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 LL: CFD IV: Multiphase Flows |
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Chair: Jean-Christophe Nave, Massachusetts Institute of Technology Room: 200A |
Monday, November 23, 2009 3:35PM - 3:48PM |
LL.00001: Gradient-Augmented Level Set and Sub-Grid Accuracy in Multi-Phase Simulations Jean-Christophe Nave In this presentation we will discuss a new method for solving the advection equation for a level set function. The approach relies on carrying both function values and gradients of the level set function as coupled evolved quantities, using Hermite interpolants and a semi-Lagrangian strategy. Some benefits compared to the traditional WENO approach include: better mass conservation, no need to solve a reinitialization equation, ability to capture features smaller than the grid resolution, computational speed, optimally local stencils, and second order accurate curvature calculation. To demonstrate the value of the new method, we will present several two-phase flow simulations for which sub-grid accuracy is important. [Preview Abstract] |
Monday, November 23, 2009 3:48PM - 4:01PM |
LL.00002: A finite element method for simulating thermally fluctuating Brownian particles: Random force vs Random stress Uma Balakrishnan, T.N. Swaminathan, R. Radhakrishnan, D.M. Eckmann, P.S. Ayyaswamy Targeted nanocarrier drug delivery holds promise for personalized medicine, but its optimization requires an accurate description of carrier motion. Our computational approach is aimed at situations where both Brownian motion and the hydrodynamic interactions are important. We consider two ways of assessing this motion: (a) time-correlated random forces (colored noise) acting on the particles, (b) hydrodynamic random stresses in the fluid equations (white noise). The first approach is geometry dependent, the number of random numbers (R$_n$) generated per step is equal to the number of particles. However, the second approach is geometry independent and requires R$_n$ to be equal to the number of mesh points. Both the approaches have been investigated and the results are validated by comparing the calculated temperature of the system, with that determined from the equipartition theorem, and by comparing the predicted mean square displacement with that calculated from Einstein's formula. While both approaches yield comparable accuracies, the random stress approach appears to be more robust and readily generalizable to complex particle as well as flow geometries. [Preview Abstract] |
Monday, November 23, 2009 4:01PM - 4:14PM |
LL.00003: ABSTRACT WITHDRAWN |
Monday, November 23, 2009 4:14PM - 4:27PM |
LL.00004: Computational Fluid Dynamics Study of the Effect of Turbulence and Two-Phase Flow on Flow Blurring Atomization Jorge Ramon, Willard Schreiber A novel atomization mechanism known as Flow Blurring (FB) mixes air with liquid to produce a fine spray. While the geometry of Flow Blurring is simple, the fluid mechanics of the two-phase mixing is complicated. CFD modeling of the Flow Blurring injector has been attempted previously assuming laminar one phase mixing between two different density gases. The objective of the present work was to study the effect of adding turbulence and two-phase flow to the previous CFD model. The k-$\varepsilon$, k-$\omega $, and Reynolds stress models were investigated for representing turbulence. The k-$\varepsilon $ realizable model produces the best results both from the standpoint of physical realism and numerical convergence and allows the Reynolds number based on flow characteristics of the FB injector to be increased by a factor of six. Three models of two-phase flow were examined: Volume of Fluid, Mixture, and Eulerian, none of which satisfactorily simulated two-phase mixing in the FB atomizer. [Preview Abstract] |
Monday, November 23, 2009 4:27PM - 4:40PM |
LL.00005: Steady/Unsteady Solutions of Full 2-D Governing Equations of Internal Condensing Flows, Their Responses to Flow Disturbances, and Their Controllability through Exit Conditions Shantanu Kulkarni, Amitabh Narain, Soumya Mitra This paper presents novel computational results obtained for the full 2-D governing equations of condensing flows in a channel (shear driven or gravity driven). It is shown that the internal condensing flows can be operated under two different boundary conditions at the exit, viz. unspecified exit condition and specified exit condition. These computational results state that for unspecified exit conditions, there exists a unique steady solution for the condensing flows, termed as ``natural'' solution. This ``natural'' solution is obtained by solving ``strictly'' steady governing equations. This paper demonstrates that the unsteady equations of condensing flows are \textit{elliptic} and for the specified exit conditions different than the ``natural'' exit condition, one obtains an unsteady or quasi-steady solution based on the type of exit condition control. This paper demonstrates different ways to control the exit condition as well as solution attainability limits for gravity and shear driven flows. [Preview Abstract] |
Monday, November 23, 2009 4:40PM - 4:53PM |
