The flow field around a hemispherical nose with a sonic opposing jet in a free stream of Mach 2.5 is computed by a time-accurate algorithm using the axisymmetric Navier-Stokes equations. Five total pressure ratios of a jet to a free stream, 0.816 approx 1.633 are examined. The results obtained strongly depend on the toal pressure ratio as the previous experimental results do. In some cases, the computed flow field oscillates intensely where the remarkable change of the jet structure and the surrounding pressure exist. Then it changes from the stable flow to the unstable flow for the same total pressure ratio as in the experiment. The mechanism of the oscillations and the condition of transition between both types of flow are interpreted physically on the basis of unsteady numerical solutions here.
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