Control of Reflected Waves with Acoustic Metasurfaces for Hypersonic Boundary-Layer Stabilization

Stabilization of the Mack second mode is of great significance to control hypersonic boundary-layer transitions. Based on the generalized Snell's law, this work proposes a reflection-controlled metasurface that can restrain the Mack second mode instability by controlling the reflection directions of disturbance waves and consequently stabilize hypersonic boundary-layer flow. The metasurface is periodically corrugated with subwavelength groove groups: each of which is composed of several grooves with different depths. The direct numerical simulation results of a Mach 6 flat-plate boundary layer indicate that the reflection-controlled metasurfaces divide the "two-cell" structure of the Mack second mode into several small parts, and that largely inhibits the growth of the Mack second mode.