光栅纹影偏折法测量二维层化流体密度梯度

Measurement of density gradient for 2D flow field using grating schlieren deflectometry

提出了一种简单的流体密度梯度分布测量系统,该系统在传统纹影系统中引入计量光栅,将光线因流体密度变化引起的偏折转变为投影条纹图的变形,通过分析变形条纹图来提取流体密度梯度分布信息。在分析条纹图时,使用小波变换相位分析法,利用小波变换的局部化特性,有效消除无效数据的影响。实验结果表明:系统的密度梯度测量范围能够达到0.01 g/cm4,测量精度能够达到5×10-6g/cm4。系统装置简单,调节方便,适用于密度变化大的流体密度梯度测量。

A simple density gradient measurement system for 2D flow fields was proposed. The system introduced a grating into the traditional schlieren system and transformed deflection rays caused by density change of a flow field into the deformation of fringe pattern formed by grating projection, so density gradient information of the flow field could be extracted from the deformed fringe pattern. With wavelet location characteristics, a wavelet transform phase demodulation method was applied to fringe pattern analysis to eliminate effect of invalid data effectively. Experimental results indicate that the measuring range of the system can reach 0.01 g/cm^4 and the measurement precision can reach 5×10^-6 g/cm^4 , which shows proposed system is simple in setup,easy in adjustment and suitable for density gradient measurement for flow fields with large density variation.