粒子拖尾长度对高频DPIV测量误差的影响

Bias error induced by particle tailing in DPIV measurement

基于连续激光源的高采样频率DPIV系统在进行曝光时可能会产生粒子拖尾现象。明渠湍流试验和数值模拟试验结果显示,粒子拖尾长度的增加会导致平均流速减小和湍流强度增大。分析表明,导致平均流速误差的原因之一是诊断窗口边缘局部粒子图像的缺失,且图像缺失程度会随着粒子拖尾长度增加而增大,从而使平均速度随粒子拖尾长度增加而减小;粒子拖尾的另一个直接后果是增大了粒子图像的有效粒径,从而导致湍流强度增大。通过增大第二个诊断窗口的尺寸,进行相关函数标准化和相关系数补偿等方法,可以消除粒子拖尾长度引起的误差。

The presence of particle tailing affects the performance of DPIV systems that use continuous wave laser as light source. Open-channel flow experiments and numerical stimulations show that the measured mean velocity of the flow decreases and the turbulent intensity increases when the exposure time prolongs. Underestimation of the mean velocity is due to the fact that the existence of particle tailing aggravates the partial lost of particle images near the boundary of the interrogation windows. Overestimation of the turbulent intensity is caused by the enlargement of the seeding particles due to particle tailing. An algorithm was proposed to eliminate or reduce these errors by enlargement of the second interrogation window, normalization of correlation function and complementation for integer peak neighbors.