Effect of Local Thermal Strips on Hypersonic Boundary-Layer Instability

Abstract

An effect of localized thermal strips on hypersonic boundary-layer instability is investigated using linear stability theory (LST). The linear evolution of Mack's second mode is analyzed for a Mach 4.5 flat-plate boundary-layer with and without the strips. The validity of the LST analysis is assessed through the comparison of the results with implicit large eddy simulations (ILES) for selected cases. Parametric studies on the temperature intensity, length, and location of a single strip are performed to examine the influence of the strip on the second-mode instability. A reversal in the stabilizing and destabilizing effect according to the local streamwise surface pressure gradient induced by the strip is identified. The reversal point of the stabilizing/destabilizing effect is located in the vicinity of the location of the maximum growth rate of the second mode. The influence of three strips in a series arrangement is also analyzed for several combinations. The proper combination of strips, considering the reversal phenomenon, results in more significant stabilizing/destabilizing effects for a disturbance with a specific frequency. The overall effects are also evaluated and analyzed in terms of the envelope of the N-factor curves by carrying out the LST calculations for disturbances with various frequencies.