Numerical study of oscillation mechanism in underexpanded jet impinging on plate

The mechanism of the oscillatory phenomena of an underexpanded jet impinging on a flat plate is studied numerically. Pressure changes generated in the flow field near the plate propagate radially in the surrounding region of the jet. The configuration of the jet boundary is changed by them and so, the waves forming the underexpanded jet are displaced when they are reflected from the jet boundary. And then, the pressure disturbances return to the region near the plate. Unsteady flow with repetition of growth and decay of the separation bubble on the plate is also found under certain conditions.