超声速混合层MHz级超高频流动可视化实验

研究发展了超高频基于纳米示踪的平面激光散射（nano-tracer planar laser scattering，NPLS）技术。基于多腔并联脉冲激光器技术、棱锥分光与短曝光相机集成技术以及高精度同步控制技术，实现了MHz级流场可视化和精细测量。采用超高频NPLS技术研究了对流Mach数Ma_c=0.17，0.26混合层流场，获得了时间序列的混合层高分辨率NPLS图像。采用阵列型涡流发生器开展流动控制研究，分析涡流发生器对混合层发展的影响特性。通过选取典型涡结构，分析了超声速混合层不同发展阶段的涡运动和发展演化规律。发现混合层中段的不稳定性发展阶段，涡结构以平移和旋转为主，伴随一定的拉伸；混合层后段以变形和破碎为主，有大量小尺度结构产生。并且小尺度结构会受到剪切、大尺度结构以及小激波的影响，发生明显的非定常运动。 

Experiment on Flow Visualization of Supersonic Mixing Layer at MHz-Level Superhigh Frequency

A superhigh frequency nano-tracer planar laser scattering (NPLS) technique has been developed. Based on multi-cavity parallel pulsed laser technology, beam splitting and short-exposure camera integration technology, and high-precision synchronous control technology, MHz-level flow field visualization was realized. The supersonic mixing layer with convective Mach numbers Ma_c=0.17, 0.26 was studied by superhigh frequency NPLS technology. The flow control research was carried out by using the vortex generator array, and a sequence of high-resolution NPLS images of the mixing layer was obtained. The vortex motion and evolution law of the supersonic mixing layer at different stages were analyzed by selecting typical vortex structures. In the instability development stage of the mixing layer, the vortex structure is dominated by translation and rotation, accompanied by stretching; the later section of the mixing layer is dominated by deformation and fragmentation, and a large number of small-scale vortex structures are generated. In addition, small-scale structures will be induced by sheareffects, large-scale structures, and small shock waves, resulting in obvious unsteady motions.