Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session GK: Multiphase Flows III |
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Chair: Kyle Squires, Arizona State University Room: 101J |
Monday, November 23, 2009 8:00AM - 8:13AM |
GK.00001: Multiscale modeling of non-homogenous flows with non-Newtonian properties Arturo Fernandez A new multiscale approach to modeling non-homogenous flows where non-Newtonian effects are significant will be discussed. The computations are carried out by combining an immersed-boundary-method, able to capture the response of non-homogenous systems, with Brownian Dynamics able to predict the local properties. The exchange of information between the continuum-based and Brownian Dynamics models, which capture the system properties at different scales, is done through the velocity gradient and stress state tensors. The stress-state tensor estimated with the Brownian Dynamics simulations is introduced in the solution of the front-tracking method, whereas the velocity gradient state is used to estimate the local properties. How to achieve an adequate computational cost will also be discussed. The methodology is validated for two different problems: (i) the deformation of a Newtonian drop immersed in a simple shear flow and suspended in a viscoelastic fluid; (ii) the buoyancy of air bubbles in a viscoelastic fluid. [Preview Abstract] |
Monday, November 23, 2009 8:13AM - 8:26AM |
GK.00002: Single-equation versus multi-equation models in simulation of material flows Xia Ma, Duan Zhang, Paul Giguere, Qisu Zou When considering interactions of two pieces of different materials, often a single momentum equation is used; and different materials are treated as two different species of a solid material. The stress in the momentum equation is calculated differently depending on the material occupying the point. This approach is limited when considering breakup of the materials into pieces with typical size smaller than numerical grid resolution. After the breakup, one would prefer to use a two-equation model to simulate the flow of the debris of the two solid materials. It is a significant issue when and how to switch from single-equation mode to the two-equation model. A different approach is to start with a two-equation model, and to treat the system as continuous two-phase system before the material breakup. When material breakup happens, the equation system has a smooth transition into disperse two-phase flows. The issue is then, how this two-equation approach compared with the single equation approach before the material breakup. What material interaction model is needed for such numerical calculation? The present paper tries to answer some of these questions using numerical examples. [Preview Abstract] |
Monday, November 23, 2009 8:26AM - 8:39AM |
GK.00003: Multiscale Issues in DNS of Multiphase Flows Gretar Tryggvason, Siju Thomas, Jiacai Lu, Bahman Aboulhasanzadeh In spite of the enormous information and understanding that DNS are providing for relatively complex multiphase flows, real systems provide challenges that still limit the range of situations that can be simulated, even when we limit our studies to systems well described by continuum theories. The problem is, as one might expect, one of scale. Starting with simulations where the ``dominant small-scales'' are fully resolved, it is frequently found that multiphase flows also can generate features much smaller than the dominant flow scales, consisting of very thin films, filaments, and drops. Frequently there is a clear separation of scales between these ``features,'' usually inertia effects are relatively small for the local evolution, and in isolation these features are often well described by analytical models. Here we describe the use of a thin film model to account for unresolved features of the flow. By using a semi-analytical model for the flow in the film beneath a drop sliding down a sloping wall, we capture the evolution of films that are too thin to be accurately resolved using a relatively coarse grid that is sufficient to resolve the rest of the flow. Extensions of these ideas to flows with mass and heat transfer as well as phase change and chemical reactions are also discussed. [Preview Abstract] |
Monday, November 23, 2009 8:39AM - 8:52AM |
GK.00004: Smoothed particle hydrodynamics applied to multiphase flows Marion Vance, Kyle Squires Fully Lagrangian numerical simulations of multiphase flows are performed using a numerical approach that is a variation of smoothed particle hydrodynamics. The momentum conservation equation for the constant mass fluid elements is described using the Boltzmann transport equation and particle phase space probability density function. Analogous to the familiar forms of continuum fluid mechanics, the acceleration of a fluid element is due to the gradient of local kinetic stress, the constitutive terms of which are determined following expansion methods from kinetic theory of a dense gas. Including first-order terms, the acceleration of fluid elements is proportional to local particle density and relative velocity, and those elementary forces tend to drive the system towards an equilibrium state. The fundamental restoring and dissipative particle forces are shown to model familiar pressure, viscous, and surface tension effects at the macroscopic scale. The method is applied to test problems that include the wall- bounded flow of two nearly immiscible fluids, the rise of bubbles in an infinite quiescent liquid, and hard sphere sediment transport. Simulations are performed in both two and three dimensions, and the observations are compared to published results. [Preview Abstract] |
Monday, November 23, 2009 8:52AM - 9:05AM |
