Interaction of Ultrasonic Acoustic Waves and Metasurface Structures for Hypersonic Boundary-Layer Stability Applications *

Hypersonic aircraft design is still a challenging problem because of the complex flow physics involved. Prediction and control of the boundary-layer transition from a laminar to a turbulent state is vital to hypersonic vehicles. The boundary-layer transition has a first-order impact on aerodynamic heating, drag force, engine performance, and vehicle operation. Mack’s second mode is an acoustic wave reflecting between the aircraft’s exterior surface and the sonic line in the boundary layer, which acts as an acoustic waveguide. The trapped instability waves gain amplitude, break down, and cause a transition to a turbulent state. This talk will present the interaction between the acoustic waves and several metasurfaces with various geometric shapes. In the numerical simulations, we considered a disturbance wave with a 30-degree incident angle and two frequencies 100 kHz and 400 kHz. We simulate the interactions using the ultrasound module of the COMSOL Multiphysics solver. In the simulations, the background flow is neglected. The reflection ratios are computed in the time and frequency domains. We will present the reflection ratios and the performance of the metasurface designs for future direct numerical simulations (DNS) and experimental studies.