LL.00006: An Eulerian Numerical Method for Fluid-Solid Interaction Yang Zhang, Ken Kamrin, Jean-Christophe Nave Fluid-solid interaction is a difficult computational problem, primarily because solids and fluids are described in different perspectives --- solid laws are written in Lagrangian frame while fluids are represented in Eulerian. Our work attempts to resolve this dilemma using a new method for Eulerian solid mechanics. We study the interaction of a large-deformation elastic solid with a Newtonian fluid in a single computational framework. We use a level set to track the interface between the two phases. The standard projection method is used to impose incompressibility in both phases, and the equations are discretized with an explicit, staggered finite-difference scheme. In the current implementation, a smeared Heaviside function is used to blur material properties across the interface. Simulations of various test cases will be presented in this talk. [Preview Abstract] |
Monday, November 23, 2009 4:53PM - 5:06PM |
LL.00007: Efficient Simulation of Fully Coupled Wave-Body Interactions on a Cartesian Grid Jianming Yang, Frederick Stern The sharp interface Cartesian grid method by Yang and Stern (Sharp interface immersed-boundary/level-set method for wave-body interactions, J. Comput. Phys. 228 (2009) 6590-6616) is extended for the efficient simulation of fully coupled wave-body interactions of a single body with a two-phase incompressible flow. The overall approach is based on a fractional-step method using finite differencing on a staggered Cartesian grid and the governing equations are solved in a non-inertial reference frame following the motion of the body. A level set method is adopted for the fluid-fluid interface tracking and a direct forcing immersed boundary method is used for the fluid-solid boundary treatment. The relationship between the body velocity and the explicit momentum forcing given by Kim and Choi (Immersed boundary method for flow around an arbitrarily moving body, J. Comput. Phys. 212 (2006) 662-680) is utilized for the non-iterative solution of fluid-structure interactions. The forces and moments calculation in the framework of solid-liquid-gas system is emphasized. Several cases ranging from water entry problems to ship moving in waves are demonstrated to showcase the accuracy and efficiency of the method. [Preview Abstract] |
Monday, November 23, 2009 5:06PM - 5:19PM |
LL.00008: Numerical simulation of the formation of liquid bridge with movable contact line by an external electric field Jin Seok Hong, In Seok Kang The authors have suggested a new dispensing method of droplets on demand, which is a counter-electrode-free electrohydrodynamic method with no pump and an inverted geometry; a top substrate and a bottom nozzle. Using this method, the authors have also demonstrated highly uniform dispensing results with a variance 1.8 {\%} in droplet diameter. The dispensing process consists of two stages of liquid bridge (LB) formation by an applied electric pulse and its break-up by the movement of top plate. In this work, numerical simulation is performed for the first LB formation stage. The dynamics of liquid surface during LB formation is analyzed numerically for a simple liquid such as water. Especially, the movement of upper contact line is studied with respect to the dynamic contact angle model for the top plate. In addition, the asymmetry of the contact line mobility between nozzle and the top plate is also considered and its effect on the final upper contact area is analyzed. The numerical results are compared with the experimental results and discussed in terms of the effect of applied electric pulse. [Preview Abstract] |
Monday, November 23, 2009 5:19PM - 5:32PM |
LL.00009: Numerical simulation of the flow patterns within concentric spheres with rotation and solid-liquid phase change Ares Cabello, Ruben Avila We present the flow patterns in the interior of a spherical
annulus at different Taylor (Ta) numbers and for two Stefan (St)
numbers. The equations of the two phases are solved in a
Cartesian coordinate system using a spectral element method, in a
reference frame that is turning with the system, then the
centrifugal and Coriolis terms are considered. Firstly the Stefan
number was equal to zero i.e. without solidification from the
outer boundary. Secondly the St number was fixed to $St=6\times
10^{-3}$, hence the growing of a solid crust from the outer
sphere was allowed. When the Ta number is in the range
$Ta<3\times 10^5$ (subcritical regime), it is observed a basic
flow. A transitional oscillatory stage appears when the Ta number
is increased in the interval ($3\times 10^5 |
Monday, November 23, 2009 5:32PM - 5:45PM |
LL.00010: An Improved Bubble Packing Method for Unstructured Mesh Generation with Applications in Computational Fluid Dynamics Lilong Wu, Bin Chen An improved Bubble Packing Method (BPM) is proposed to generate high-quality unstructured mesh for prediction of the flow dynamics in a domain with complex geometries. For curved-boundary domain, firstly each curved boundary is mapped into a straight line, and then new bubble positions will be mapped into curved boundary back by arc-length parameterization method after the bubble system on the mapped straight line reaches equilibrium. In this way the bubble's departure from curved boundaries during dynamic movement of the bubbles can be avoided. Moreover, the grid density can be controlled simply and effectively. Local mesh refinement is realized by adding different size bubbles to the real / artificial vertices of the domain and bubble information of these vertices is transferred to the inner nodes of the domain by using the Shepard interpolation method. In order to validate the proposed algorithm, unstructured collocated grid systems are developed to numerically simulate lid-driven flow in square and polar cavities. The good agreement between numerical simulations with literatures under different Reynolds numbers confirms the effectiveness and feasibility of our proposed algorithm. [Preview Abstract] |
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