Cd = 0.60) and 9.63 × 105. A drag crisis was noted between 3 m/s and 9 m/s. Pressure Cd ranged from 0.35 to 0.52 and the lowest value was observed at 3 m/s and the highest at 2 m/s. The viscous drag coefficient ranged between 0.15 and 0.43 and presented a trend decreasing from 4 m/s to 22 m/s. Coaches, cyclists, researchers, and support staff must consider that Cd varies with speed and Re, and the bicycle-cyclist dimensions, shape, or form may affect drag and performance estimations. As a conclusion, this preliminary work noted a drag crisis between 3 m/s and 9 m/s in a cyclist in the aero position.

RevDate: 2020-09-28

Granados-Ortiz FJ, J Ortega-Casanova (2020)

Mechanical Characterisation and Analysis of a Passive Micro Heat Exchanger.

Micromachines, 11(7):.

Heat exchangers are widely used in many mechanical, electronic, and bioengineering applications at macro and microscale. Among these, the use of heat exchangers consisting of a single fluid passing through a set of geometries at different temperatures and two flows in T-shape channels have been extensively studied. However, the application of heat exchangers for thermal mixing over a geometry leading to vortex shedding has not been investigated. This numerical work aims to analyse and characterise a heat exchanger for microscale application, which consists of two laminar fluids at different temperature that impinge orthogonally onto a rectangular structure and generate vortex shedding mechanics that enhance thermal mixing. This work is novel in various aspects. This is the first work of its kind on heat transfer between two fluids (same fluid, different temperature) enhanced by vortex shedding mechanics. Additionally, this research fully characterise the underlying vortex mechanics by accounting all geometry and flow regime parameters (longitudinal aspect ratio, blockage ratio and Reynolds number), opposite to the existing works in the literature, which usually vary and analyse blockage ratio or longitudinal aspect ratio only. A relevant advantage of this heat exchanger is that represents a low-Reynolds passive device, not requiring additional energy nor moving elements to enhance thermal mixing. This allows its use especially at microscale, for instance in biomedical/biomechanical and microelectronic applications.

RevDate: 2020-09-28

Dai X, Liu C, Zhao J, et al (2020)

Optimization of Application Conditions of Drag Reduction Agent in Product Oil Pipelines.

ACS omega, 5(26):15931-15935.

Drag reduction performance was studied with a rotating disk instrument in the laboratory, and experiments show that there is an initial rapid growth stage and stability stage for drag reduction ratio change. The higher the rotational speed, the larger the initial drag reduction ratio is; the larger the concentration, the shorter the drag reduction stabilization time is. Under high concentration and high speed, the drag reduction onset time is short. Because of the shear degradation, the Reynolds number should be taken into account during use. Through a comparison of diesel properties after adding agents with national standard, it is confirmed that drag reduction agents could be used in this pipeline.

RevDate: 2020-07-08

Pusztai I, Juno J, Brandenburg A, et al (2020)

Dynamo in Weakly Collisional Nonmagnetized Plasmas Impeded by Landau Damping of Magnetic Fields.

Physical review letters, 124(25):255102.

We perform fully kinetic simulations of flows known to produce dynamo in magnetohydrodynamics (MHD), considering scenarios with low Reynolds number and high magnetic Prandtl number, relevant for galaxy cluster scale fluctuation dynamos. We find that Landau damping on the electrons leads to a rapid decay of magnetic perturbations, impeding the dynamo. This collisionless damping process operates on spatial scales where electrons are nonmagnetized, reducing the range of scales where the magnetic field grows in high magnetic Prandtl number fluctuation dynamos. When electrons are not magnetized down to the resistive scale, the magnetic energy spectrum is expected to be limited by the scale corresponding to magnetic Landau damping or, if smaller, the electron gyroradius scale, instead of the resistive scale. In simulations we thus observe decaying magnetic fields where resistive MHD would predict a dynamo.

RevDate: 2020-07-03

Silverberg O, Demir E, Mishler G, et al (2020)

Realization of a Push-Me-Pull-You swimmer at low Reynolds numbers.

Bioinspiration & biomimetics [Epub ahead of print].

