A coupled approximate deconvolution and dynamic mixed scale model for large-eddy simulation

Large-eddy simulations of incompressible Newtonian fluid flows with approximate deconvolution models based on the van Cittert method are reported. The Legendre spectral element method is used for the spatial discretization to solve the filtered Navier--Stokes equations. A novel variant of approximate deconvolution models blended with a mixed scale model using a dynamic evaluation of the subgrid-viscosity constant is proposed. This model is validated by comparing the large-eddy simulation with the direct numerical simulation of the flow in a lid-driven cubical cavity, performed at a Reynolds number of 12'000. Subgrid modeling in the case of a flow with coexisting laminar, transitional and turbulent zones such as the lid-driven cubical cavity flow represents a challenging problem. Moreover, the coupling with the spectral element method having very low numerical dissipation and dispersion builds a well suited framework to analyze the efficiency of a subgrid model. First- and second-order statistics obtained using this new model are showing very good agreement with the direct numerical simulation. Filtering operations rely on an invertible filter applied in a modal basis and preserving the C0-continuity across elements. No clipping on dynamic parameters was needed to preserve numerical stability

Can a Helmholtz solver run on a cluster?

Our vectorized Helmholtz solver runs at 85% efficiency on a NEC SX-5. The most time-consuming parts have been ported on SMP, NUMA, and cluster architectures. It is shown that an OpenMP version can deliver similar performance when running it on a 16 processor SGI Altix. A partial parallelisation using MPI is made to validate the Gamma model to predict application behaviours on parallel machines. This model is then applied to simulate the behaviour of a hypothetical full MPI version on different distributed memory machines. It is found that only the Cray XT3 with its very fast internode communication network will be able to deliver the performance of a NEC SX-8 with the advantage that bigger case could be handle