Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session BB: Computational Fluid Dynamics I |
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Chair: Javid Bayandor, Royal Melbourne Institute of Technology Room: Salt Palace Convention Center 150 D-F |
Sunday, November 18, 2007 10:34AM - 10:47AM |
BB.00001: Computational sensitivity analysis of laminar flows using finite volume methods Richard Kirkman, Meredith Metzger Computational sensitivity analysis is an emerging field of research with the potential to improve the efficiency of parameter studies, provide increased insight during optimization processes, and assess the cascade effect of input uncertainty into numerical data. An unsteady finite volume based fractional step computational fluid dynamics algorithm has been developed and coupled with several common computational sensitivity analysis methods (finite difference, continuous sensitivity equation method, and complex step) to generate local sensitivity coefficients. A survey of these computational sensitivity analysis methods has been performed comparing accuracy, computational efficiency, and ease of implementation. Several examples of sensitivity analysis to parameters associated with the governing equations, as well as parameters associated with geometric extent of the domain and boundary conditions, are presented for several laminar flow fields, including developing flow in a two-dimensional channel and boundary layer flow over two staggered cubes. [Preview Abstract] |
Sunday, November 18, 2007 10:47AM - 11:00AM |
BB.00002: The Pulsed Flow Algorithm (PFA) Applied to Coupled Respiratory and Circulatory Systems A. Staples, E. Oran, J. Boris, C. Kaplan, K. Kailasanath The Pulsed Flow Equations (PFE) are a set of coupled partial differential equations designed to capture features particularly relevant to internal flows through flexible elastic channels, such as flows in physiological systems in biological organisms, and hydraulics systems. The equations are an extension of the standard one-dimensional fluid flow equations that, in addition, are able to capture two-dimensional diffusion, branching, transport, viscous, and other effects. A limiting case of the equations is the standard one-dimensional fluid flow equations. The equations are discretized and solved partially using an asymptotic solution, after which they reduce to tridiagonal form. The solution formalism can be applied to many types of complex networks of internal flows, and solves these problems, including some important two-dimensional effects, at the cost of a one-dimensional tridiagonal computation. Here we apply the PFA to describe a coupled circulatory and respiratory system calibrated to the average human body. [Preview Abstract] |
Sunday, November 18, 2007 11:00AM - 11:13AM |
BB.00003: ABSTRACT WITHDRAWN |
Sunday, November 18, 2007 11:13AM - 11:26AM |
BB.00004: High-order fluid/structure coupled numerical model. Jose Carlos Pereira, Paulo Ferreira de Sousa A coupled fluid-structure method to study the coupled nonlinear problem of flapping aero-elastic structures was developed. The fluid-dynamic solver is a finite-difference solution to the Navier-Stokes equations solved on a grid fitted to a moving thin body. Direct solution of the NavierStokes equations is carried out using a previously developed high-order 2D immersed boundary method on a moving curvilinear grid. Fluid-dynamic forcing on the body surface is calculated and used as input to a finite difference structural-dynamic solver. The structural solver is geometrically nonlinear and able to take on arbitrary configurations. Both solvers are explicit and use a Runge-Kutta 4th order time discretization scheme. Case studies that the coupled fluid/structure method was applied include flag flapping and harmonically pitching flexible membranes with different densities and rigidities. [Preview Abstract] |
Sunday, November 18, 2007 11:26AM - 11:39AM |
BB.00005: A Spectral Quadrilateral Subdomain Penalty Method Model for High Reynolds Number Incompressible Flows Jorge Escobar-Vargas, Peter Diamessis We report our latest results in the development of a novel spectral multidomain penalty method model for the simulation of localized high Reynolds number incompressible flows in doubly non-periodic domains. The target flow for model application is the unstable boundary layer in the footprint of a nonlinear internal wave. Numerical stability, without loss of spectral accuracy, is ensured through the implementation of a penalty scheme and spectral filtering in the Legendre polynomial-based discretization in individual quadrilateral subdomains. The penalty coefficients are computed through a stability analysis based on the energy method. The design of efficient preconditioners for the solution of the 2-D Helmholtz and Poisson equations, in the context of a discontinuous element-based scheme, will be discussed in detail. The efficiency of the penalty model will be illustrated through comparisons with exact solutions of the linear advection-diffusion equation and the shallow water equations. [Preview Abstract] |
Sunday, November 18, 2007 11:39AM - 11:52AM |
