Vortex methods for high-resolution simulations of viscous flow past bluff bodies of general geometry

Recent contributions to the 2-D vortex method are presented. A technique to accurately redistribute particles in the presence of bodies of general geometry is developed. The particle strength exchange (PSE) scheme for diffusion is modified for particles in the vicinity of the solid boundaries to avoid a spurious vorticity flux during the convection/PSE step. The scheme used to enforce the no-slip condition through the vorticity flux at the boundary is modified in a way that is more accurate than in the previous method. Finally, to perform simulations with nonuniform resolution, a mapping of the redistribution lattice is also used. In that case, the PSE is still done in the physical domain, using a symmetrized, conservative scheme. The quadratic convergence of this scheme is proved mathematically, and numerical tests are shown to support the proof. These elements are all validated on the benchmark problem of the flow past an impulsively started cylinder, High-resolution, long-time simulations of the flow past other bluff bodies are also presented: the case of a square and of a capsule at angle of attack. (C) 2000 Academic Press

Simulation of vehicle aerodynamics using a vortex element method

Recent developments of the 3-D Lagrangian vortex element method for bluff body flows are presented. In this approach attached boundary layer regions are modelled using infinitely thin vortex sheets while Lagrangian vortex elements are used for the separation regions and the wake. Preliminary results for the flow past a simplified generic truck geometry are presented. Further developments, aimed at the development of a hybrid Eulerian-Lagrangian solver, are briefly introduced

Vortex particles and tree codes: I. flows with arbitrary crossing between solid boundaries and particle redistribution lattice; II. vortex ring encountering a plane at an angle.

The first part of the paper deals with 2-D vortex methods. We briefly review the numerical method and we extensively describe two points in more details: the redistribution around an arbitrary body and a new scheme to diffuse a vortex sheet onto particles in a way that is most accurate. These two improvements allow to perform DNS of 2-D flows past bodies of arbitrary shape. We test and validate them on the flow past an impulsively started circular cylinder. The second part of the paper is about 3-D flows with solid boundaries. We test the viscous method on the interaction between a vortex ring and a plane. We also detail a modified version of the Particle Strength Exchange (PSE) scheme close to the solid boundary so as to enhance the accuracy of the method. Fast vortex codes are used for both 2-D and 3-D computations. The 3-D code is also parallel

Vortex methods for direct numerical simulation of three-dimensional bluff body flows: Application to the sphere at Re=300, 500, and 1000

Recent contributions to the 3-D vortex methods are presented. Following Cottet, the particles strength exchange (PSE) scheme for diffusion is modified in the vicinity of solid boundaries to avoid a spurious vorticity flux and to enforce a zero-normal component of vorticity during the convection/PSE step. The vortex sheet algorithm used to enforce the no-slip boundary condition through a vorticity flux at the boundary and the technique used to perform accurate redistributions in the presence of bodies of general geometry are extended from their 2-D counterpart. To perform simulations with nonuniform resolution, a mapping of the redistribution lattice is used. Computational efficiency is attained through the use of parallel tree codes based on multipole expansions of vortex particles and of vortex panels. The method is validated, by comparisons with other authors' results, on the flow past a sphere at Re = 300. It is then applied to compute the flow at Re = 500 and 1000. (C) 2002 Elsevier Science (USA)

Simulation of randomly excited acoustic insulation systems using finite element approaches

Acoustic transmission properties of sound-insulating structures play an important role in the design of many transport systems (as, for instance, automotive, aircraft and railway products). Design procedures require efficient computational tools based on the selection of appropriate numerical models for both the insulating structure and the surrounding (bounded or unbounded) acoustic domains. Additionally the description of excitation mechanisms requires some caution and weak or strong coupling effects should be taken into account. The paper presents the main features of a refined finite element approach for addressing acoustic transmission problems in a random context. The model relies on the usual elasto-acoustic approximations. A particular attention is devoted to the description of turbulent boundary layer excitations. The handling of such spatially correlated random excitations is described both in direct (physical) and reduced (modal) contexts. A powerful asymptotic modal formulation is identified. Comparisons with reference analytical solutions are presented and demonstrate the validity of the proposed method. Further application to a reduced scale greenhouse model (from the EC-funded project SMILE) is presented.Anglai

Vortex particles and tree codes: I. flows with arbitrary crossing between solid boundaries and particle redistribution lattice; II. Vortex ring encountering a plane at an angle

The first part of the paper deals with two-dimensional vortex methods. We briefly review the numerical method and describe two points in more detail: the redistribution around an arbitrary body, and a new scheme to diffuse a vortex sheet into particles in a way that is more accurate. These two improvements allow to perform DNS of two-dimensional flows past bodies of arbitrary shape. We test and validate them on the flow past in impulsively started circular cylinder. The second part of the paper is about three-dimensional flows with solid boundaries. We test the viscous method on the interaction between a vortex ring and a plane. We also detail a modified version of the particle strength exchange scheme close to the solid boundary in order to enhance the accuracy of the method. Fast vortex codes are used for both two- and three-dimensional computations. The three-dimensional code is also parallel