声学超表面抑制高速边界层内宽频不稳定模态研究

The influences of the admittance phase and amplitude of acoustic metasurfaces on the broadband unstable modes in a high-speed flat plate boundary layer are analyzed using linear stability theory (LST). It is demonstrated that when the admittance phase goes to 0.5 π, the first mode is suppressed while the second mode is simultaneously motivated. Moreover, the increase of amplitude within the lower frequency range can enhance the stability of the first mode. The Mack second mode is suppressed when the admittance phase tends to π, while the first mode is motivated. Generally, the larger the admittance amplitude is, the more obvious the suppression or excitation effect of unstable modes becomes. Besides, combined with the effect of aperture geometry parameters on the admittance, an engineering realizable broadband acoustic metasurface is proposed to suppress both the first and Mack second modes in Mach 4 boundary layer flow. It elaborately designs the piecewise microstructures to achieve the local favorite admittance phase and amplitude, and its performance is verified by the e^N method.