传统流速测量实验技术包括压力皮托管和热线风速仪等侵入式测量技术，在进行超音速测量时侵入式测量会对流场产生显著影响。粒子图像测速（Particle Image Velocimetry, PIV）技术是一种基于激光成像的非侵入二维速度场测试技术，通过图像采集系统记录不同时刻的流场粒子图像，利用互相关算法获得速度场。在超声速流场中应用为保证流场跟随性，需要使用纳米级直径示踪粒子，存在分布不均跟随性差甚至影响反应流场化学反应路径的劣势。纹影成像测速（Schlieren Image Velocimetry, SIV）技术，是一种无示踪粒子的测量技术，以具有显著特征的运动结构作为“示踪粒子”，适用于存在流场相干结构的应用，如大尺度湍流相干结构和湍流边界层等。纹影成像测速技术基于纹影图像亮度的强度变化，亮度强度与流场密度梯度变化相对应；常规纹影光路为光线经过流场测试区域的沿程积分，平面成像获得的是三维流动结构的二维投影，不符合流体力学基本连续性假设，因此，有效的纹影成像测速需要基于二维纹影技术。综上，需要发展基于激光聚焦纹影的流场测速技术，一方面通过纳秒脉宽激光实现超声速流场冻结，另一方面通过聚焦纹影技术实现二维流动显示，并以此为基础发展光流算法，最终实现超声速流场的速度测量

激光聚焦纹影技术近年来获得了系列进展，然而推广应用需要解决光源均匀性和刀口栅制备两个主要难题。由此构成本文的主要创新贡献。针对聚焦纹影光源均匀性问题和刀口栅制备难题，本文提出使用积分球实现了均匀光源；使用光绘菲林技术实现了微米级刀口栅和光源栅的精密制作；搭建了聚焦纹影光路系统，具有光源均匀性好、切光效果精度高的优点。针对聚焦纹影光流算法，本文总结了前人工作，推导了适用聚焦纹影的投影运动光流方程，完善了纹影光流算法，并通过湍流盒初步验证了纹影光流算法的正确性。

The traditional flow measurement techniques including the pitot tubes and hot wire measurements are intrusive which would introduce severe flow interference specially in the application of supersonic flow. Particle Image Velocimetry (PIV) is an non-intrusive laser based velocity measurement technique which relies on two sequential images and correlation algorithms of flow velocity extraction. In order to ensure the response of the tracer particle to the dispersed flow field, the diameters of the tracer particles are selected below 100 nanometers in the application of supersonic flow. This could induce inhomogeneous dispersion and possible distortion to the chemical reaction path. Thus it is desirable to develop a measurement technique without tracer particles. The Schlieren Image Velocimetry (SIV) is a flow velocity measurement technique based on the Schlieren imaging and the optical flow tracking algorithm. The traditional z type Schlieren imaging is an integral over the three dimensional flow path which would violates the continuity assumption of fluid mechanics. Thus the effective application is limited to the two dimensional focusing Schlieren techniques. The combination of the two dimensional focusing Schlieren technique and the optical flow algorithm is essential for the flow velocity measurement based on the SIV.

The focusing Schlieren techniques have been developed over the years. The uniform light source and the manufacture of the cut-off grids at the scale of a few micron meter are two major challenges of this measurement technique. Thus we aim to develop solutions to solve the two issues. The integral sphere is used to generate uniform light source and the image filming method is applied to produce precise cut-off grids. The focusing Schlieren system based on the two improvements has the advantage of high uniformity and cut off precision. Combined with the optical flow algorithm, the developed SIV system has been applied to a homogeneous and isotropic flow field and yields  good results.