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SUMMARYThe analysis and improvement of an immersed boundary method (IBM) for simulating turbulent ows over complex geometries are presented. Direct forcing is employed. It consists in interpolating boundary conditions from the solid body to the Cartesian mesh on which the computation is performed. Lagrange and least squares high-order interpolations are considered. The direct forcing IBM is implemented in an incompressible ÿnite volume Navier-Stokes solver for direct numerical simulations (DNS) and large eddy simulations (LES) on staggered grids. An algorithm to identify the body and construct the interpolation schemes for arbitrarily complex geometries consisting of triangular elements is presented. A matrix stability analysis of both interpolation schemes demonstrates the superiority of least squares interpolation over Lagrange interpolation in terms of stability. Preservation of time and space accuracy of the original solver is proven with the laminar two-dimensional Taylor-Couette ow. Finally, practicability of the method for simulating complex ows is demonstrated with the computation of the fully turbulent three-dimensional ow in an air-conditioning exhaust pipe.

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The performance of an hybrid LES-RANS strategy, the Detached Eddy Simulation (DES), as a predictive tool for turbulent channel flow with massive separation is scrutinized. This is undertaken in a collaborative effort involving five different flow solvers used by five different groups to cover a broad range of numerical methods and implementations. This paper concentrates on DES results obtained with a computational mesh of approximately one million cells. The results are compared to those obtained by Large Eddy Simulations (LES) using the standard and the dynamic Smagorinsky models and an alternative hybrid LES-RANS -all computed on the same grid. Data of a highly resolved LES (roughly 13 million cells) are used for reference. Furthermore, the impact of resolution and, therefore, the location of the LES-RANS interface is studied.

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