Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session M13: Multiphase Flow VI: Numerical III |
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Chair: Howard Hu, University of Pennsylvania Room: 316 |
Tuesday, November 22, 2011 8:00AM - 8:13AM |
M13.00001: Dynamics of elastic particles in an elongational flow Tong Gao, Howard Hu, Pedro Ponte Castaneda We consider dynamics of elastic particles in a steady elongational viscous flow under Stokes flow conditions. The particle is assumed to be an incompressible neo-Hookean elastic solid. A polarization technique based on Eshelby's problem in elasticity is used to describe the finite-strain, time-dependent response of the particle. Under simple flow conditions (e.g., with constant velocity gradient), a set of coupled, nonlinear, first-order ODEs is obtained for the evolution of the uniform stress fields in the particle, as well as for the shape and orientation of the particle. In the elongational flow, the particle deforms and rotates to align with the flow directions before reaching steady state. However, the steady-state solutions only exist in certain regimes where the deformation is not very large. In 2D, the closed-form analytical solutions can be solved directly; while in 3D, the solutions have to be solved numerically. The results of initially spherical shaped particles compare well with those of the classical work by Roscoe (1967). [Preview Abstract] |
Tuesday, November 22, 2011 8:13AM - 8:26AM |
M13.00002: Dynamics of elastic particles in a shear flow Howard Hu, Tong Gao, Pedro Ponte Castaneda We study the dynamics of elastic particles in a simple shear flow under Stokes flow conditions. Both 2D and 3D situations are considered. The particle is assumed to be an incompressible neo-Hookean elastic solid. A polarization technique based on Eshelby's problem in elasticity is used to describe the finite-strain, time-dependent response of the particle. Under simple flow conditions (e.g., with constant velocity gradient), a set of coupled, nonlinear, first-order ODEs is obtained for the evolution of the uniform stress fields in the particle, as well as for the shape and orientation of the particle. Three types of particle motion which are typically seen in the vesicle motion under shear---steady-state, trembling and tumbling---are captured by changing the shear rate, the elastic modulus and the initial shape. The conditions that determine the trembling- to-tumbling transition, as well as the critical behavior of the particle near transition are explored. Additionally, the effective viscosity of a suspension of such soft particles under shear is also computed. [Preview Abstract] |
Tuesday, November 22, 2011 8:26AM - 8:39AM |
M13.00003: Rotation of triaxial particles in shear and strain: From Jeffery orbits and alignment to oscillations and chaos Fredrik Lundell The rotation of non-spherical particles is a cornerstone for the understanding of particle motion in flows laden with (non-spherical) particles. Here, the rotary motion of triaxial ellipsoids in linear shear and strain is studied theoretically and numerically under the assumption of Stokes flow ($Re=0$). The particle motion is modeled by coupling the torques (Jeffery 1922) with the equations of rotation. The problem is governed by the relationships between the two shorter and the major axis together with the Stokes number, obtained as the Reynolds number times the particle/fluid density ratio. The general behaviour is that the particle ultimately rotates with the shortest axis aligned with the vorticity axis in shear flow. In linear strain, the particle aligns with the strain. However, the route and time to reach this state is distinctively different for different parameter combinations. Furthermore, the ultimate state is unstable for certain parameter combinations and the particle instead moves in a chaotic manner. The results, valid at $Re=0$, shows a wide range of behaviors and provide a firm base for the understanding of particle motion also at higher $Re$. [Preview Abstract] |
Tuesday, November 22, 2011 8:39AM - 8:52AM |
M13.00004: Numerical simulation on subcooled pool boiling bubble behavior Yasuo Ose, Tomoaki Kunugi In this study, it is focused on the clarification of the heat transfer characteristics of the subcooled pool boiling, the discussion on its mechanism, and the establishment of a boiling and condensation model for the direct numerical simulation on the subcooled pool boiling phenomena. In this paper, the boiling and condensation model has been improved by introducing the following models based on the quasi-thermal equilibrium hypothesis: (1) an improved phase-change model which consisted of the enthalpy method for the water-vapor systems, (2) a relaxation time derived by considering the unsteady heat conduction at the vapor-water interface. Then, unsteady three dimensional numerical simulations based on the MARS (Multi-interface Advection and Reconstruction Solver) with the improved boiling and condensation model were performed for the bubble departing process from the heated surface. The results of the numerical simulations were compared with the experimental data obtained by the high-speed camera (Phantom 7.1) with the Cassegrain optical system. As the results, the numerical results of bubble departure behavior from the heated surface showed in good agreement with the experimental observations quantitatively. [Preview Abstract] |
Tuesday, November 22, 2011 8:52AM - 9:05AM |
M13.00005: Lattice Boltzmann Simulation of a Vapor Bubble in a 2D Microchannel Michael Ikeda, Laura Schaefer As energy densities in electronic devices rapidly increase, improved two-phase microchannel heat exchanger designs are of great interest. However, a better understanding of flow boiling in these regimes is needed. Experimental studies have thus far shown a great deal of variety in the flow patterns and instabilities that develop at the microscale level. Thus, numerical techniques capable of simulating such conditions are desirable. To this end, the behavior of a vapor bubble in a 2D microchannel is numerically analyzed. The kinetic lattice Boltzmann method is used over traditional CFD approaches due to its ability to capture the interfacial dynamics of multi-phase flow without the need for interface tracking algorithms. The single- component, multi-phase Shan-Chen model is utilized in conjunction with the passive scalar thermal approach, whereby the temperature field is passively advected by the hydrodynamics of the system. Advanced equations of state are implemented for the reduction of spurious currents and the recovery of realistic temperatures. The bubble dynamics are analyzed with varying Reynolds numbers and thermal boundary conditions. [Preview Abstract] |
