Study on Fluid Dynamic Effect of Supersonic Flight over the Ocean on Undersea Environment

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In the environmental problems of the supersonic transport, the influence of the shock wave or sonic-boom on the undersea environment has not been well understood. It is necessary to clarify the characteristics of the underwater pressure field induced by the shock wave traveling over the water surface. In the present study, the propagation of the shock wave in the separated gas-liquid layer is experimentally and numerically investigated.In the experiments, the normal shock wave generated by the shock tube propagates in the separated gas-liquid layer of a horizontal duct with a step of the water tank. Results show that : 1) the propagation of the normal shock wave in the air is hardly affected by the presence of the water, 2) the interaction between the precursor wave and the main wave may cause strong pressure oscillation in the water, and 3) the oscillatory nature of the underwater pressure depends on the acoustic velocity and depth of the water.In the computation, the separated gas-liquid layer is solved in a unified manner by using the CIP-CUP method. Both the shock wave in the air and the oscillatory pressure wave in the water are captured and qualitative agreement with the experiments is obtained. Results show that the boundary condition at the wall and evaluation of the acoustic velocity are quite important in predicting the underwater pressure wave.It is pointed out by the present study that the magnitude of the induced pressure wave in the water may be larger than the pressure jump across the shock wave in the air and that the influence of the supersonic flight over the ocean on the underwater pressure field should be considered in the assessment of the environmental problems of the supersonic transport as well as the sonic-boom at the overland flight.