Novara Matteo, Scarano Fulvio
Department of Aerospace Engineering, Delft University of Technology, Delft, The Netherlands.
Exp Fluids. 2012;52(4):1027-1041. doi: 10.1007/s00348-011-1187-y. Epub 2011 Sep 4.
The motion tracking enhancement technique (MTE) is a recently introduced method to improve the accuracy of tomographic PIV measurements at seeding density higher than currently practiced. The working principle is based on the fact that the particle field and its projections are correlated between the two exposures. Therefore, information from subsequent exposures can be shared within the tomographic reconstruction process of a single object, which largely reduces the energy lost into . The study follows a previous work based on synthetic particle images, showing that the MTE technique has an effect similar to that of increasing the number of cameras. In the present analysis, MTE is applied to Tomographic PIV data from two time-resolved experiments on turbulent shear flows: a round jet at = 5,000 ( = 1,000 Hz) and a turbulent boundary layer at the trailing edge of an airfoil ( = 370,000) measured at 12,000 Hz. The application of MTE is extended to the case of more than two recordings. The performance is assessed comparing the results from a lowered number of cameras with respect to the full tomographic imaging system. The analysis of the jet flow agrees with the findings of numerical simulations provided the results are taking into account the concept of MTE efficiency based on the volume fraction where - (Elsinga et al. 2010a) are produced. When a large fraction of fluid has uniform motion (stagnant fluid surrounding the jet), only a moderate reduction in is expected by MTE. Nevertheless, a visible recovery of reconstruction quality is observed for the 3-cameras system when MTE is applied making use of 3 recordings. In the turbulent boundary layer, the objective is set to increase the seeding density beyond current practice, and the experiments are performed at approximately 200,000 particles/megapixel. The measurement robustness is monitored with the signal-to-noise ratio S/N for the cross-correlation analysis. An estimate of the precision error is obtained for the turbulent boundary layer case following the peak height of the spatio-temporal cross-correlation function (-). The MTE approach appears to be essential for the increase in robustness and measurement precision at such seeding density.
运动跟踪增强技术（MTE）是最近引入的一种方法，用于在高于当前实践的种子密度下提高层析粒子图像测速（PIV）测量的准确性。其工作原理基于这样一个事实，即粒子场及其投影在两次曝光之间是相关的。因此，来自后续曝光的信息可以在单个物体的层析重建过程中共享，这在很大程度上减少了散失到……中的能量。该研究延续了之前基于合成粒子图像的工作，表明MTE技术具有与增加相机数量类似的效果。在本分析中，MTE应用于来自两个关于湍流剪切流的时间分辨实验的层析PIV数据：一个雷诺数Re = 5000（f = 1000 Hz）的圆形射流，以及一个在12000 Hz下测量的翼型后缘处的湍流边界层（Re = 370000）。MTE的应用扩展到了多于两次记录的情况。通过将相机数量减少后的结果与完整的层析成像系统的结果进行比较来评估性能。射流流动的分析与数值模拟结果一致，前提是在考虑基于产生粒子的体积分数的MTE效率概念的情况下（Elsinga等人，2010a）。当很大一部分流体具有均匀运动（射流周围的停滞流体）时，预计MTE只会使误差有适度降低。然而，当使用3次记录应用MTE时，对于3相机系统观察到了重建质量的明显恢复。在湍流边界层中，目标是将种子密度提高到超出当前实践的水平，实验在大约200000个粒子/兆像素下进行。通过互相关分析的信噪比S/N来监测测量的稳健性。对于湍流边界层情况，根据时空互相关函数（-）的峰值高度获得了精度误差的估计值。MTE方法对于在这种种子密度下提高稳健性和测量精度似乎至关重要。
