Linear disturbances in hypersonic, chemically reacting shock layers
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The effects of equilibrium- and nonequilibrium-air chemical reactions on the linear stability of a Mach 25,10-deg half-angle sharp-cone shock layer are investigated. First, the basic state is computed using the parabolized Navier-Stokes equations with a shock-fitting scheme. This eliminates spurious numerical oscillations that could adversely affect the stability analysis. Spatial stability analyses are then described for three different approximations of the physics: perfect gas, air in local chemical equilibrium, and air in chemical nonequilibrium. It is shown in both the equilibrium- and nonequilibrium-air calculations that the second mode of Mack is shifted to lower frequencies. This is attributed to the increase in the size of the region of relative supersonic flow due to the lower speeds of sound in the relatively cooler boundary layers. Finally, in the equilibrium air calculations, modes that travel supersonically relative to the in viscid region of the shock layer are shown to exist. These modes are a superposition of incoming and outgoing disturbances whose magnitude oscillates with the distance normal to the wall in the inviscid region of the shock layer. This oscillatory behavior is possible only because the shock standoff distance is finite. 1994 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.
