Hypersonic Boundary Layer Stability of Local Cooling Strip and Porous Surface

Hypersonic boundary layer transition is one problem the modern aviation world tries to overcome for sustained hypersonic flight. The early laminar to turbulent transition over the air vehicle's body leads to increased heat transfer and aerodynamic drag, which decreases the vehicle's performance. Although thermal protection systems can alleviate the drawbacks, they increase the cost and weight of the aircraft and require frequent maintenance. In the literature, researchers proposed promising solutions to stabilize the instabilities that lead to hypersonic boundary layer transition from laminar to turbulent flow. Local wall cooling is one method that stabilizes Mack's first mode. However, second mode instabilities are the dominant waves in two-dimensional boundary layer flow at hypersonic speeds. The porous surface on the solid wall may stabilize the second mode instabilities. The drawback of porous surfaces is the destabilization in the first mode instabilities. Stabilizing the first mode with the local cooling strip and the second mode with the porous surface may delay the transition significantly. This study developed a high-order linear stability code (HLST) to solve the eigenvalue problem for the combined local cooling and porous surface (LCPS) application. Flow over a flat plate, wedge and cone are solved in hypersonic flow conditions to validate the results with the literature. The similarity solution and a high-order accurate steady flow solver are used to obtain the boundary layer profiles. The effect of the local cooling strip and porous surface on the hypersonic boundary layer is investigated.