Assessment of Unstructured Grids for Detached- Eddy Simulation of High Reynolds Number Sepa- rated Flows

An assessment of unstructured grids for use in Detached-Eddy Simulation (and more generally in Large-Eddy Simulation) of massively separated ows is presented. The role of the grid, its generation and re nement, are considered via calculation of three high-Reynolds number turbulent ows of aerodynamic interest: the massively separated ow over a forebody in cross ow, the ow over a delta wing at 27Æ angle of attack, and the ow around an F15E at 65Æ angle of attack. Unstructured grids are generated using Gridgen and VGRIDns and are evaluated against guidelines proposed by Spalart[4], which outline the unique requirements of Detached-Eddy Simulation grids. For each geometry, the grids are characterized by a \viscous region" comprised of prism layers, with the \focus region" formed from nearly-isotropic tetrahedra. Predictions of the ow around the forebody show qualitatively similar wake structures, and very close pressure distributions obtained using structured and unstructured grids. Extensive grid re nement is performed for the delta wing and the F-15E, with systematic re nement accomplished via straightforward changes to a grid control parameter. Baseline grids are re ned and coarsened by p 2 in all three coordinate directions, and the time step is varied by the same scale factor. A tangibly wider range of turbulent length scales is captured on the ner grids, with the coarser grids also showing a reasonable scale range. The capability of unstructured grids to meet Spalart's[4] guidelines and the ability to rapidly re ne these grids to reduce numerical errors is demonstrated.