Locomotion at low Reynolds numbers encounters stringent physical constraints due to the dominance of viscous over inertial forces. A variety of swimming microorganisms has demonstrated diverse strategies to generate self-propulsion in the absence of inertia. In particular, ameboid and euglenoid movements exploit shape deformations of the cell body for locomotion. Inspired by these biological organisms, the "Push-Me-Pull-You" (PMPY) swimmer (Avron JE, Kenneth O, Oaknin DH 2005 New J. Phys., 7, 234) represents an elegant artificial swimmer that can escape from the constraints of the scallop theorem and generate self-propulsion in highly viscous fluid environments. In this work, we present the first experimental realization of the PMPY swimmer, which consists of a pair of expandable spheres connected by an extensible link. We designed and constructed robotic PMPY swimmers and characterized their propulsion performance in highly viscous silicone oil in dynamically similar, macroscopic experiments. The proof-of-concept demonstrates the feasibility and robustness of the PMPY mechanism as a viable locomotion strategy at low Reynolds numbers.

RevDate: 2020-09-30

Kashima Y, S Ninomiya (2020)

Hemodialysis efficiency management from the viewpoint of blood removal pressure.

Therapeutic apheresis and dialysis : official peer-reviewed journal of the International Society for Apheresis, the Japanese Society for Apheresis, the Japanese Society for Dialysis Therapy [Epub ahead of print].

Degradation of dialysis efficiency during hemodialysis, caused by incompatible indwelling needle size or increase in hematocrit, is a serious problem that can threaten a patient's life. This study aims to derive a quantitative index for determining the indwelling needle diameter that can maintain an appropriate blood flow rate, and presents an effective method to prevent a decrease in the actual blood flow rate. The relationships between the set flow rate and various parameters such as indwelling needle diameter, blood viscosity, and arterial line pressure are analyzed. A simple and reliable method for estimating the actual blood flow rate is derived from these relationships. A correlation between viscosity and actual blood flow rate is estimated adequately by regression analysis using a least-squares method. The relationship between Reynolds number and the flow rate reduction ratio is also evaluated. A new parameter (simple estimation method for actual blood flow) is derived by measuring the blood removal pressure. A pump control approach that uses blood removal pressure is suggested, which can be a future research direction in the field of hemodialysis.

RevDate: 2020-07-02

Zhou T, Zhang X, S Zhong (2020)

An experimental study of trailing edge noise from a heaving airfoil.

The Journal of the Acoustical Society of America, 147(6):4020.

In this study, the far-field noise and near-field flow properties from a heaving NACA 0012 airfoil at the Reynolds number of 6.6×104 were investigated experimentally in a 0.4 m2 anechoic wind tunnel. The airfoil had an incident angle of 0° and followed a sinusoidal heaving motion. The Strouhal number, controlled by changing the heaving frequency and amplitude, varied from 0.0024 to 0.008. The acoustic properties were measured by a free-field microphone placed at a distance of 1.2 m away from the tunnel central line, and the flow structures near the trailing edge were acquired using the particle image velocimetry. It was found that the heaving motion could reduce the sound pressure level (SPL) of the primary peak in the time-averaged spectra. The spectrograms obtained by the short-time Fourier transform revealed that the discrete tones were produced when the airfoil passed through the maximum heaving position. During the corresponding period, a sequence of large-scaled vortices convected on the airfoil surface was observed, and then was shed from the trailing edge to the wake region at the same frequency as the primary tone of the induced sound. With the increase of Strouhal number, the sound signals tended to be broadband, and the overall SPL was increased in the far field.

RevDate: 2020-07-01

Xu W, Luo W, Wang Y, et al (2020)

Data-driven three-dimensional super-resolution imaging of a turbulent jet flame using a generative adversarial network.

Applied optics, 59(19):5729-5736.

Three-dimensional (3D) computed tomography (CT) is becoming a well-established tool for turbulent combustion diagnostics. However, the 3D CT technique suffers from contradictory demands of spatial resolution and domain size. This work therefore reports a data-driven 3D super-resolution approach to enhance the spatial resolution by two times along each spatial direction. The approach, named 3D super-resolution generative adversarial network (3D-SR-GAN), builds a generator and a discriminator network to learn the topographic information and infer high-resolution 3D turbulent flame structure with a given low-resolution counterpart. This work uses numerically simulated 3D turbulent jet flame structures as training data to update model parameters of the GAN network. Extensive performance evaluations are then conducted to show the superiority of the proposed 3D-SR-GAN network, compared with other direct interpolation methods. The results show that a convincing super-resolution (SR) operation with the overall error of ∼4% and the peak signal-to-noise ratio of 37 dB can be reached with an upscaling factor of 2, representing an eight times enhancement of the total voxel number. Moreover, the trained network can predict the SR structure of the jet flame with a different Reynolds number without retraining the network parameters.

