DNS of Acoustic Receptivity and Breakdown in a Mach 6 Flow over a Generic Forebody

Direct numerical simulations (DNS) of the Navier-Stokes equations have been performed to investigate the receptivity and breakdown mechanisms in a Mach 6 flow over a generic forebody geometry with freestream acoustic disturbances. The simulations are based on transition experiments carried out in April 2015 in the Boeing/AFOSR Mach 6 quiet tunnel facility at Purdue university (BAM6QT). A three-dimensional model for both fast and slow freestream acoustic waves with multiple frequencies and spanwise wavenumbers has been adopted in the numerical simulations, for which high-amplitude disturbances have been considered in order to simulate noisy wind tunnel conditions. The numerical results reveal similarities in comparison to the experimental observations, especially when slow acoustic waves are considered as freestream disturbances. In particular, slow acoustic waves have been found to induce the breakdown process via crossflow instabilities located in the off-centerline region, with formation of streamwise streaks. Fast acoustic waves, in contrast, appear more efficient in inducing earlier nonlinear growth through destabilization of the boundary layer along the symmetry plane of the body.