Tuesday, November 22, 2011 9:05AM - 9:18AM |
M13.00006: Numerical study on deformation and coalescence of droplets in a two-dimensional channel flow Sungrok Jung, Myounghwan Cho, Hyounggwon Choi, Jungyul Yoo An improved level-set (LS) method is implemented to simulate the two-phase incompressible flow in two-dimensional channel considering the effect of interfacial tension. A mixed element is adopted, so that the Navier-Stokes equations are solved by using the q2q1 integrated finite element method (FEM), and the LS function is solved by using the q1q1 element. Direct approach method using geometric information is implemented instead of the conventional hyperbolic-type partial differential equation for reinitializing the LS function. The present code is verified by comparing the droplet movement and merging process with existing studies. It is shown that the computational results for deformation and migration of the droplets are in good agreement with those of the previous studies. In addition, the droplet merging process in straight and diverging channels is studied by using the present method. Comparing with the experimental data, the results of the present study shows similar tendencies for respective cases. [Preview Abstract] |
Tuesday, November 22, 2011 9:18AM - 9:31AM |
M13.00007: ABSTRACT WITHDRAWN |
Tuesday, November 22, 2011 9:31AM - 9:44AM |
M13.00008: Effects of Surfactant on the Motion of Large Bubbles in a Capillary Tube Metin Muradoglu, Ufuk Olgac The effects of surfactant on the Bretherton problem are studied computationally using both insoluble and soluble surfactant models. Emphasis is placed on the liquid film thickness between the bubble and the tube wall. We solve the evolution equations of the interfacial and bulk surfactant concentrations coupled with the incompressible Navier-Stokes equations. A non-linear equation of state is employed based on Langmuir adsorption. The numerical method is first validated for the clean bubble case and the results are found to be in a good agreement with the semi-analytical Taylor's law. Then the method is used to investigate the effects of insoluble and soluble surfactants on the film thickness for a wide range of governing non-dimensional numbers. It is found that both the insoluble and soluble surfactants have a thickening effect on the liquid film, which compares qualitatively well with both the experimental results and analytical predictions. Further computations are performed to examine the effects of non-dimensional numbers in the insoluble and soluble surfactant cases and it is found that elasticity, Damkohler and Peclet numbers have significant influence on the film thickness. Finally the computations are performed to examine the validity of insoluble surfactant for a wide range of governing nondimensional parameters. [Preview Abstract] |
Tuesday, November 22, 2011 9:44AM - 9:57AM |
M13.00009: Detailed Numerical Simulation of Liquid Jet in Cross Flow Atomization with High Density Ratios Sina Ghods, Marcus Herrmann Atomization of a liquid fluid jet by a high speed cross-flowing gas has many applications such as gas turbines and augmentors. The mechanisms by which the liquid jet initially breaks up, however, are not well understood. Detailed numerical simulation can offer a better understanding of the underlying physical mechanisms that lead to the initial breakup of the injected liquid jet. In this work, we present detailed numerical simulation results of turbulent liquid jets injected into turbulent gaseous cross flows at varying momentum flux ratios and crossflow Weber numbers. We employ a finite volume, balanced force fractional step flow solver to solve the Navier-Stokes equations coupled to a Refined Level Set Grid method to follow the phase interface. To ensure discrete consistency between the solution of the conservative momentum equation and the level set based continuity equation, we employ a novel Rescaled Conservative Momentum Method. We analyze the impact of the previously-mentioned characteristic numbers on jet penetration, atomization mechanism, liquid mass flux distribution, and resulting drop size distribution and compare our numerical results to those obtained experimentally by Brown \& McDonell (2006). [Preview Abstract] |
Tuesday, November 22, 2011 9:57AM - 10:10AM |
M13.00010: A fast Lagrangian tracking method capturing finite-size effects in particulate flows Mingqiu Wu, Julien Favier, Alfredo Pinelli We present a new method to capture the finite-size effects induced by particles transported by a fluid flow, with a low computational cost compared to available fully-resolved methods, thus allowing to tackle configurations with high volume fractions of particles. The basic idea consists in tracking a source/sink of momentum occurring within a compact support of the mesh, centered on the particle and taking the form of a mollified Dirac kernel, or blob. In the spirit of the immersed boundary method, the shape and the intensity of the kernel are found by imposing appropriate reproducing conditions on the blob (to model accurately a Dirac pulse) and spreading on the mesh cells a volume force determined by the desired boundary condition. The particles occupy a finite-size volume of fluid, therefore introducing a two-way coupled behavior, for the computational cost of only one Lagrangian point. To build the blobs, we will either spread a zero-velocity condition at the blob center, or spread a zero-velocity condition averaged on the fluid parcel enclosed within the support. Both methods are discussed and validated by comparing with free falling fully-resolved particles, in 2D and 3D. [Preview Abstract] |
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