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

目前的研究涉及激光诱导击穿现象以及高速涡环与小刚体之间的相互作用。这些研究的目的是观察脉冲激光(450mJ/脉冲)在大气中聚焦时形成的激波和等离子体状态，并验证物体形状对边界层分离和物体周围流场分离的影响。用阴影照相法对实验结果作了简要总结：1)激光聚焦产生的强冲击波在产生的等离子体周围球状传播。在球面冲击波内部产生弱激波，并赶上外部球面冲击波。2)等离子体状态是由几层圆盘状的涡旋组成的，其轴向是激光的方向。每一层之间的空间都是高压的，倾斜的冲击波从这些圆盘的边缘出来。等离子体羽流沿着入射激光的方向发射。等离子体偶尔会发生爆炸，产生强烈的冲击波。等离子体被一分为二，或者分裂的等离子体的一部分从主管道分离并飞走。外球激波受其影响很大。3)当圆形涡环靠近小物体时，在物体侧面形成边界层。在尖边形体中，在形体边缘和壁面涡核之间形成一系列小涡流。在钝体中，在分离点附近形成向内的小冲击。这些流场的差异是由分离气泡诱导时物体和涡环之间的流动速度引起的。

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.