Thermochemical Non-Equilibrium Effects on Passive Control of Hypersonic Boundary-Layer Transition Using Regular Porous Coating

Abstract

In the past decade, passive control of hypersonic boundary-layer transition using porous coatings has been studied by theoretical analyses, experiments, and numerical simulations. It was found that porous coating stabilizes Mack’s second mode and destabilizes Mack’s first mode. However, there is only quite limited studies on the stabilization efficiency of porous coating. And no work has been reported about the thermochemical non-equilibrium effects of hypersonic flows on the stabilization efficiency. In this paper, we conduct numerical simulations on the passive control of hypersonic boundary-layer transition using regular porous coating. The stabilization of a Mach 5.92 flat-plate boundary layer is first studied for perfect gas flow. The results show that, at approximately the same porosity, regular coating is weaker in first-mode destabilization and second-mode stabilization than felt-metal coating. The porosity decrease of regular coating leads to even weaker first-mode destabilization and second-mode stabilization. The results also show that the first-mode destabilization weakens as the phase angle of admittance decreases and the thermochemical nonequilibrium of hypersonic flows may affect the stabilization efficiency of regular coating. Therefore, numerical simulations based on perfect gas flow may not be enough. The effects of thermochemical non-equilibrium flow including internal energy excitations, translation-vibration energy relaxation, and chemical reactions among different species need to be considered. We have developed a new high-order shock-fitting solver for non-equilibrium flow simulations based on the 5-species air chemistry and recently thermal non-equilibrium models. The code package has been tested and is being applied to numerical simulation of a Mach 12.56 boundary layer over a blunted wedge of a half angle 20 degree. Thermochemical non-equilibrium effects of hypersonic flows on the steady base flow is investigated by comparing numerical results of perfect gas flows and thermochemical nonequilibrium flow. Unsteady simulations on the passive control of hypersonic non-equilibrium boundary-layer transition using regular porous coating are currently ongoing.