Early stage evolution of naturally developing Gortler streaks

This is a companion paper to a previous study of hypersonic boundary layer transition over a concave wall [Huang et al., Inner structures of Gortler 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 Gortler streaks. This is the first time that naturally developing Gortler 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 Gortler streaks. More importantly, these waves are amplified owing to Gortler instability, contributing to the formation of Gortler streaks and mushroom-like structures. Thus, the three-dimensional waves can be considered to be basic structures inside Gortler streaks and to play a crucial role in boundary layer transition.

Automated summary

This study visualizes naturally developing Gortler streaks using Rayleigh scattering technique for the first time in hypersonic flow, showing that three-dimensional waves play a crucial role in the formation of Gortler streaks and mushroom-like structures.