Rarefaction effects on hypersonic boundary-layer stability over a blunt cone at varying degrees of wall cooling and nose bluntness in near-continuum regime
Phys. Rev. Fluids 10, 093901 – Published 4 September, 2025
DOI: https://doi.org/10.1103/7yp5-l4dl
Abstract
This study systematically investigates the hypersonic near-continuum boundary-layer stability over a blunt cone at varying degrees of wall cooling and nose bluntness, offering insights into the rarefaction effects on linear stability mechanisms. The freestream conditions are Mach 8 at an altitude of 50 km. To accurately capture the local rarefaction effects, the slip boundary conditions and nonlinear constitutive relations are incorporated into the conventional Navier-Stokes (NS) equations and linear stability theory (LST) to compute the base flow and perform linear stability analysis. The effects of surface slip and shear nonequilibrium on the base flow and stability at varying wall-cooling degrees and nose bluntness are clarified. The results show that rarefaction effects lead to a thinning of the boundary layer in terms of base flow, primarily due to the influence of velocity-slip and shear nonequilibrium effects. Increasing the wall temperature largely enhances the slip effects at the wall, and decreasing the nose bluntness significantly intensifies the shear nonequilibrium effect in the boundary layer. As for stability, rarefaction effects stabilize the second-mode instability, and this stabilizing influence becomes more pronounced at higher wall temperatures or smaller bluntness. Detailed analyses reveal that velocity-slip plays a dominant role in stabilizing the second mode by modifying the steady base flow, whereas temperature-jump and shear nonequilibrium effects have comparatively weaker contributions. Furthermore, both bluntness and rarefaction contribute to stabilizing near-continuum boundary layer. However, the delay in second-mode critical locations induced by rarefaction effects is significantly greater than that caused by increased bluntness, particularly at lower Reynolds numbers based on bluntness in the near-continuum regime.
