Delayed Detached-Eddy Simulation of Subsonic Axisymmetric Base Flow

Abstract

Axisymmetric base flow is investigated to understand flow physics associated with the massive flow separation at a subsonic speed. The detached-eddy simulation (DES) approach is well suited in the current separated flow with a known separation point. The upstream attached boundary layer is well represented with the Reynolds-averaged Navier-Stokes (RANS) mode, whereas the separated flow from the base is well captured in the large-eddy simulation (LES) mode. Since the spatial resolution in the LES zone impacts directly the fidelity of the DES computation, a systematic approach is applied to the computational grid. Current computational grids are designed for nearly isotropic grids in the separated region (i.e., LES zone) with much reduced anisotropy of the grid in the separating shear layer, compared to computational grids documented in literature. Current grids allow the separating shear layer to undergo the Kelvin-Helmholtz instability, resulting in a rapid shift from the RANS to LES mode right after the flow separation. In consequence, the axisymmetric base flow is well resolved in the current DES computation with good agreement to relevant experimental data including the mean base pressure and the center-line velocity in the wake. The base flow is further discussed with statistical data of the separated flow. Current DES simulation is also compared with a typical RANS simulation to emphasize the high fidelity of the computational approach.