Direct Numerical Simulation of Wave Packets in Hypersonic Compression-Corner Flow

Abstract

Direct numerical simulations of a three-dimensional wave packet propagating over a 5.5 deg compression corner at the freestream Mach number 5.373 are carried out. The Navier–Stokes equations are integrated using an implicit finite volume shock-capturing method with the second-order approximation in space and time. After computing the laminar flowfield, unsteady disturbances are imposed onto the steady solution via local suction blowing on the wall surface. The undisturbed boundary layer separates upstream of the corner and reattaches downstream, forming a shallow separation bubble. The suction-blowing pulse generates a three-dimensional wave packet propagating downstream. If the pulse is produced near the leading edge, the wave packet is dominated by oblique waves relevant to the first mode, whereas plane waves of the second mode are relatively small. At sufficiently strong forcing, the nonlinear effects destabilize the wave packet in the separation region and lead to its nonlinear breakdown downstream of the reattachment line. Ultimately, a young turbulent spot is formed in the reattached boundary layer. If the pulse is produced sufficiently far downstream of the leading edge, so that the major portion of the first-mode instability region is not involved, the wave packet is dominated by the second mode. These examples show that the wave-packet contents and its downstream evolution strongly depend on how and where the initial disturbance is excited.