高速复杂流动结构的视频测量

为了定量显示空腔高速复杂流动结构,采用均布的小圆点作为背景纹影(BOS)的背景点,利用视频测量(VM)成熟的小圆点图像定位与匹配技术,克服了现有图像互相关技术对BOS的限制;推导非平行光穿过流场的偏折位移/角计算公式,基于VM的共线方程,准确计算从背景点到相机摄影中心的光束穿过流场产生的偏折位移场和光程差场(OPD)。FL-21风洞的某空腔高速(马赫数为0.6~2.0)复杂流动结构的视频测量结果表明:本方法可清楚分辨出亚微米量级的光程差差异与微弧度量级的偏折角差异,定量显示空腔高速流动产生的波/涡/剪切层的位置、强弱及其相互关系,为复杂流动结构与气动光学效应的测量与显示提供新的途径,其光路简单、无需价格昂贵的相干光源,具有应用前景。

Videogrammetry measurement for high-speed complex flow structures

To quantify the structures of high-speed flow over a cavity,small circle points with equal space in the row and column are used as background for background oriented schlieren (BOS),and image processing techniques of mark points in videogrammetry measurement (VM) are also employed to break the limits of cross-correlation in existing BOS.The expres sions for computing refraction angle and displacement of nonparallel beams are derived.The fields of optical path difference (OPD) and refraction displacement when the beams from the small circle points to the center of the camera is crossing the flow are accurately calculated based on VM collinear equations.The measuring data on flow over the cavities in FL-21 wind tunnel demonstrates that the OPD differences no more than 1 μm and refraction angle about 1 μrad can be perceived distinctly,and the structures of waves/vortices/shear layer are quantified.The method proposed can provide a new way to measure aero-optic effects and visualize the complex flows.With simple optical system and no expensive coherent sources,the method has great application potential.