Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session EG: CFD II |
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Chair: Miki Amitay, Rensselaer Polytechnic Institute Room: Hilton Chicago Williford A |
Sunday, November 20, 2005 4:10PM - 4:23PM |
EG.00001: Heat transfer in a turbulent channel flow with a blowing/suction velocity boundary condition on the bottom wall Stefano Leonardi, Juan G. Araya, Michael Amitay, Luciano Castillo Direct Numerical Simulations (DNS) of the velocity and thermal fields in a turbulent channel flow with a normal periodic blowing/suction velocity disturbance on the lower wall are presented for high and low Reynolds numbers. The purpose is to reproduce the complex physics of turbulent flows when synthetic jets (zero net mass flux) are placed on the bottom wall in order to enhance heat transfer. In the present paper, synthetic jets are modeled as a time dependant blowing/suction velocity boundary condition with a sinusoidal behavior and the influence of the perturbation frequency on friction and heat transfer coefficients is discussed. [Preview Abstract] |
Sunday, November 20, 2005 4:23PM - 4:36PM |
EG.00002: Generation of Turbulent Inlet Conditions for Thermal Boundary Layer Simulations Juan G. Araya, Elaine Bohr, Kenneth Jansen, Luciano Castillo Realistic environments generally imply spatially evolving turbulent boundary layers, being the flat plate the typical example. In this case, periodic boundary conditions cannot be established in the streamwise direction as in fully developed flows in channels. For this reason, it is necessary to generate turbulent fluctuations at the inlet of the computational domain at every time step. Lund et al. (1998) proposed an ingenious method for accounting spatial growth in the inflow condition based on the similarity of the velocity profiles at different streamwise locations. They extracted a velocity field, from a downstream plane, rescaled it and reintroduced it as a boundary condition at the inlet of the domain. In a posterior study, Kong et al. (2000) extended the previous concept to thermal inflow generation predictions. This research proposes different scales in the inner and outer regions for simulating actual turbulent temperature fluctuations at the entrance of a computational domain based on the Lund's idea: the velocity scales are based on the work of George and Castillo (1997), meanwhile the temperature scaling is derived from investigations performed by Wang and Castillo (2003). Finally, Direct Numerical Simulations of evolving turbulent thermal boundary layers on a flat plate are performed to test the proposed inflow generation model. [Preview Abstract] |
Sunday, November 20, 2005 4:36PM - 4:49PM |
EG.00003: Karhunen-Lo\'{e}ve analysis of coherent structures in viscoelastic turbulent channel flows Geoffrey Oxberry, Robert Handler, Kostas Housiadas, Antony Beris Direct numerical simulation data of viscoelastic turbulent channel flows from Housiadas et al. (Phys. Fluids, 17: 035106, 2005) were analyzed by decomposing the dynamic velocity fields into representative time-invariant eigenfunctions using the Karhunen-Lo\'{e}ve technique. Eigenfunctions were evaluated previously as explained in the aforementioned article. The dominant eigenmodes of flows (ranked by energy) display a structure similar to definitions of turbulent vortices in the literature. Therefore, time-dependent analysis of the velocity field in terms of those eigenfunctions allows one to evaluate the long time behavior of large, coherent structures in the flow. The comparison of the viscoelastic data, obtained with the FENE-P model, against results obtained for Newtonian turbulent channel flow allows for a better understanding of the role of viscoelasticity in turbulence modification leading to drag reduction. [Preview Abstract] |
Sunday, November 20, 2005 4:49PM - 5:02PM |
EG.00004: Dissipative Particle Dynamics Simulations of Colloidal Suspensions Igor Pivkin, George Karniadakis Dissipative Particle Dynamics (DPD) is an off-lattice mesoscopic particle-based simulation method for complex fluids. Due to soft force potential used in DPD, modeling of solid-wall boundary conditions is difficult. We have developed a relatively simple procedure to impose no-slip boundary conditions for DPD. We have applied it to study colloidal suspensions of spherical particles with different volume fractions. We will present simulation results from these studies focusing on the rheological properties and comparisons with experimental results and theoretical predictions. [Preview Abstract] |
Sunday, November 20, 2005 5:02PM - 5:15PM |
EG.00005: An Explicit Finite-Difference Scheme for Particulate Flows with a New Treatment of Boundary Conditions Based on Stokes Flow Solutions Andrew Perrin, Howard Hu We have developed an explicit finite-difference scheme for direct simulation of the motion of solid particles in a fluid. It is challenging to enforce the no-slip condition on the surface of circular particles in a uniform grid. In this study, we have implemented a treatment of the boundary condition similar to that in the PHYSALIS method of Takagi et. al. (2003), which matches Stokes flow solutions next to the particle surface with a numerical solution away from it. The original PHYSALIS method was developed for implicit flow solvers, and required an iterative process to match the Stokes flow solutions with the numerical solution. However, it was easily adapted to work with the present explicit scheme, and found to be more efficient since no iterative process is required in the matching. The method proceeds by approximating the flow next to the particle surface as a Stokes flow in the particle's local coordinates, which is then matched to the numerically computed external flow on a ``cage'' of grid points near the particle surface. Advantages of the method include superior accuracy of the scheme on a relatively coarse grid for intermediate Reynolds numbers, ease of implementation, and elimination of the need to track the particle surface. A disadvantage is that fine grids are required for Reynolds numbers greater than 200. Several examples are presented, including flow over a stationary cylinder, dropping, kissing, and tumbling of two particles, and a dense particulate sedimentation problem. [Preview Abstract] |
Sunday, November 20, 2005 5:15PM - 5:28PM |
