Description of the synchronization of the 2nd Mack mode and acoustic waves in highly cooled hypersonic boundary layers by means of AHLNS

Abstract

In high-enthalpy wind tunnels, the wall temperature is significantly smaller than the free-stream temperature. It is well-known that wall cooling promotes the stabilization of the first mode and destabilization of the second mode. Moreover, for sufficiently cooled walls, the unstable modes can travel supersonically with respect to the free-stream. This leads to the synchronization of the second mode with acoustic waves of the continuous spectrum. In the synchronization region, the phase speeds of the discrete unstable mode and the acoustic waves are very similar. This phenomenon is known as spontaneous radiation of sound.