An experimental study on the effects of sharp cone temperature variation on high-speed boundary layer instability

High-speed boundary layer transition directly affects the aerodynamic force and aerodynamic design of high-speed vehicles, yet the physical mechanisms by which local wall temperature variations act upon boundary layer instability, particularly the quantitative effects of tip temperature on the nonlinear evolution of second-mode instability waves and the resulting transition location, remain insufficiently understood through systematic experiments. In this study, experiments were conducted in a Mach 6 Ludwieg tube wind tunnel using a 7° half-angle sharp cone model at zero angle of attack, with high-frequency pressure sensors, a high-speed infrared camera, and a focused laser differential interferometer employed for measurements. The experimental results indicate that when the region of tip temperature variation is located upstream of the synchronization point, cooling the cone tip (to 240 K) enhances the nonlinear interaction of the second-mode instability waves, increasing the critical layer height within the boundary layer by 25% and the maximum amplitude by 79%–88%, while delaying the transition location from 340 mm to 340–360 mm. Conversely, heating the cone tip (to 330 K) suppresses the nonlinear interaction, reducing the critical layer height by 25% and the maximum amplitude by 13%–32%, with the transition location advancing to 313–340 mm. Infrared measurements further demonstrate that tip cooling reduces the surface temperature difference at transition, whereas tip heating produces the opposite effect. This study provides quantitative data support for the thermal protection and aerodynamic design of high-speed vehicles.