A numerical approach for the direct computation of flows including fluid-solid interaction: Modeling contact angle, film rupture, and dewetting
In this paper, we present a computationally efficient method for including fluid-solid interactions into direct numerical simulations of the Navier–Stokes equations. This method is found to be as powerful as our earlier formulation [K. Mahady et al., “A volume of fluid method for simulating fluid/fluid interfaces in contact with solid boundaries,” J. Comput. Phys. 294, 243 (2015)], while outperforming the earlier method in terms of computational efficiency. The performance and efficacy of the presented method are demonstrated by computing contact angles of droplets at equilibrium. Furthermore, we study the instabilit...
Source: Physics of Fluids - June 1, 2016 Category: Physics Authors: K. Mahady, S. Afkhami and L. Kondic Source Type: research
Velocity fluctuations and population distribution in clusters of settling particles at low Reynolds number
A study on the spatial organization and velocity
fluctuations of non-Brownian spherical particles settling at low Reynolds number in a vertical Hele-Shaw cell is reported. The particle volume fraction ranged from 0.005 to 0.05, while the distance between cell plates ranged from 5 to 15 times the particle radius. Particle tracking revealed that particles were not uniformly distributed in space but assembled in transient settling clusters. The population distribution of these clusters followed an exponential law. The measured
velocity
fluctuations are in agreement with that pre...
Source: Physics of Fluids - June 1, 2016 Category: Physics Authors: A. Boschan, B. L. Ocampo, M. Annichini and G. Gauthier Source Type: research
A direct numerical simulation study on the possibility of macroscopic turbulence in porous media: Effects of different solid matrix geometries, solid boundaries, and two porosity scales
In this study, we address the question of whether turbulent structures in a porous medium are restricted in size by the pore scale or whether the size of eddies may exceed the pore scale, leading to the formation of macroscopic coherent structures. Based on direct numerical simulations in porous media, we conclude that the size of turbulent eddies is restricted by the pore size, leading to the pore scale prevalence hypothesis (PSPH). We prove this hypothesis by considering four different porous matrices. In particular, we simulated turbulent flow in a two-dimensional matrix, a three-dimensional unbounded matrix, a three-di...
Source: Physics of Fluids - June 1, 2016 Category: Physics Authors: M.-F. Uth, Y. Jin, A. V. Kuznetsov and H. Herwig Source Type: research
Droplet migration in a Hele–Shaw cell: Effect of the lubrication film on the droplet dynamics
Droplet migration in a Hele–Shaw cell is a fundamental multiphase flow problem which is crucial for many microfluidics applications. We focus on the regime at low capillary number and three-dimensional direct numerical simulations are performed to investigate the problem. In order to reduce the computational cost, an adaptive mesh is employed and high mesh resolution is only used near the interface. Parametric studies are performed on the droplet horizontal radius and the capillary number. For droplets with an horizontal radius larger than half the channel height, the droplet overfills the channel and exhibits a pancake ...
Source: Physics of Fluids - June 1, 2016 Category: Physics Authors: Yue Ling, Jose-Maria Fullana, Stéphane Popinet and Christophe Josserand Source Type: research
Scaling law for bubbles rising near vertical walls
This paper examines the rising motion of a layer of gas bubbles next to a vertical wall in a liquid in the presence of an upward flow parallel to the wall to help with the understanding of the fluid dynamics in a bubbly upflow in vertical channels. Only the region near the wall is simulated with an average pressure gradient applied to the domain that balances the weight of the liquid phase. The upward flow is created by the rising motion of the bubbles. The bubbles are kept near the wall by the lateral lift force acting on them as a result of rising in the shear layer near the wall. The rise velocity of the bubbles sliding...
Source: Physics of Fluids - June 1, 2016 Category: Physics Authors: Sadegh Dabiri and Pramod Bhuvankar Source Type: research
Large eddy simulations of a transcritical round jet submitted to transverse acoustic modulation
This study specifically focuses on the interaction of the jet with the acoustic field to investigate how the round transcritical jet changes its shape and mixes with the surrounding fluid. Different modulation amplitudes and frequencies are used to sweep a range of conditions. When the acoustic field is established in the domain, the jet length is notably reduced and the jet is flattened in the spanwise direction. Two regimes of oscillation are identified: for low Strouhal numbers a large amplitude motion is observed, while for higher Strouhal numbers the jet oscillates with a small amplitude around the injector axis. The ...
Source: Physics of Fluids - May 31, 2016 Category: Physics Authors: M. Gonzalez-Flesca, T. Schmitt, S. Ducruix and S. Candel Source Type: research
The effect of Prandtl number on mixing in low Reynolds number Kelvin-Helmholtz billows
The effect of Prandtl number on mixing in temporally evolving Kelvin-Helmholtz (KH)
instabilities at low to moderate Reynolds numbers is studied through direct numerical simulation. We distinguish between the mixing induced by the primary billow and the mixing generated by three-dimensional motions by performing each simulation in two and three dimensions. The results indicate that the time evolution of the rate of two- and three-dimensional mixing through different stages of the life cycle of KH
flow is significantly influenced by the Prandtl number. As the Prandtl number increases, the fin...
Source: Physics of Fluids - May 31, 2016 Category: Physics Authors: M. Rahmani, B. R. Seymour and G. A. Lawrence Source Type: research
Numerical study of two-dimensional flow around two side-by-side circular cylinders at low Reynolds numbers
Incompressible flows at low Reynolds numbers over two identical side-by-side circular cylinders have been investigated numerically using unstructured finite volume method. The gap between the cylinders (g) and Reynolds number (Re) considered in the study lies respectively in the range of 0.2 ≤ g/D ≤ 4.0 (D being the diameter of the cylinder) and 20 ≤ Re ≤ 160. Low Reynolds number steady flows are given considerable importance. Two types of wakes are observed in the steady flow regime; the first type is characterized by attached vortices as in the case of an isolated cylinder and the other type is identified by deta...
