面向高速流场的四棱锥探测方法研究

It is a persist pursuit to find an optical quantitative measurement method with few optical elements to detect both the complex flow field structure and density distribution for high-speed flow field visualization. The widely used schlieren technique in flow field measurement is mostly qualitative. The optical path of Pyramid wavefront sensor is similar to schlieren’s, besides replacing the knife with a pyramid-shape prism. It has the advantage of providing more precise flow field structure and quantitative measurement. Using the refraction effect of pyramid-shape prism, four sub-images can be obtained simultaneously. With which the flow field structure in the orthogonal direction is provided, which is especially suitable for asymmetric flow field detection. Quantitative detection of the flow field can be achieved by using the relationship between the signal and the wavefront slope. To obtain this, the information fusion method of four directions sub-images is studied to provide more abundant flow field structure for high-speed flow field. The method to enlarge linear relationship between signal and wavefront slope should be studied for the quantitative wavefront measurement. The relationship between the wavefront distortion and the high-speed flow field density will be researched to make the quantitative measurement more intuitive. On the basis, experiments in wind tunnel will be carried out to verify the detection range and precision. The research will provide an efficient wavefront detection method, reveal the basic rules of the flow field on a more elaborate level, and promote the development of high-speed flow field testing technology.

寻求一种光路简洁，可对高速流场的复杂结构和密度分布进行测量的光学检测手段是流场显示技术的追求。流场测量中广泛使用的纹影法，多用于定性检测，而四棱锥波前传感器与纹影法光路相似，采用四棱锥镜代替刀口后，可提供更准确的流场结构，还可实现对流场密度的精确测量。利用棱锥的折射作用，保留四个方向的流场信息，可同时实现正交方向流场结构的探测，特别适合非对称流场的检测，再结合信号与波前的关系，实现流场的定量检测。研究四个方向信息融合方法，为高速流场提供更丰富的流场结构；研究信号与波前斜率之间的线性范围扩大的方法，实现波前的定量测量；研究波前与高速流场密度之间的关系，让定量测量更直接。在此基础上，在风洞的高速流场中研究探测范围和精度，从而为高速流场测量提供一种高效的波前检测方法，在更精细的层面上揭示流场的基本规律，推动高速流场测试技术的发展。

随着空气动力学研究及相关工程应用的发展，对定量化测量技术的需求越来越强烈，而基于四棱锥波前传感器的测试技术因光路结构与纹影法类似且探测原理清晰，可以同时获得四个方向的类纹影信号及能够实现定量测量，被引入到流动测量中。本项目，完成了像差的频率域特性分析，对波前传感器校正能力进行分析，为后续自适应光学闭环校正提供理论依据；根据某小型风洞的光学参数，设计核心器件屋脊棱镜，并搭建实验光路，完成了利用液晶空间光调制器作为变形镜的静态像差闭环校正实验，最后在小型风洞内完成了对激波串、常见流场模型的流场测量，得到了清晰且精细的流场结构，捕捉到高速流场边界层的湍流、转捩、层流等结构。本研究，证实了四棱锥波前传感器是一种适合流场探测的新方法。