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 R5: CFD VII: Immersed Boundary Methods |
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Chair: Jianming Yang, University of Iowa Room: 308 |
Tuesday, November 22, 2011 12:50PM - 1:03PM |
R5.00001: An implicit ghost-cell immersed boundary method with mass source and sink for simulations of moving-body problems with control of spurious pressure oscillations Jinmo Lee, Donghyun You For moving body problems where the conventional immersed-boundary methods are employed, the simulation results are often contaminated by spurious pressure oscillations. The spurious pressure oscillations are known to be produced by the violation of mass conservation across interfaces between fluid and moving bodies and to be a function of mainly the grid spacing and time-step size. In the present work, we develop a new immersed boundary method which can control and significantly reduce the spurious pressure oscillations. A ghost-cell immersed boundary method is coupled with a mass source and sink algorithm to better conserve mass around boundary interfaces. A fully-implicit time integration scheme is employed for enhanced control of the time- step size thereby allowing better control of the spurious force oscillations on given mesh resolution. A novel method for treating multiple fresh and dead cells due to the use of a large time-step size is also developed. The present fully-implicit ghost-cell immersed boundary method coupled with a mass source/sink algorithm is demonstrated to significantly reduce spurious pressure oscillations thereby providing accurate and stable solutions for moving body problems. [Preview Abstract] |
Tuesday, November 22, 2011 1:03PM - 1:16PM |
R5.00002: A volume penalization method for incompressible flows and scalar advection-diusion with moving obstacles Kai Schneider, Benjamin Kadoch, Dmitry Kolomenskiy, Philippe Angot A volume penalization method for imposing homogeneous Neumann boundary conditions in advection-diffusion equations is presented. Thus complex geometries which even may vary in time can be treated efficiently using discretizations on a Cartesian grid. A mathematical analysis of the method is conducted first for the one-dimensional heat equation which yields estimates of the penalization error. The results are then confirmed numerically in one and two space dimensions. Simulations of two-dimensional incompressible flows with passive scalars using a classical Fourier pseudo-spectral method validate the approach for moving obstacles. The potential of the method for real world applications is illustrated by simulating a simplified dynamical mixer where for the fluid flow and the scalar transport no-slip and no-flux boundary conditions are imposed, respectively. [Preview Abstract] |
Tuesday, November 22, 2011 1:16PM - 1:29PM |
R5.00003: A hybrid Pseudo-spectral Immersed-Boundary Method for Applications to Aquatic Locomotion Zheng Ren, David Hall, Kamran Mohseni A hybrid pseudo-spectral immersed boundary method is developed for application in marine locomotion. Spatial derivatives are calculated using pseudo-spectral method while a 2nd-order Runge-Kutta scheme is used for time integration. The singular force applied on the immersed boundary is obtained using a direct forcing method. To avoid Gibb's phenomenon in the spectral method, we regularize the force by smoothing it over several grid cells. This method has the advantage of spectral accuracy and the flexibility to model irregular, moving boundaries on a Cartesian coordinate without complex mesh generation. The method is applied to examine locomotion of jellyfish for both jetting and paddling jellyfish. [Preview Abstract] |
Tuesday, November 22, 2011 1:29PM - 1:42PM |
R5.00004: Wall-models for immersed-boundary methods Antonio Posa, Elias Balaras Immersed boundary (IB) methods, where the requirement for the computational grid to conform to solid boundaries is relaxed, have been widely used in a variety of applications. In the majority of cases IB methods are usually coupled to Cartesian solvers, and tackle low to moderate Reynolds number problems. Applications at high Reynolds numbers are prohibitively expensive since an increase in the wall-normal resolution can only be achieved by refining the computational grid in all coordinate directions. A solution to this problem is the development of wall-models for IB methods that can compensate for the luck of resolution in both laminar and turbulent regimes. In the present study we propose novel wall treatment based on a two-layer zonal approach, where the solution of a simplified set of equations is solved near the wall for the purpose of providing an accurate estimate of the near wall flow using information form the coarse underlying Navier-Stokes grid. Various models based on different levels approximation will be presented. Results will be shown for canonical cases such as the flow around a smooth cylinder and around a sphere at various Reynolds numbers. [Preview Abstract] |
Tuesday, November 22, 2011 1:42PM - 1:55PM |
R5.00005: Fluid-Structure Interaction for Flapping Flexible Wings with Large Mass Ratio Min Xu, Mingjun Wei A strong-coupling approach has been successfully used in our previous study for the fluid-structure interaction of flapping flexible wings. However, when the mass ratio of wing and fluid is considered, we are facing a problem to solve Poisson equation with discontinuous coefficients. As the mass ratio increases, normal algorithm for solving the above equation becomes costly and unstable. In this work, we applied the Black Box Multigrid Conjugate Gradient Preconditioned Method (Box-MGPCG) and a smoothing function to overcome the problem. The new algorithm shows consistent efficiency for mass ratio up to 1000. Therefore, it allows us to study the effect of large mass ratio to the performance of flapping flexible wings. Simulation results are also presented here. [Preview Abstract] |