Source: Physics of Fluids - May 27, 2016 Category: Physics Authors: Sintu Singha, Kaushik Kumar Nagarajan and K. P. Sinhamahapatra Source Type: research
Limiting tensile strength of liquid nitrogen
The method of pulsed liquid superheating in a tension wave that forms when a compression pulse is reflected from the liquid free surface has been used to investigate the kinetics of spontaneous cavitation in liquid nitrogen. The limiting tensile stress pn of nitrogen corresponding to nucleation rates J = 1020 − 1022 s−1 m−3 and the slope of the temperature dependence of the nucleation rate GT = dlnJ/dT have been determined by experiment. The results of experiments are compared with classical nucleation theory (CNT) and a modified classical nucleation theory (MCNT), which takes into account the size dependence of the ...
Source: Physics of Fluids - May 26, 2016 Category: Physics Authors: Vladimir G. Baidakov, Vladimir E. Vinogradov and Pavel A. Pavlov Source Type: research
Turbulent boundary layers along straight and curved long thin circular cylinders at low angles-of-incidence
Long thin circular cylinders commonly serve as towed sonar tracking devices, where the radius-of-curvature along the longitudinal axis is quite low [ρr = O(10−4)]. Because no understanding presently exists about the direct impact of longitudinal curvature on the turbulent statistics, the long cylinder is simply viewed as a chain of straight segments at various (increasing then decreasing) small inclinations to the freestream direction. Realistically, even our statistical evidence along straight thin cylinders at low incidence angles is inadequate to build solid evidence towards forming reliable empirical models. In the ...
Source: Physics of Fluids - May 26, 2016 Category: Physics Authors: Stephen A. Jordan Source Type: research
Simulation of bubble expansion and collapse in the vicinity of a free surface
The present paper focuses on the numerical simulation of the interaction of laser-generated bubbles with a free surface, including comparison of the results with instances from high-speed videos of the experiment. The Volume Of Fluid method was employed for tracking liquid and gas phases while compressibility effects were introduced with appropriate equations of state for each phase. Initial conditions of the bubble
pressure were estimated through the traditional Rayleigh Plesset equation. The simulated bubble expands in a non-spherically symmetric way due to the interference of the free surface, obtaining ...
Source: Physics of Fluids - May 25, 2016 Category: Physics Authors: P. Koukouvinis, M. Gavaises, O. Supponen and M. Farhat Source Type: research
Self-diffusiophoretic colloidal propulsion near a solid boundary
Self-propelled, chemically powered colloidal locomotors are swimmers designed to transverse small scale landscapes in a range of applications involving micropumping, sensing, and cargo transport. Although applications can require precise navigation and onboard steering mechanisms, here we examine by calculation how locomotors through their hydrodynamic interaction can navigate along a boundary. We adopt an engine model consisting of a spherical Janus colloid coated with a symmetrical catalyst cap, which converts fuel into a product solute. The solute is repelled from the colloid through a repulsive interaction, which occur...
Source: Physics of Fluids - May 25, 2016 Category: Physics Authors: Ali Mozaffari, Nima Sharifi-Mood, Joel Koplik and Charles Maldarelli Source Type: research
Multi-dimensional rheology-based two-phase model for sediment transport and applications to sheet flow and pipeline scour
Sediment transport is fundamentally a two-phase phenomenon involving fluid and sediments; however, many existing numerical models are one-phase approaches, which are unable to capture the complex fluid-particle and inter-particle interactions. In the last decade, two-phase models have gained traction; however, there are still many limitations in these models. For example, several existing two-phase models are confined to one-dimensional problems; in addition, the existing two-dimensional models simulate only the region outside the sand bed. This paper develops a new three-dimensional two-phase model for simulating sediment...
Source: Physics of Fluids - May 24, 2016 Category: Physics Authors: Cheng-Hsien Lee, Ying Min Low and Yee-Meng Chiew Source Type: research
Mass transport by mode-2 internal solitary-like waves
We present the first three-dimensional numerical simulations of the mass transport capabilities of mode-2 waves formed by a lock-release mechanism with both single and double pycnocline stratifications. Single pycnoclines and double pycnoclines with a small spacing between the pycnocline centres were found to exhibit large Lee instabilities which formed during the collapse of the intermediate density region. These instabilities led to the generation of vorticity dipoles across the mid-depth, and thereby contributed to the reduction in the mass transported by the wave. A double pycnocline with a separation of approximately ...
Source: Physics of Fluids - May 24, 2016 Category: Physics Authors: David Deepwell and Marek Stastna Source Type: research
Analytical and numerical analysis of bifurcations in thermal convection
of viscoelastic fluids saturating a porous square box
We report theoretical and numerical results on bifurcations in thermal
instability for a viscoelastic fluid saturating a porous square cavity
heated from below. The modified Darcy law based on the Oldroyd-B model was used for
modeling the momentum equation. In addition to Rayleigh number ℜ, two more
dimensionless parameters are introduced, namely, the relaxation time
λ
1 and the retardation time λ
2. Temporal stability analysis showed
that the first bifurcation from the conductive state may be eith...
Source: Physics of Fluids - May 23, 2016 Category: Physics Authors: A. Taleb, H. BenHamed, M. N. Ouarzazi and H. Beji Source Type: research
