Early stage evolution of naturally developing Görtler streaks

Abstract

This is a companion paper to a previous study of hypersonic boundary layer transition over a concave wall [Huang et al., “Inner structures of Görtler streaks,” Phys. Fluids 33, 034116 (2021)]. Experiments are performed in a Mach 6.5 quiet wind tunnel using CO2-enhanced filtered Rayleigh scattering flow visualization, PCB fast-response pressure sensors, and a high-frequency Schlieren technique to investigate naturally developing Görtler streaks. This is the first time that naturally developing Görtler streaks have been visualized using the Rayleigh scattering technique in a hypersonic flow. The results show that three-dimensional waves can be clearly visualized inside the Görtler streaks. More importantly, these waves are amplified owing to Görtler instability, contributing to the formation of Görtler streaks and mushroom-like structures. Thus, the three-dimensional waves can be considered to be basic structures inside Görtler streaks and to play a crucial role in boundary layer transition.