EG.00006: Simulation of a Deformable Particle using Lattice Boltzmann Method Sheila Rezak, Robert MacMeccan, Ejiang Ding, Jonathan Clausen, Jingshu Wu, G. Paul Neitzel, Cyrus Aidun The flow characteristic of deformable particles and fibers is largely dependent on the deformation and interaction of the solid phase. For example, in fiber suspension, the transport properties of the suspension and the fiber-fiber interaction and flocculation are dependent on fiber bending stiffness. In blood flow, both viscosity and enhanced mass transport of platelets are dependent on red blood cell membrane stiffness and deformation. A new hybrid method has been developed based on coupling an elastic finite element particle model for particle deformation to the lattice Boltzmann method for fluid transport. The elastic finite element model provides easy incorporation into the lattice Boltzmann framework and enough computational efficiency to allow simulation of suspensions at high volume fractions. Issues related to the new method are discussed in the context of two dimensional deformable spheres and fibers in simple shear flow. In particular, we show deviations from Jeffery's orbit in simple shear flow due to particle deformation and discuss the effect on the flow characteristic. [Preview Abstract] |
Sunday, November 20, 2005 5:28PM - 5:41PM |
EG.00007: Numerical simulation of cocontinuous morphologies Junseok Kim, John Lowengrub, Vittorio Cristini In strongly sheared emulsions, experiments (e.g., Galloway and Macosko 2001) have shown that systems consisting of one continuous (matrix) and one dispersed (drops) phase may undergo a coalescence cascade leading to a system in which both phases are continuous, i.e., cocontinuous, (sponge-like). Such configurations may have desirable diffusional, mechanical and electrical properties and thus have wide-ranging applications. Using a diffuse interface method developed by Kim and Lowengrub 2001, we perform numerical simulations of the interface length per unit area as a function of volume fractions in 2-d. In this approach, interfaces have small but finite thickness and limited chemical diffusion is used to change the topology of interfaces. In this presentation, we discuss the effects of the viscosity ratio, surface tension, and flow on interface length per unit area and compare it with experiment results. The use of adaptive mesh refinement techniques recently developed by Kim, Wise and Lowengrub will also be discussed. [Preview Abstract] |
Sunday, November 20, 2005 5:41PM - 5:54PM |
EG.00008: Introducing CFD in Introductory Undergraduate Fluid Mechanics Courses John M. Cimbala Many instructors want to introduce CFD into their introductory junior-level fluid mechanics course, but cannot because it requires several hours of class time at the cost of displacement of other basic material. A simple but effective method is now available that has been used successfully at Penn State since Spring 2005. It requires minimal instructor preparation time and only about one class period. Namely, immediately after solving the Navier-Stokes equation analytically for simple flows such as Couette and Poiseuille flow, CFD is introduced as a modern tool for solving the same equations numerically. The application of CFD (grid generation, boundary conditions, etc.), rather than numerical algorithms, is stressed. Homework problems are then assigned using pre-defined templates for FlowLab, a student-friendly analysis and visualization package created by Fluent, Inc. The templates and exercises are designed to support and emphasize the theory and concepts taught in class and in the textbook. For example, the new textbook by Cengel and Cimbala (McGraw-Hill 2006) contains 46 end-of-chapter homework problems that are used in conjunction with 42 FlowLab templates. Each exercise has been designed with two major learning objectives in mind: (1) enhance student understanding of a specific fluid mechanics concept, and (2) introduce the student to a specific capability and/or limitation of CFD through hands-on practice. [Preview Abstract] |
Sunday, November 20, 2005 5:54PM - 6:07PM |
EG.00009: Fluid dynamics code verification based on linear stability analysis Georgios Matheou, Carlos Pantano, Paul Dimotakis Verification of fluid dynamics solvers is the process of demonstrating that a model, such as a set of partial differential equations with its boundary and initial conditions, is solved correctly by a computer code. Computational fluid dynamics code verification techniques include grid convergence, order of accuracy, Richardson extrapolation, and comparison to benchmark solutions. While the latter is particularly valuable, the number of analytical solutions of the Euler or Navier-Stokes equations is limited. The alternative approach employed here utilizes linear stability analysis results. Unfortunately, such solutions can exhibit spatially or temporally localized variations that are much larger than the typical values in most of the domain. For these cases, the usual error metrics tend to perform poorly. We discuss alternative metrics that can be used for code verification in the case of unstable flows and demonstrate this with the spatial instability of a compressible shear layer. [Preview Abstract] |
Sunday, November 20, 2005 6:07PM - 6:20PM |
EG.00010: A One-Dimensional Conservative Method for Front-Tracking in a Compressible Medium Caroline Gatti-Bono, Phillip Colella, Gregory H. Miller, David Trebotich We present a one-dimensional front-tracking algorithm in a compressible medium that can readily be extended to multiple dimensions. The moving interface cuts out time-varying control volumes and a consistent finite-volume discretization is derived by applying the divergence theorem in space-time. The method is fully conservative, even at discontinuities, and the truncation error is expected to be first-order at the boundary between the two fluids, which is one order higher than conventional methods. Classical benchmark results and convergence studies are presented. Target applications for this work are flames in Type 1A supernovae and gas jet boundaries in plasma-wakefield particle accelerators. [Preview Abstract] |
Sunday, November 20, 2005 6:20PM - 6:33PM |
EG.00011: Approximation of the magneto-hydrodynamic equations with a new spectral-FEM method Raphael Laguerre, Caroline Nore, Jacques Leorat, Jean-Luc Guermond We have developed a numerical code in order to solve the equations of the magneto-hydrodynamic in 3-D in the approximation of kinematic dynamo using a new hybrid spectral-FEM method. We have studied the induction effects in different configurations. The understanding of the so-called dynamo effect is our objective and the configurations presented are linked to this effect. [Preview Abstract] |
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