Direct numerical simulation of supersonic boundary layer transition induced by tunnel acoustic radiation

The prediction of the laminar-to-turbulent transition location is vital in the design of hypersonic vehicles, since it affects the heat transfer and drag on the vehicle. The freestream disturbance composition is a crucial input to the problem but is difficult to characterize experimentally. In this work, numerically generated, spatially developing wall turbulent boundary layer data in a supersonic channel at Mach 2.5 are employed with a data-driven technique to extract the spectral makeup of the acoustic radiation. These modeled disturbances are then used to study the transition from receptivity to breakdown stages on a canonical adiabatic flat plate configuration. The freestream slow acoustic waves induce multiple oblique first mode waves in the boundary layer which amplify according to the linear theory. This is followed by the distortion of spanwise vorticity by the growth of secondary instabilities via oblique and asymmetric sub-harmonic resonance mechanisms. Positive and negative streaks are generated, with hairpin vortices developing predominantly on the latter. Turbulent spots are generated intermittently due to the interaction of multiple instability waves, which merge leading to turbulence onset.