Crossflow-Induced Breakdown and Transition Correlation for a Hypersonic Swept Plate Flow

The crossflow-induced transition for a Mach 6 flow over a swept plate with a 35 mm nose radius and a sweep angle of 45 deg is investigated using direct numerical simulations (DNSs). In order to shed light on the complete transition process, the evolution of a stationary crossflow wave is first simulated. Then, unsteady wall blowing/suction perturbations are introduced to trigger transition to turbulence. The results show that both the type I and III secondary modes are excited, and they subsequently undergo a linear stage of amplification before breakdown. The type II mode is undetected despite its amplification predicted by the two-dimensional eigenvalue stability approach. Overall, the type I mode achieves a dominant amplitude and plays a key role in the transition. Furthermore, a transition correlation method is proposed based on the dominant secondary instability and threshold amplitude concept, and in order to verify and calibrate it, wall perturbations with different amplitudes are introduced to mimic the varying intensities of the background noise. The transition locations predicted by the most amplified secondary mode agree well with those by DNSs, validating the secondary-instability-based criterion for hypersonic crossflow transition.