Hypersonic boundary layer receptivity to acoustic disturbances over cones.

摘要

The receptivity mechanisms of hypersonic boundary layers to free stream acoustic disturbances are studied using both linear stability theory (LST) and direct numerical simulations (DNS). A computational code is developed for numerical simulation of steady and unsteady hypersonic flow over cones by combining a fifth-order weighted essentially non-oscillatory (WENO) scheme with third-order total-variation-diminishing (TVD) Runge-Kutta method. Hypersonic boundary layer receptivity to free-stream acoustic disturbances in slow and fast modes over 5-degree, half-angle blunt cones and wedges are numerically investigated. The free-stream Mach number is 6.0, and the unit Reynolds number is 7.8x106/ft. Both the steady and unsteady solutions are obtained by solving the full Navier-Stokes equations in two-dimensional and axisymmetric coordinates.;Computations are performed in three steps. After the steady mean flow field is computed, linear stability analysis is performed to find the most amplified frequency and the unstable disturbance modes in different flow regions. Then time accurate computations are performed using slow and fast mode acoustic disturbances, and the initial generation, interaction and evolution of instability waves inside the boundary layers are studied.;Receptivity computations showed that the acoustic disturbance waves propagated uniformly to downstream, interact with the bow shock, enter the boundary layer, and then generate the initial amplitude of the instability waves in the leading edge region. Effects of the entropy layer due to nose bluntness to the receptivity process are studied. It is found that transition location moves downstream and is delayed by increasing bluntness, and the role of the entropy layer in this process is revealed. Also, the effects of wall cooling to the receptivity process using slow and fast mode acoustic disturbances are studied. The effects of cooling on the first and second mode regions are investigated. It is found that the first mode is stabilized and the second mode is destabilized by wall cooling when the flow is forced by acoustic waves in the slow mode.