The Influence of Rotational and Vibrational Energy Relaxation on the Stability of Boundary-Layers in Supersonic Flows

Kurzfassung

The influence of rotationa and vibrational energy relaxation on the stability of laminar boundary layers at supersonic flow velocities is investigated. The relaxation times are derived from published experimental data in the field of physical chemistry. The influence of rotational relaxation is to dampen high-frequency instabilities, consistent with the well known damping effect of rotational relaxation on acoustical waves. The influence of rotational relaxation can be modeled through a bulk-viscosity coefficient with a new temperature dependence that is different from that of the shear viscosity. Vibrational relaxation affects the laminar base flow, strongly destabilizing both first and second mode instabilities on body geometries that have a blunt leading edge, and on geometries with a sharp leading edge in wind-tunnel flows. The influence is weak only for the idealized plate with infinitely thin thickness in free-flight conditions.