Roughness-Induced Boundary-Layer Transition on a Hypersonic Capsule-Like Forebody Including Nonequilibrium

摘要

The present work investigates the influence of high-temperature gas effects on the laminar-turbulent transition induced by a patch of distributed roughness on a hemispherical capsule-like geometry. The freestream conditions correspond to a realistic reentry scenario at Mach 20. At these conditions, chemical reactions and nonequilibrium effects are present in the high-enthalpy boundary layer of the hemisphere. Parallel Direct Numerical Simulations are undertaken to analyze the instability mechanisms in the crossflow-type vortex developing in the wake of a skewed protuberance of the roughness patch. Both linear and nonlinear growth of unsteady disturbances forced in the roughness wake, including laminar-turbulent breakdown, are considered in the analysis. The primary focus of the study is how chemical and thermal nonequilibrium affect the location of the laminar-turbulent transition as well as the level of wall heating in the transitional boundary layer for the considered capsule configuration. The results highlight the necessity to include nonequilibrium effects in this problem of roughness-induced transition at high-altitude reentry conditions because the gas modeling turns out to have a notable influence on the development of instabilities, both in the linear and in the nonlinear ranges.