脉冲激光等离子体与正激波相互作用的PIV实验研究

脉冲激光等离子体与超声速流场相互作用在飞行器减阻隔热、点火助燃等方面具有重要的应用价值.纹影实验方法只能定性或半定量地反映流动状态.为定量研究速度分布和旋涡结构,针对激光等离子体及其与正激波相互作用过程开展粒子图像测速PIV实验研究.在激波管实验平台上建立了纳秒脉冲激光能量沉积系统和PIV测量系统,通过定量测量,探明了激光等离子体引致的激光空气泡以及热核的流动特性,揭示了激光等离子体在正激波冲击下的流动特性与演化规律,并给出了激光能量大小和位置对相互作用过程的影响.结果表明:激光空气泡内的速度分布在激光入射方向上并不关于击穿点对称,而是在靠近激光入射方向一侧的流速略大于远离激光入射方向一侧;斜压导致热核在演化初期产生涡环,后期则由剪切主导;正激波与激光空气泡界面、热核界面相互作用时,产生斜压涡量,当激光能量为87.8 mJ、正激波马赫数1.4时,热核在正激波作用下产生的涡量比在静止空气中演化时大1个数量级;激光与正激波相互作用的关键过程是热核在正激波冲击下演化成涡环,在激波波前注入激光能量能够获得更加显著的涡环.

PIV EXPERIMENT STUDY ON INTERACTION BETWEEN PULSED LASER PLASMA AND NORMAL SHOCK

The interaction between pulsed laser plasma and supersonic flow field has important application value on aircraft drag reduction and heat insulation, ignition and combustion assistance. In order to quantitatively study the velocity field and vortex structure, particle image velocimetry (PIV) experiments were carried out on laser plasma and its interaction with normal shock wave. The nanosecond pulse laser energy deposition system and PIV measurement system were established on the shock tube experimental platform. By quantitatively measuring, the flow characteristics of laser air bubbles and hot core induced by laser plasma are explored. The flow characteristics and evolution of laser plasma under the impact of normal shock waves are revealed, and the influence of laser energy magnitude and deposition position on the interaction process is given. The results show that the velocity distribution in the laser air bubble is not symmetrical about the breakdown point in the laser incidence direction, but the flow velocity near the laser incidence direction is slightly larger than that far from the laser incidence direction. The baroclinic pressure leads to the generation of vortex rings in the early stage of hot core evolution, and the later stage is dominated by shearing force. When the normal shock interacts with the laser air bubble interface and the hot core interface, the baroclinic vorticity is generated. When the laser energy is 87.8 mJ and the normal shock Mach number is 1.41, the vorticity generated at the hot core interface is one order of magnitude larger than that in the static air. The key process of the interaction between the laser and the normal shock wave is that the hot core evolves into a vortex ring under the impact of the normal shock wave. The deposition of laser energy in front of the shock wave can obtain a more significant vortex ring.