A thermoacoustic heat pump driven by acoustic waves in a hypersonic boundary layer

Abstract

Acoustic waves existing in hypersonic boundary layers act as a heat pump that transfers energy from the sonic line to the wall causing the wall temperature to rise, which explains the newly identified aerodynamic heating related to Mack's second mode from the perspective of thermoacoustic effects. The analysis of data from direct numerical simulations shows that Mack's second mode, belonging to the family of trapped acoustic waves, is highly amplified in a Mach 6 boundary layer and becomes sufficiently strong to affect the mean wall-normal temperature gradient, and the energy transport in the wall-normal direction due to the thermoacoustic effect balancing the thermal conduction brought by the additional temperature gradient.