RevDate: 2020-06-30

Moum JN (2020)

Variations in Ocean Mixing from Seconds to Years.

Annual review of marine science [Epub ahead of print].

Over the past several decades, there has developed a community-wide appreciation for the importance of mixing at the smallest scales to geophysical fluid dynamics on all scales. This appreciation has spawned greater participation in the investigation of ocean mixing and new ways to measure it. These are welcome developments given the tremendous separation in scales between the basins, 𝒪(107) m, and the turbulence, 𝒪 (10-2) m, and the fact that turbulence that leads to thermodynamically irreversible mixing in high-Reynolds-number geophysical flows varies by at least eight orders of magnitude in both space and time. In many cases, it is difficult to separate the dependencies because measurements are sparse, also in both space and time. Comprehensive shipboard turbulence profiling experiments supplemented by Doppler sonar current measurements provide detailed observations of the evolution of the vertical structure of upper-ocean turbulence on timescales of minutes to weeks. Recent technical developments now permit measurements of turbulence in the ocean, at least at a few locations, for extended periods. This review summarizes recent and classic results in the context of our expanding knowledge of the temporal variability of ocean mixing, beginning with a discussion of the timescales of the turbulence itself (seconds to minutes) and how turbulence-enhanced mixing varies over hours, days, tidal cycles, monsoons, seasons, and El Niño-Southern Oscillation timescales (years). Expected final online publication date for the Annual Review of Marine Science, Volume 13 is January 3, 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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ESP Quick Facts

ESP Origins

In the early 1990's, Robert Robbins was a faculty member at Johns Hopkins, where he directed the informatics core of GDB — the human gene-mapping database of the international human genome project. To share papers with colleagues around the world, he set up a small paper-sharing section on his personal web page. This small project evolved into The Electronic Scholarly Publishing Project.

ESP Support

In 1995, Robbins became the VP/IT of the Fred Hutchinson Cancer Research Center in Seattle, WA. Soon after arriving in Seattle, Robbins secured funding, through the ELSI component of the US Human Genome Project, to create the original ESP.ORG web site, with the formal goal of providing free, world-wide access to the literature of classical genetics.

ESP Rationale

Although the methods of molecular biology can seem almost magical to the uninitiated, the original techniques of classical genetics are readily appreciated by one and all: cross individuals that differ in some inherited trait, collect all of the progeny, score their attributes, and propose mechanisms to explain the patterns of inheritance observed.

ESP Goal

In reading the early works of classical genetics, one is drawn, almost inexorably, into ever more complex models, until molecular explanations begin to seem both necessary and natural. At that point, the tools for understanding genome research are at hand. Assisting readers reach this point was the original goal of The Electronic Scholarly Publishing Project.

ESP Usage

Usage of the site grew rapidly and has remained high. Faculty began to use the site for their assigned readings. Other on-line publishers, ranging from The New York Times to Nature referenced ESP materials in their own publications. Nobel laureates (e.g., Joshua Lederberg) regularly used the site and even wrote to suggest changes and improvements.

ESP Content

When the site began, no journals were making their early content available in digital format. As a result, ESP was obliged to digitize classic literature before it could be made available. For many important papers — such as Mendel's original paper or the first genetic map — ESP had to produce entirely new typeset versions of the works, if they were to be available in a high-quality format.

ESP Help

Early support from the DOE component of the Human Genome Project was critically important for getting the ESP project on a firm foundation. Since that funding ended (nearly 20 years ago), the project has been operated as a purely volunteer effort. Anyone wishing to assist in these efforts should send an email to Robbins.

ESP Plans

With the development of methods for adding typeset side notes to PDF files, the ESP project now plans to add annotated versions of some classical papers to its holdings. We also plan to add new reference and pedagogical material. We have already started providing regularly updated, comprehensive bibliographies to the ESP.ORG site.

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Papers in Classical Genetics

The ESP began as an effort to share a handful of key papers from the early days of classical genetics. Now the collection has grown to include hundreds of papers, in full-text format.

Digital Books

Along with papers on classical genetics, ESP offers a collection of full-text digital books, including many works by Darwin (and even a collection of poetry — Chicago Poems by Carl Sandburg).

Timelines

ESP now offers a much improved and expanded collection of timelines, designed to give the user choice over subject matter and dates.

Biographies

Biographical information about many key scientists.

Selected Bibliographies

Bibliographies on several topics of potential interest to the ESP community are now being automatically maintained and generated on the ESP site.

ESP Picks from Around the Web (updated 07 JUL 2018 )