Numerical Investigation of Fin-Induced Mach 5 Laminar Shockwave Boundary Layer Interaction

Depending on the flight Mach number, atmospheric conditions, vehicle geometry and angle of attack, the boundary layer over hypersonic vehicles can be laminar. The interaction of laminar boundary layers with control surfaces such as fins leads to complex unsteady shockwave boundary layer interactions. This paper reports on large-eddy simulations of a blunt and a 15deg swept fin in a laminar Mach 5.15 boundary layer. The simulations model experiments in the Mach 5 shock tunnel at New Mexico State University. Schlieren images obtained from both simulations and experiments are in good agreement. For both cases, the flow field is characterized by laminar separation upstream of the fin, and a pronounced horseshoe vortex. Proper orthogonal decompositions of the schlieren visualizations reveal both low- and high-frequency junction unsteadiness. The unsteadiness is weaker for the swept case. Instantaneous flow visualizations and linear stability theory analysis suggest that shear-layer instability of the separated boundary layer leads to the shedding of two-dimensional vortex structures that are subject to secondary instability.