Direct numerical simulations of the nonlinear transition regime on a flat plate at mach 6

Direct Numerical Simulations (DNS) were carried out in order to investigate the laminar-turbulent transition process on a flat plate boundary layer at Mach 6. Of particular interest is the nonlinear regime and whether any of the classical nonlinear breakdown mechanisms (fundamental resonance, subharmonic resonance, oblique breakdown) are relevant in the case of a flat plate. The conditions of the Boeing/AFOSR Mach 6 Quiet Tunnel (BAM6QT) at Purdue University were used for the simulations. In order to investigate the relevant breakdown mechanism, the flow is perturbed with a short-duration pulse through a small blowing and suction hole at the wall. The resulting three-dimensional wave packets contain a wide range of frequencies and wavenumbers. The development of the wave packet as it propagates through the computational domain is explored with respect to the linear and the nonlinear regime by forcing with different initial disturbance amplitudes. In addition, the effect of forcing hole dimensions on the initial development of the wave packet downstream of the forcing location was explored.