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 G5: CFD III: Multiphase Flow |
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Chair: Yves Dubief, University of Vermont Room: 308 |
Monday, November 21, 2011 8:00AM - 8:13AM |
G5.00001: The Immersed Interface Method for Two-Fluid Problems Miguel Uh, Sheng Xu Many problems of fluid mechanics involve the interaction of two immisible fluids. It is generally difficult and inefficient to simulate each fluid separately using an interface-fitted grid method. In the immersed interfaced method a two fluid problem is formulated as one set of governing equations and simulated on a fixed Cartesian grid. The effect of the two-fluid interface enters the formulation as a singular force and a numerical scheme as jump conditions. In these talk we will present the principal jump conditions, discuss the difficulties in implementing them and provide a few options to overcome the difficulties. Finally we will demonstrate the accuracy and efficiency of our immersed interface method for two fluid flow simulations. [Preview Abstract] |
Monday, November 21, 2011 8:13AM - 8:26AM |
G5.00002: Using particles to improve gradient-augmented level set methods for surface advection Olivier Mercier, J.-C. Nave, R.R. Rosales, B. Seibold Level set methods use the zero contour of an implicit function to represent a surface. Traditional methods only track values of the level set function on grid points at each time step. Gradient-augmented methods (and more generally jet-schemes) also keep track and use derivative information. In this talk we will show how these gradient-augmented methods offer a natural framework for incorporating Lagrangian particle information to improve the conservation of mass during advection of surfaces. [Preview Abstract] |
Monday, November 21, 2011 8:26AM - 8:39AM |
G5.00003: The Augmented Fast Marching Method for Level Set Reinitialization David Salac The modeling of multiphase fluid flows typically requires accurate descriptions of the interface and curvature of the interface. Here a new reinitialization technique based on the fast marching method for gradient-augmented level sets is presented. The method is explained and results in both 2D and 3D are presented. Overall the method is more accurate than reinitialization methods based on similar stencils and the resulting curvature fields are much smoother. The method will also be demonstrated in a sample application investigating the dynamic behavior of vesicles in general fluid flows. [Preview Abstract] |
Monday, November 21, 2011 8:39AM - 8:52AM |
G5.00004: High-order jet-schemes for problems with moving interfaces Jean-Christophe Nave, Benjamin Seibold, Ruben Rosales Gradient-augmented and more generally jet-schemes belong to a new class of optimally-local and high order methods. In this talk I will present their general formalism and show several applications to level set interface tracking problems. Also, I will try to highlight the ubiquity of the approach and the simplicity of implementation. [Preview Abstract] |
Monday, November 21, 2011 8:52AM - 9:05AM |
G5.00005: Computation of droplet interactions in a turbulent flow Claudio Torres, Louis Rossi To simulate tropical mesoscale clouds, we compute flows induced by interacting droplets in a turbulent background flow. The calculation of interactions between droplets, modeled as Stokeslets, is the most computationally expensive component in the full cloud simulation. In practice, we have found GMRes to be a superior algorithm for solving this system relative to block-Jacobi and similar schemes, and we report on our attempt to analyze the suitability of this algorithm in general circumstances. Our stability study reveals that a disperse cloud of droplets GMRes will converge robustly. However, when a large number of droplets ($\sim$40) cluster, the condition number grows and GMRes may stagnate. This change in behavior is related to the distribution of the eigenvalues of the matrix. For a uniform disperse set of droplets, we found that the eigenvalues can be enclosed by an ellipse around 1, with some eigenvalues having a small imaginary part. However, for a clustered set of droplets some eigenvalues start to approach zero, indicative of poor GMRes performance. Finally, we will report on our attempts to develop an effective preconditioner to accelerate these calculations on peta-scale computing machines. [Preview Abstract] |
Monday, November 21, 2011 9:05AM - 9:18AM |
