DNS of transition in hypersonic boundary-layer flows including high-temperature gas effects

Wind-tunnel experiments at hypersonic Mach numbers above 10 are extremely difficult to undertake and facilities are limited. Additionally, the stagnation conditions for free flight under atmospheric conditions can not be reproduced. This results in a limited portability of the wind-tunnel results to atmospheric conditions. Therefore, numerical investigations of hypersonic transition can be extremely valuable in developing an understanding of the transition process at hypersonic speeds. The objective of this effort is to develop an understanding of effects of nonequilibrium chemistry on transition. Our approach is to compare hypersonic transition on a flat plate under nonequilibrium chemical and thermal conditions to hypersonic transition under equilibrium conditions. In the 1950’s and 60’s, a series of hypersonic experiments was conducted in free flight. The transition location could be found but no details on the transitional structures could be recorded in these experiments (see Schneider, 1999, for a comprehensive review of supersonic and hypersonic experiments). Schneider also notes that the angles of attack of the test vehicles are uncertain. An ongoing experiment on transition at Ma = 21 in Novosibirsk, Russia Mironov & Maslov 2000, promises experimental verification of the numerical findings to some extent. Further detailed experiments on transition at hypersonic speeds cannot be expected in the near future.