Effect of resolution on the speed and accuracy of particle image velocimetry interrogation
Effect of resolution on the speed and accuracy of particle image velocimetry interrogation
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DOI：
10.1007/bf00218156
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发表时间：
1992-06
影响因子：
2.4
通讯作者：
Ajay K. Prasad;Ronald J. Adrian;C. Landreth;P. W. Offutt
中科院分区：
文献类型：
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作者：
Ajay K. Prasad;Ronald J. Adrian;C. Landreth;P. W. Offutt
粒子图像测速技术结合了一种过程，通过该过程，流场图像包含了种子粒子的双重图像，在称为“审问点”的小区域中进行分析。每个点成像到光电探测器阵列上，其数字化输出使用自相关技术进行计算评估。本文研究了使用不同分辨率的阵列来解决斑点的影响，主要是为了提高速度。为此，两个特别创建的测试照片代表(i)均匀流动和（ii）实体旋转，使用阵列大小从32 × 32到256 × 256进行查询。分辨率每降低两倍，审讯速度就会提高四倍，但这种好处会被准确性的降低所抵消。颗粒图像直径通过两种不同的误差机制强烈影响精度。当粒子图像与像素相比较小时，由于相关函数的数值分辨率有限，平均偏差误差变得显著。相反，当粒子图像较大时，由于电子图像中的不规则性导致的随机误差占主导地位。因此，最佳图像尺寸不在于任何一个极端，而在于一个中间值，使得粒子图像在绝对意义上很小，但相对于像素尺寸又很大。
Particle image velocimetry incorporates a process by which an image of a flow field, bearing double images of seeding particles, is analyzed in small regions called “interrogation spots.” Each spot is imaged onto a photodetector array whose digitized output is evaluated computationally using the auto-correlation technique. This paper examines the effects of resolving the spot using arrays of various resolutions, motivated primarily by a gain in speed. For this purpose, two specially created test photographs representing (i) uniform flow and (ii) solid body rotation, were interrogated using array sizes ranging from 32 × 32 to 256 × 256. Each reduction in resolution by a factor of two gains a factor of four in interrogation speed, but this benefit is counteracted by a loss in accuracy. The particle image diameter strongly influences accuracy through two distinct error mechanisms. When the particle image is small compared to the pixel size,mean bias errorbecomes significant due to finite numerical resolution of the correlation function. Conversely, when the particle image is large,random errordue to irregularities in the electronic images predominates. The optimum image size, therefore, lies not at either extreme but at an intermediate value such that the particle image is small in an absolute sense, and yet large relative to the pixel size.