Stabilization effect of acoustic metasurfaces on broadband disturbances in a Mach 6 boundary-layer flow

In this study, acoustic metasurfaces are optimized to suppress broadband frequencies of unstable modes in a Mach 6 boundary-layer flow. The metasurface is cut into five pieces, and geometrical parameters of each piece are optimized to afford a comprehensive admittance response to the local frequencies of the first and second modes. It shows the designed broadband metasurface not only is advantageous for stabilizing disturbances above the metasurface region but also inhibits the fast growth rate of low-frequency disturbances on the downstream smooth wall.