GK.00005: A Comparison of Multiphase LBGK and MRT LBE Models Yan Peng, Li-Shi Luo One undesirable feature of LBE methods as diffuse interface methods is the existence of parasitic currents. Recently, Lee and Fischer have shown that if the potential form of the intermolecular force is used, the parasitic currents can be eliminated. In their study, the LBGK collision model is used. As we know that multiple-relaxation-time (MRT) collision model has a number of advantages over the lattice Bhatnagar-Gross-Krook (LBGK) model. In this study, we will replace the LBGK with MRT collision model. We compared the stability and Galilean invariance of the two models. The test case is a circular bubble. We found that LBGK is very sensitive to the initial given density values. For the Galilean invariance property, we first get the converged equilibrium solution. Then we add an external velocity. We found that LBGK scheme diverges even a very small velocity is given. From these comparisons, we conclude that MRT is more stable and preserve Galilean invariance better than LBGK. [Preview Abstract] |
Monday, November 23, 2009 9:05AM - 9:18AM |
GK.00006: ABSTRACT WITHDRAWN |
Monday, November 23, 2009 9:18AM - 9:31AM |
GK.00007: Effects of confinement on a rotating sphere Qianlong Liu, Andrea Prosperetti The hydrodynamic force and couple acting on a rotating sphere in a quiescent fluid are modified by nearby boundaries with possible consequences on spin-up and spin-down times of particles uspended in a fluid, their wall deposition, entraiment and others. Up to now, the vast majority of papers dealing with these problems have considered the low-Reynolds-number regime. This paper focuses on the effect of inertia on the hydrodynamic interaction of a spinning sphere with nearby boundaries. Rotation axes parallel and perpendicular to a plane boundary as well as other situations are studied. Several steady and transient numerical results are presented and interptreted in terms of physical scaling arguments. The Navier-Stokes equations for an incompressible, constant-property Newtonian fluid are solved by the finite-difference PHYSALIS method. Among the noteworthy features of this method are the fact that the no-slip condition at the particle surface is satisfied exactly and that the force and torque on the sphere are obtained directly as a by-product of the computation. This feature avoids the need to integrate the stress over the particle surface, which with other methods is a step prone to numerical inaccuracies. A locally refined mesh surrounding the particle is used to enhance the resolution of boundary layers maintaining a manageable overall computational cost. [Preview Abstract] |
Monday, November 23, 2009 9:31AM - 9:44AM |
GK.00008: A linear spatial stability analysis of liquid-gas rotating co-flowing jet Yaohong Wang, Mark Sussman, M.Y. Hussaini We present a linear spatial stability analysis of a liquid-gas rotating co-flowing jet. The parallel mean velocity is computed as a function of the radial coordinate by solving the coupled liquid-gas Navier-Stokes equations in a cylindrical coordinate system. A multi-domain Chebyshev spectral collocation method is applied to the perturbed Navier-Stokes equations (linearized about the mean parallel flow). Both axisymmetric and helical modes are considered. Numerical calculations are performed to obtain the growth rates and frequencies of the most unstable modes. The effect of density ratio, viscosity ratio and surface tension are discussed. [Preview Abstract] |
Monday, November 23, 2009 9:44AM - 9:57AM |
GK.00009: Two Types of Equations for Nonlinear Wave Propagation in a Liquid Containing Microbubbles Tetsuya Kanagawa, Takeru Yano, Masao Watanabe, Shigeo Fujikawa Weakly nonlinear propagation of one-dimensional dispersive waves in mixtures of a liquid and a number of spherical gas bubbles are theoretically investigated based on two-fluid averaged equations derived by the present authors. A set of equations consists of the conservation laws of mass and momentum for gas and liquid phases, and Keller's bubble dynamics equation. The compressibility of liquid leads to the wave attenuation due to bubble oscillations. By using the appropriate scaling of physical parameters and the method of multiple scales, two types of equations for nonlinear wave propagation in long ranges are derived. In a moderately low frequency band, the behavior of weakly nonlinear waves is governed by the KdV-Burgers equation. On the other hand, in a moderately high frequency band, the nonlinear modulation of quasi-monochromatic wave train is governed by the nonlinear Schroedinger equation with an attenuation term. [Preview Abstract] |
Monday, November 23, 2009 9:57AM - 10:10AM |
GK.00010: Fluctuations in number and volume fraction in granular and multiphase flows: implications for theory and modeling Shankar Subramaniam Fluctuations in the number of particles, and consequently the fraction of volume occupied by them, are observed in experiments as well as simulations of granular and multiphase flows. The mathematical representation of these fluctuations is described, and compared with the standard average number density representation in kinetic theory of granular and gas-solid flow. Implications for the strong and weak forms of the conservation laws of hydrodynamic quantities are discussed, and this leads to possible approaches to model the effect of fluctuations. The manifestation of fluctuations in current closure models is examined using data from direct numerical simulation. Implications for the stability analysis of gas-solid flows, and the stability limits calculated from reduced statistical representations are discussed. [Preview Abstract] |
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