Tuesday, November 22, 2011 1:55PM - 2:08PM |
R5.00006: Simulation of flow over a sphere in a boundary layer using a GPU accelerated IB-LBM Wonho Bae, Jung-il Choi Numerical simulations of flow over a sphere embedded in a laminar boundary layer are conducted for characterizing the effects of wall proximity on the drag and lift forces acting on the sphere. The wall proximity is defined as the distance from the wall to the center of sphere. We utilize an immersed boundary-lattice Boltzmann method (IB-LBM) with a multi-direct forcing technique (Suzuki \& Inamuro, Computers \& Fluids 2011) and combine the present method with a multi-block method (Yu et al., IJNMF 2002) for refining lattices near the sphere. We implement the present IB-LBM into a Graphical Processing Unit (GPU) using a PGI CUDA Fortran programming environment for accelerating the computations. We perform benchmark tests based on simulations of flow over a sphere in a free-stream for validations of the present IB-LBM and evaluations of the performance of the GPU implementation. The results of the drag and lift forces on the sphere according to the wall proximity will be shown in the final presentation. [Preview Abstract] |
Tuesday, November 22, 2011 2:08PM - 2:21PM |
R5.00007: Gust effects on a freely falling plate Hui Wan, Haibo Dong, Zongxian Liang Depending on the Reynolds number and the Froude number, a freely falling plate usually performs one of the following four types of motion, flutter, tumble, steady or chaos fall. It is interesting to know that if and how a gust changes the falling status of a plate. In this work, Direct Numerical Simulations (DNS) will be conducted to study the effects of gust on the freely falling plate by varying the gust amplitude, frequency, and phase relative to the falling plate. Especially, for a plate lies in the chaotic (transitional) region, how its motion be affected as a response to the gust will be discussed. [Preview Abstract] |
Tuesday, November 22, 2011 2:21PM - 2:34PM |
R5.00008: Three-dimensional simulations of the compressible, low-Reynolds number, flow around a hohlraum in a fusion chamber Hasib Uddin, Carlos Pantano, Gwen Loosmore Three-dimensional immersed interface simulations of the flow around a hohlraum in a fusion chamber will be presented. The high injection velocity of the hohlraum results in important compressibility effects while the Reynolds number is quite low due to the high temperature in the chamber (up to 8000K); still well within the continuum limit. A stable recirculation region forms behind the object. In addition, the hohlraum surface temperature is very low to preserve the hydrogen pellet at cryogenic conditions. These conditions are not commonly encountered in flows around blunt objects since high Mach number usually implies high Reynolds number. We study the effects of spin rate at different angles of attack and free flight dynamics. The formation of near surface secondary flow patterns is discussed as well as the distribution of the heat flux. [Preview Abstract] |
Tuesday, November 22, 2011 2:34PM - 2:47PM |
R5.00009: A Hybrid Immersed Boundary-Immersed Interface Method for Cell Tracking in Microdevices Mohammad Hossan, Prashanta Dutta, Robert Dillon The manipulation of cells in microfluidic devices has become routine for biomedical applications such as cell sorting and trapping. To date most of the designs used for cell manipulation are based on experimental trial and error. A fast and accurate numerical algorithm can provide important insight into the design of these devices. In this study, a hybrid immersed boundary-immersed interface method is developed to study the complex behavior of cells in liquid. The immersed boundary method provides an accurate prediction of particle motion in a fluid while the immersed interface method gives second-order accurate solutions for the ion concentrations and electrostatic potential in the presence of moving cells. Both methods employ a fixed computational grid without the need for remeshing at each time step. Cells of different size, shape and charge are allowed to move under both hydrodynamic and electrokinetic forces. Moreover different channel geometries are considered to obtain the best trapping and separation performance. The present immersed boundary-immersed interface model is particularly suitable for bioMEMS devices as this method can accurately predict viscous and electrostatic forces as well as particle velocity, location, and particle membrane deflection. [Preview Abstract] |
Tuesday, November 22, 2011 2:47PM - 3:00PM |
R5.00010: Large Eddy Simulation of Motion-Induced Contaminant Transports in Room Compartments Jung-il Choi, Jack Edwards Large eddy simulation (LES) of contaminant transports due to complex human and door motions is conducted for characterizing the effect of the motion-induced wakes on the contaminant transports in room compartments where a contaminated and clean room are connected by a vestibule. We utilize a LES technique with an immersed-boundary method for moving objects (Choi et al., JCP 2007; Choi and Edwards, Indoor Air 2008) and extend the technique to include Eulerian descriptions of gas-phase contaminant transport as well as thermal energy transfer. We demonstrate details of contaminant transport due to human- and door-motion induced wake development during a short-duration event involving the movement of a person (or persons) from a contaminated room, through a vestibule, into a clean room. Parametric studies that capture the effects of human walking pattern, door operation, over-pressure level, and vestibule size are systematically conducted. The results of parameteric studies will be shown in the final presentation. [Preview Abstract] |
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