Fundamental breakdown of second modes

Abstract

Boundary layer transition in a hypersonic flow with a zero-pressure gradient takes on particular properties. Trapped acoustic modes [1], hereafter referred to as second modes, can coexist with first modes. Furthermore, the presence of a highly-cooled wall imparts a high growth rate to the second modes [2] and they dominate first mode growth within the boundary layer [3]. An important aspect in this field is the nature of breakdown of the second modes after they reach saturation within the boundary layer. This process results in the initiation of turbulence. The breakdown region is associated with overshoots in surface heat flux [4]. A physical understanding of the breakdown process is required under conditions of highly-cooled walls. This works aims to contribute to this.