Abstract
The compressible bi-global linear stability theory (B-LST), based on two-dimensional eigenfunctions in flow crossplanes, as well as direct numerical simulation (DNS) are applied to investigate the stability properties of three-dimensional laminar hypersonic boundary-layer flows with discrete surface roughness. The obliquely-placed fence-like roughness element has a height of half the unperturbed thermal boundary-layer thickness at its position on the flat plate. The roughness setup is derived from a Space Shuttle flight experiment. A cold-flow non-reacting gas case at wind-tunnel conditions with Mach 4.8 is considered. The laminar steady base flow is extracted from a (D)NS base-flow solution assuming perfect-gas behavior. Local and integral growth of instabilities in the wake of the discrete roughness element are investigated revealing a considerable persistent amplification in the flow. The cold-flow results are compared to a recent instability analysis of a hot-flow, reacting gas case with identical Mach number and roughness geometry. A full DNS of the cold-flow case validates the B-LST results: The growth of the excited disturbance modes shows good agreement. Performance data for the applied codes running on the NEC SX-9 and CRAY XE6 are given.
Published Version
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