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平行光束在变折射率流场中传输时,会偏离其原来的传播方向,同时产生波前畸变.根据Malus定律,若能测得平行光束透过流场后的偏折角,就可得到波前畸变的空间梯度,进而采用波前重构算法计算波前畸变的空间分布.背景导向纹影技术(background oriented schlieren,BOS)的两个特性为测量波前畸变提供了有利条件:BOS技术通过测量参考背景图像和实验背景图像之间的相对位移,可对光束通过流场后的偏折角进行定量测量;在纹影模式的BOS系统中,只有垂直于背景图像的平行光线才能入射到相机,便于研究平面光波透过流场后的波前畸变.有鉴于此,本文基于纹影模式的BOS系统,构建了波前畸变的空间梯度和背景图像位移的定量关系,并选用Southwell波前重构算法,开发了一种测量气动光学波前畸变的新方法——基于BOS的波前测量技术(BOS-based wavefront technique,BOS-WT).本文构建的一套BOS-WT系统,其时间分辨率高达6ns,时间相关分辨率最高可达0.2μs,能够对波前的瞬态分布进行时间相关的定量测量,而且设备简单、易于操作.采用该系统,研究了超声速混合层的气动光学性能,测得了时间间隔5μs的瞬态波前分布;测量结果不仅再现了平面光波通过超声速混合层后波前的瞬态分布,而且对比两个时刻的测量结果,可观察波前随时间的演化规律.
When the parallel beam is transmitted in the variable refractive index flow field, it will deviate from its original propagation direction and produce wavefront distortion.According to Malus’s law, if the deflection angle of the parallel beam through the flow field can be measured, the wavefront Distortion space gradient and then use the wavefront reconstruction algorithm to calculate the spatial distribution of wavefront distortion.Background Two features of background oriented schlieren (BOS) provide favorable conditions for the measurement of wavefront distortion: the BOS technique measures With reference to the relative displacement between the background image and the experimental background image, the deflection angle of the beam after passing through the flow field can be measured quantitatively. In the BOS system of the shadow mode, only the parallel rays perpendicular to the background image can be incident on the camera, The paper studies the wavefront distortion after the planar lightwave passes through the flow field.Therefore, based on the BOS system of the smear mode, the quantitative relationship between the spatial gradient of the wavefront aberration and the background image displacement is constructed, and the wavefront reconstruction algorithm of Southwell , A new method to measure the wavefront distortion of aero-optics has been developed - BOS-based wavefront measurement (BOS-WT) .A set of B OS-WT system with time resolution of up to 6ns and time-dependent resolution of up to 0.2μs enables time-dependent, quantitative measurement of the transient wavefront distribution and is simple and easy to operate. With this system, The results show that the instantaneous wavefront distribution of 5μs time interval is obtained. The measurement results not only reproduce the transient wavefront of the plane wave after passing through the supersonic mixing layer, but also compare the measurement results at two time points Wavefront evolution with time.