Study on the Compressible Turbulence Produced by the Interaction of a Laser Induced Shock Wave and Strong Vortex Ring with a Body

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The present studies are concerned with laser-induced breakdown phenomena, and with the interactions between a high-speed vortex ring and a small rigid body. The aims of these studies are to observe the shock waves and the plasma state formed by focusing a pulsed Nd-YAG laser (450 mJ/pulse) in atmosphere, and to prove the effect on the separation of the boundary layer and the flow field induced around a body caused by the shape of a body. The brief conclusion for the results of the experiments by shadowgraph technique are as follows.1)A strong shock wave generated by focusing a laser propagates spherically around the plasma produced. Weak shock waves are generated inside the spherical shock wave, and catch up with the outer spherical shock wave.2)The plasma state is made up of several layers of vortices shaped like a circular disc with the axis in the direction of the laser beam. The spaces between each layer are high pressure, and oblique shocklets go out from the edges of these discs. The plasma plume is emitted in the direction of the incident laser. The plasma occasionally goes into explosion which produces strong shock waves. The plasma is split in half, or a fragment of the breakup plasma comes apart the main and flies away. The outer spherical shock wave is influenced sharply by it.3)As a circular vortex ring approaches a small body, a boundary layer is induced on the side face of the body. In a sharp edge body, an array of small vortices is formed between the edge of the body and the wall vortex core. In a blunt body, an inward-facing shocklet is formed near the separation point. The differences in these flow fields are caused by the velocity of the flow between the body and the vortex ring at the time that the separation bubble is induced.