Evolution of turbulence and in-plane vortices in the near field flow behind multi-scale planar grids
In this experimental work, we carry out detailed two-dimensional particle imagevelocimetry investigations for the near field wakes behind a conventional and two multi-scale planar grids, using stitchedcamera fields of view. Statistical independentmeasurements are conducted focusing on the first few mesh distances downstream of the grid. It is found that the multiple integral length scales originated from the grids loose their importance on theturbulence development after about three mesh distances downstream, much earlier than the distance where theturbulence becomes homogeneous. The largest eddy size, represented by the i...
Source: Physics of Fluids - August 8, 2016 Category: Physics Authors: L. Gan and P.- Å. Krogstad Source Type: research
Nanoscale roughness effect on Maxwell-like boundary conditions for the Boltzmann equation
It is well known that the roughness of the wall has an effect on microscale gas flows. This effect can be shown for large Knudsen numbers by using a numerical solution of theBoltzmann equation. However, when the wall is rough at a nanometric scale, it is necessary to use a very small mesh size which is much too expansive. An alternative approach is to incorporate the roughness effect in thescattering kernel of theboundary condition, such as theMaxwell-like kernel introduced by the authors in a previous paper. Here, we explain how thisboundary condition can be implemented in a discrete velocity approximation of theBoltzmann...
Source: Physics of Fluids - August 5, 2016 Category: Physics Authors: S. Brull, P. Charrier and L. Mieussens Source Type: research
A nonlinear flow-transition criterion for the onset of slugging in horizontal channels and pipes
In this work, the interfacialinstability and transition of a two-fluidflow from a stratified state to large amplitudewaves or slugs is considered. By combining an asymptotic approximation of the linear Orr-Sommerfeld analysis with nonlinear resonantwave interaction theory, a novel nonlinear slug-transition criterion is derived. This criterion corresponds to a bounding condition on the upper fluid ’s velocity in order to limit the amount ofenergy (provided by the linearinstability) which is transferred to longwaves through resonantwave interactions. It is proposed that such a condition can predict the formation of large-a...
Source: Physics of Fluids - August 4, 2016 Category: Physics Authors: Bryce K. Campbell and Yuming Liu Source Type: research
Flow restrictive and shear reducing effect of magnetization relaxation in ferrofluid cavity flow
In this study, we report theeffects of a uniform stationarymagnetic field on theflow of ferrofluid (FF) inside a boundary driven cavity. A coupled set of conservationequations for theflow field, theMaxwell ’s magnetostaticequations, and the constitutive magnetizationequation are solved numerically. The non-dimensional groups primarily influencing the phenomenon are first systematically identified through the normalization of the complete set ofequations. We find the magnetization relaxationeffects, under the stationary uniform field, to beflow restrictive in nature. The misalignment between the localmagnetic field and th...
Source: Physics of Fluids - August 4, 2016 Category: Physics Authors: Chamkor Singh, Arup Kumar Das and Prasanta Kumar Das Source Type: research
Erratum: “Stretch and hold: The dynamics of a filament governed by a viscoelastic constitutive model with thixotropic yield stress behavior” [Phys. Fluids 28(5) 053104 (2016)]
(Source: Physics of Fluids)
Source: Physics of Fluids - August 4, 2016 Category: Physics Authors: Y. Renardy and H. V. Grant Source Type: research
High-order exact solutions for pseudo-plane ideal flows
A steady pseudo-plane idealflow (PIF)model is derived from the 3D Eulerequations under Boussinesq approximation. Themodel is solved analytically to yield high-degreepolynomialexact solutions. Unlike quadraticflows, the cubic and quartic solutions display reduced geometry in the form of straightlinejet, circularvortex, and multipolar strain field. The high-order circular-vortex solutions are vertically aligned and even the non-aligned multipolar strain-field solutions display vertical concentricity. Such geometry reduction is explained by an analytical theorem stating that only straightlinejet and circularvortex have functi...
Source: Physics of Fluids - August 3, 2016 Category: Physics Authors: Che Sun Source Type: research
A transport equation for reaction rate in turbulent flows
Newtransport equations for chemical reaction rate and its mean value in turbulent flows have been derived andanalyzed. Local perturbations of the reaction zone by turbulenteddies are shown to play a pivotal role even for weakly turbulent flows. The mean-reaction-ratetransport equation is shown to involve two unclosed dominant terms and a joint closure relation for the sum of these two terms is developed. Obtained analytical results and, in particular, the closure relation are supported by processing two widely recognized sets of data obtained from earlier direct numerical simulations of statistically planar 1D premixedflam...
Source: Physics of Fluids - August 3, 2016 Category: Physics Authors: V. A. Sabelnikov, A. N. Lipatnikov, N. Chakraborty, S. Nishiki and T. Hasegawa Source Type: research
Thermal-solutal capillary-buoyancy flow of a low Prandtl number binary mixture with a −1 capillary ratio in an annular pool
A series of three-dimensional numerical simulations on thermal-solutal capillary-buoyancyflow in an annular pool were carried out. The pool was filled with silicon-germanium melt with an initial silicon mass fraction of 1.99%. The Prandtl number and the Lewis number of the working fluid are 6.37 × 10−3 and 2197.8, respectively. Both the radial temperature gradient and the solute concentration gradient were applied to the annular pool. The capillary ratio was assumed to be −1, which means that the solutal and thermal capillary effects were equal and opposite. Results show that the thermal-solutal capillary-buoyancyflow...
