Exploring the boundary layer transition of hypersonic flow over a compound delta wing

Abstract

The boundary layer transition on a compound delta wing for Mach 6 has been studied experimentally and numerically. The experiment was performed at Peking University quiet wind tunnel using the Rayleigh scattering flow visualization and infrared thermography. Direct numerical simulations, under the same flow conditions, are applied to analyze the transition mechanism. The results show that the traveling cross flow vortices first appear near the leading edge of compound delta wing. These vortices modulate the mean profile of the flow due to which a rope-like structure appear in the streamwise direction, which is typical of Mack's second-mode. As Mack's second-mode grows to a sufficiently large amplitude, it triggers secondary instability, which behaves as secondary finger like structures. At the end of the transition process, low-frequency waves are excited by Mack's second-mode through an interaction mechanism with their phase speed approaching each other. It is also found that increasing the unit Reynolds number greatly promotes the aerodynamic heating as well as local hot streaks appear on both sides of the compound delta wing in the streamwise direction. The appearance of hot streaks on the compound delta wing is strongly correlated with Mack's second-mode.