Phase angle of porous coating admittance and its effect on boundary-layer stabilization

Abstract

Passive control of hypersonic boundary-layer transition using feltmetal and regular porous coatings has recently motivated many researches. The stabilization effects of porous coating on hypersonic boundary layers over flat plates and cones has been demonstrated by theoretical analyses, experiments, and numerical simulations. Previous results showed that both feltmetal and regular porous coatings significantly stabilize Mack’s second mode, whereas Mack’s first mode is moderately destabilized by porous coatings. Up to now, there is no work reported on how to deal with the first mode destabilization and increase the stabilization efficiency of porous coating. In this paper, we analyzed the porous coating admittance and noticed it was the phase angle of admittance that induces the phase discrepancy between the velocity and pressure perturbations on the wall. The effect of the admittance phase angle on Mack’s first mode destabilization and Mack’s second mode stabilization is then studied by series of numerical simulations for artificial porous coatings. The results showed that the phase angle of porous coating admittance has a critical role on boundary-layer stabilization. Specifically, the destabilization of Mack’s first mode is closely related to the phase angle of porous coating admittance, i.e., the destabilization effect decreases with the phase angle of admittance decreasing. The relation between admittance phase angle and first mode destabilization is quite useful for the design of new porous coating.