Source: Physics of Fluids - August 2, 2016 Category: Physics Authors: Jia-Jia Yu, Chun-Mei Wu, You-Rong Li and Jie-Chao Chen Source Type: research
Instability of Pollard ’s exact solution for geophysical ocean flows
In this paper we apply the short-wavelengthperturbation method to deriveinstability criteria for the three-dimensionalnonlinear Pollardgeophysicalwaves. We show that thesewaves are linearly unstable when thewave steepness exceeds a certain threshold. (Source: Physics of Fluids)
Source: Physics of Fluids - August 2, 2016 Category: Physics Authors: Delia Ionescu-Kruse Source Type: research
Stability of stratified two-phase flows in inclined channels
Linear stability of the stratifiedgas-liquid and liquid-liquid plane-parallelflows in the inclined channels is studied with respect to all wavenumberperturbations. The main objective is to predict the parameter regions in which the stable stratified configuration in inclined channels exists. Up to three distinct base states with different holdups exist in the inclinedflows, so that the stability analysis has to be carried out for each branch separately. Special attention is paid to the multiplesolution regions to reveal the feasibility of the non-unique stable stratified configurations in inclined channels. The stability b...
Source: Physics of Fluids - August 2, 2016 Category: Physics Authors: I. Barmak, A. Yu. Gelfgat, A. Ullmann and N. Brauner Source Type: research
Bubbling behaviors induced by gas-liquid mixture permeating through a porous medium
This paper investigates the bubbling behaviors induced bygas-liquid mixture permeating throughporous medium (PM), which was observed in developing immersion lithography system and was found having great differences with traditional bubbling behaviors injected with only gas phase through the PM. An experimental setup was built up to investigate the bubbling characteristics affected by the mixedliquid phase. Both theflow regimes ofgas-liquid mixture in micro-channel (upstream of the PM) and the bubblingflow regimes inwater tank (downstream of the PM) were recorded synchronously by high-speed camera. The transitions between t...
Source: Physics of Fluids - August 2, 2016 Category: Physics Authors: Liang Hu, Mingbo Li, Wenyu Chen, Haibo Xie and Xin Fu Source Type: research
High fidelity simulation and analysis of liquid jet atomization in a gaseous crossflow at intermediate Weber numbers
Recent advances in numerical methods coupled with the substantial enhancements in computing power and the advent of high performance computing have presented first principle, high fidelity simulation as a viable tool in the prediction and analysis of spray atomization processes. The credibility and potential impact of such simulations, however, has been hampered by the relative absence of detailed validation against experimental evidence. The numerical stability and accuracy challenges arising from the need to simulate the highliquid-gas density ratio across the sharpinterfaces encountered in theseflows are key reasons for...
Source: Physics of Fluids - August 2, 2016 Category: Physics Authors: Xiaoyi Li and Marios C. Soteriou Source Type: research
Bifurcation analysis of the behavior of partially wetting liquids on a rotating cylinder
We discuss the behavior of partiallywettingliquids on a rotating cylinder using a model that takes into account the effects of gravity, viscosity, rotation,surface tension, and wettability. Such a system can be considered as a prototype for many other systems where the interplay of spatial heterogeneity and a lateral driving force in the proximity of a first- or second-order phase transition results in intricate behavior. So does a partiallywettingdrop on a rotating cylinder undergo a depinning transition as the rotation speed is increased, whereas for ideallywettingliquids, the behavior only changes quantitatively. We ana...
Source: Physics of Fluids - August 2, 2016 Category: Physics Authors: Te-Sheng Lin, Steven Rogers, Dmitri Tseluiko and Uwe Thiele Source Type: research
Publisher ’s Note: “Parametric experimental studies on mixing characteristics within a low area ratio rectangular supersonic gaseous ejector” [Phys. Fluids 28, 076101 (2016)]
(Source: Physics of Fluids)
Source: Physics of Fluids - August 2, 2016 Category: Physics Authors: S. K. Karthick, Srisha M. V. Rao, G. Jagadeesh and K. P. J. Reddy Source Type: research
Variational method for liquids moving on a substrate
A newvariational method is proposed to calculate the evolution ofliquid film andliquiddroplet moving on a solid substrate. A simple time evolutionequation is obtained for the contact angle of aliquid film that starts to move on a horizontal substrate. Theequation indicates the dynamical transition at the receding side and the ridge formation at the advancing side. The same method is applied for the evolution of adroplet that starts to move on an inclined solid surface, and again the characteristic shape change of thedroplet is obtained by solving a simple ordinary differential system. We will show that this method has a po...
Source: Physics of Fluids - August 1, 2016 Category: Physics Authors: Xianmin Xu, Yana Di and Masao Doi Source Type: research