G5.00006: Net Flow in Oscillating Drops activated by Time-periodic Wettability Change Jung Min Oh, Dominique Legendre, Frieder Mugele We use numerical (volume of fluid) simulations to study the net flow in sessile drops driven to oscillate at variable frequency by time-periodic variations of the wettability. Superimposed onto an oscillatory component, we find a net flow oriented upward along the surface from the contact line towards the apex and downward along the symmetry axis of the drop. Analyzing the trajectories of Lagrangian tracer particles, we find that the velocity of the mean flow vanishes at high and low drive frequencies with a broad maximum in between in agreement with recent experimental observations [Mugele et al. Lab Chip 2011]. Superimposed onto this general trend sharp maxima appear at frequencies corresponding to even shape modes of the drops, with an absolute maximum at the resonance frequency of the $P_6$ mode. The overall trend follows the behavior expected from a Stokes drift model. [Preview Abstract] |
Monday, November 21, 2011 9:18AM - 9:31AM |
G5.00007: Sharp Interface LES of Breaking Waves in Orthogonal Curvilinear Coordinates Zhaoyuan Wang, Jungsoo Suh, Jianming Yang, Frederick Stern A sharp interface large-eddy simulation (LES) methodology in orthogonal curvilinear coordinates for the breaking waves produced by a body at high Reynolds number is presented. Both gas and liquid phases are considered for the strong interactions between two phases, such as spray dispersion and bubble entrainment. The level-set based ghost fluid method is adopted for sharp interface treatment and a volume-of-fluid method in orthogonal curvilinear coordinates is coupled with the level set method for enhanced interface tracking properties. A Lagrangian dynamic Smagorinsky subgrid-scale model is used for the spatially filtered turbulence closure. Several small-scale cases, bubbles and droplets, are calculated and compared with reference data to validate the sharp interface method on orthogonal curvilinear grids. Wave breaking over a submerged bump and around a wedge-shaped bow is simulated to demonstrate the capabilities of the solver. [Preview Abstract] |
Monday, November 21, 2011 9:31AM - 9:44AM |
G5.00008: An iterative two-fluid pressure solver based on the immersed interface method Sheng Xu An iterative solver based on the immersed interface method is proposed to solve the pressure in a two-fluid flow on a Cartesian grid with second-order accuracy in the infinity norm. The iteration is constructed by introducing an unsteady term in the pressure Poisson equation. In each iteration step, a Helmholtz equation is solved on the Cartesian grid using FFT. The combination of the iteration and the immersed interface method enables the solver to handle various jump conditions across a two-fluid interface. This solver can also be used to solve Poisson equations on irregular domains. [Preview Abstract] |
Monday, November 21, 2011 9:44AM - 9:57AM |
G5.00009: Direct Numerical Simulation of Density Currents over Rough Walls Kiran Bhaganagar, Xiaofeng Liu Direct numerical simulation solver has been developed to simulate density currents over rough walls. The Navier Stokes equations are solved using 4$^{th}$ order vertical velocity equation and a 2$^{nd}$ order vertical vorticity equation. The roughness is introduced using an elegant immersed boundary method (IBM). Spatial discretization is performed using a high order compact finite differences scheme. The time integration is performed using semi-implicit scheme consisting of an explicit 4$^{th}$ order low-storage Runge Kutta scheme for the nonlinear terms and a Crank-Nicolson scheme for the viscous terms. In this talk we will present the fundamental differences in the entrainment due to the presence of 2D and 3D roughness, and we will present an approach to characterize entrainment in terms of the roughness number and Grashoff's number. [Preview Abstract] |
Monday, November 21, 2011 9:57AM - 10:10AM |
G5.00010: The Interaction Between Non-Equilibrium Turbulence and a Thermally Ablative Surface Ryan Crocker, Yves Dubief This main interest of this work concerns the interplay between an erosive flow and erodible surface when the erosive process is low enthalpy ablation. Such systems are know to create coherent ablation patters and cascading mass loss rates due the dynamic interactions between the changing topography of the surface and the near wall physics of turbulent flow. These interactions demonstrate a strong coupling between the mass, momentum, and heat transfers in both time and space. In an attempt to elucidate these couplings and their interconnection a direct numerical algorithm has been developed to simulate ablative turbulent flows. The large jump in physical parameters across the interface is handled with the ghost fluid technique and the surface is tracked with level set methods advected and reinitialized with a fully conservative fast marching method. A mass conserving, cut cell, immersed boundary method is employed to simulate the interaction between the momentum equations and the ablating boundary on a non-conforming mesh. Known solutions to conjugate heat transfer, melting and solidification (both Stefan and Neumann) are used to validate the procedure. [Preview Abstract] |
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