BB.00006: An Accurate Time Advancement Algorithm for Particle Tracking Pavel Popov, Stephen Pope We describe a particle-position time-advancement algorithm that is designed for use with several subgrid velocity reconstruction schemes used in LES/FDF methods, and potentially in other applications. These reconstruction schemes yield a subgrid velocity field with desirable divergence properties, but also with discontinuities across grid faces. Therefore, a conventional time advancement algorithm, such as second-order Runge-Kutta (RK2), does not perform as well as it does with a smooth velocity field. The algorithm that we will describe, called Multi-step RK2 (MRK2), builds upon RK2 by breaking up the time step into two or more substeps whenever a particle crosses one or more velocity discontinuities. When used in conjunction with the Parabolic Edge Reconstruction Method, MRK2 performs considerably better than RK2: both the final position of an advected particle, and the final area of an infinitesimal area element are second-order accurate in time (as opposed to first-order accurate for RK2). Furthermore, MRK2 has the theoretical advantage that it preserves the continuity of the mapping between initial and final particle positions. [Preview Abstract] |
Sunday, November 18, 2007 11:52AM - 12:05PM |
BB.00007: An Approximate Analytical Solution for Backward-Facing Step Flow Ismail Celik, Don Parsons, Ertan Karaismail, Jagannath Nanduri Flow past a backward facing step is a classical bench mark for both laminar and turbulent flow calculations. Due to the near-singular behavior arising from the presence of the sharp step, it is very difficult to predict the size of the recirculation region and the reattachment length. This difficulty, in turn, manifests itself as a significant discrepancy between predicted and measured velocity profiles. The aim of the current work is to formulate an analytical solution to the 2D, steady flow in question that satisfies the Navier-Stokes equations with a source term. The proposed solution is a superposition of two stream functions, one being a semi-potential solution that satisfies all the boundary conditions for real incompressible fluids, and another composed of rotational vortices (e.g. Rankine vortices) which enable flow separation. The location and distribution of the vortices is selected to emulate the Reynolds number dependence of the re-attachment length, while other parameters in the model are used to minimize the additional source term that is needed. The proposed solution can be primarily used in code-verification, and quantification of discretization errors in CFD (Computational Fluid Dynamics). It can also be used to assess modeling errors, by adding additional source terms that represent the spatial variations in turbulent-eddy viscosity, the key quantity used in Boussinesq-type turbulence models. [Preview Abstract] |
Sunday, November 18, 2007 12:05PM - 12:18PM |
BB.00008: Prediction of Progressive Decomposition in Launching Space Vehicles Subject to Soft Foreign Object Impacts Javid Bayandor Reusable space vehicles are subjected to high velocity to ballistic foreign object impact (FOI) events, particularly soft impacts. Such events and their consequent severe dynamic loading/unloading conditions occur during the launch phase or landing approach of the re-entry vehicles within their tropospheric flight windows. Effective prediction of non- linear dynamic responses of such structures, accentuated by the intricacy of the transient solid-fluid behavior of the projectile, can play a major role in developing a fail-safe design for these vehicles. A resulting crashworthy design can materialize through active control of the failure sequencing of the primary and secondary components. Two major discretized fluid-solid approaches, Smooth Particle Hydrodynamics (SPH) and Arbitrary Lagrangian-Eulerian (ALE), will be compared and presented which enable the effective prediction of complicated phase transition in the projectile. While the focus will be given to the SPH approach, a novel coupled micro constitutive/cohesive finite element solution will also be introduced, enabling the multi-scale analysis of progressive degradation and disintegration in impacted advanced space composite (sub)structures. [Preview Abstract] |
Sunday, November 18, 2007 12:18PM - 12:31PM |
BB.00009: Solution of Reynolds-averaged Navier-Stokes equations by discontinuous Galerkin method Sungwoo Kang, Jung Yul Yoo Discontinuous Galerkin method is a finite element method that allows discontinuities at inter-element boundaries. The discontinuities in the method are treated by approximate Riemann solvers. One important feature of the method is that it obtains high-order accuracy for unstructured mesh with no difficulty. Due to this feature, it can be useful for various practical applications to turbulence and aeroacoustics, but there are few problems to be solved before the method is applicable to practical flow problems. Due to discontinuous approximations in discontinuous Galerkin method, the treatments of viscous terms are complicated and expensive. Moreover, careful treatments of source terms in turbulence model equations are necessary for Reynolds-averaged Navier-Stokes equations to prevent blow-up of high-order-accurate simulations. In this study, we compare high-order accurate discontinuous Galerkin method with different viscous treatments and stabilization of source terms for compressible Reynold-averaged Navier-Stokes equations. Spalart-Allmaras or k-$\omega $ model is used for turbulence model. To compare the implemented formulations, steady turbulent flow over a flat plate and unsteady turbulent flow over cavity are solved. [Preview Abstract] |
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