Numerical and experimental investigation of crossflow instability modes over a yawed cone at Mach 6 by porous surfaces

In this paper, the wind tunnel experiment and parabolic stability equation (PSE) have been used to study the effect of porous surface on hypersonic boundary layer transition over the sharp cone at a 6° angle of attack. Infrared thermography was employed to visualize streak structures induced by stationary crossflow vortices on both the smooth and porous surfaces. Compared to the solid wall, the porous surface slightly enhances the intensity of the stationary crossflow vortices. However, it significantly suppresses high-frequency instabilities while stimulating the low-frequency instabilities, especially the traveling crossflow vortices in the yawed cone boundary layer. The PSE results demonstrate that the high-frequency oblique modes have a higher growth rate than the Mack modes of a sharp cone at a 6° angle of attack. The continuous wavelet transform analysis reveals two high-frequency unstable modes (y-mode and z-mode) on the solid wall, while only one is present on the porous surface. Through bispectrum analysis, it is found that the porous surface exhibits stronger interactions between high-frequency and low-frequency unstable modes, with no observed self-interactions among high-frequency modes.