Review of acoustic metasurfaces for hypersonic boundary layer stabilization

Hypersonic boundary layer (BL) transition generates a significant increase in viscous drag and heat flux, which leads to severe restrictions on the performance and thermal protection systems of hypersonic vehicles. Among various passive/active transition control strategies, acoustic metasurfaces demonstrate minimal effects on the mean flow but significantly suppress the Mack second mode. Therefore, it can be considered one of the most promising transition control technologies. Acoustic metasurfaces are planar metamaterial structures that comprise monolayer or multilayer stacks of subwavelength microstructures, which affect unstable modes via acoustic wave manipulations. This paper presents a review of the research progress made on acoustic meta surfaces for hypersonic BL stabilization over the past two decades. Acoustic characteristics and their corresponding stabilization effects on the first and second modes are compared and discussed. Recent improvements in the mathematical modeling of acoustic metasurfaces have been highlighted. An outline of the theoretical, numerical, and experimental investigations is then provided. Finally, a future research potential, especially for broadband design strategies and full direct numerical simulations, is prospected.