A novel approach is devised for the quantification of the systematic uncertainty due to peak locking in particle image velocimetry (PIV), which also leads to correction of the peak-locking errors. The approach relies on a linear regression of the measured displacements from multiple Δt acquisitions (Δt being the time separation between two frames of an image pair). In presence of peak locking, the measured particle image displacement is not a linear function of Δt as the measurement error varies non-linearly with the sub-pixel particle image displacement. In the proposed approach, image acquisition is conducted with multiple Δt’s, and then a linear regression is carried out among the measured time-averaged displacements at different Δt’s, yielding a regression displacement. When the Δt’s are selected properly, the latter represents a correction to the measured displacement where systematic errors due to peak locking are significantly diminished. The expression of the standard uncertainty in the regression displacement is provided. The regression displacement (and velocity) can also be used to quantify the systematic uncertainty due to peak locking in the measured time-averaged displacements (and velocities). The methodology is first assessed with synthetic data and then applied to planar PIV experiments on a uniform flow and an airfoil wake flow. Reference measurements with much larger Δt than the Δt’s of the actual measurements (such that relative peak-locking errors are negligible for the former) are used to validate the proposed approach in both the experiments. Uncertainty coverages for the estimated uncertainties in the velocities measured in the experiments of the uniform flow and the wake flow are of 67% and 59%, respectively, which are comparable to 68% confidence level at which the uncertainties are computed. This proves the validity of the proposed multi-Δt approach for peak-locking uncertainty quantification.
|Title of host publication||Proceedings of the 13th International Symposium on Particle Image Velocimetry|
|Subtitle of host publication||22-27 July, Munich, Germany|
|Editors||Christian J. Kähler, Rainer Hain, Sven Scharnowski, Thomas Fuchs|
|Publisher||Universitat der Bundeswehr Munchen|
|Number of pages||12|
|Publication status||Published - 2019|
|Event||13th International Symposium on Particle Image Velocimetry - Munchen, Germany|
Duration: 22 Jul 2019 → 24 Jul 2019
Conference number: 13
|Conference||13th International Symposium on Particle Image Velocimetry|
|Abbreviated title||ISPIV 2019|
|Period||22/07/19 → 24/07/19|
Figures created during the work on "Multi-Δt approach for peak-locking error correction and uncertainty quantification in PIV"
MATLAB scripts created during the work on "Multi-Δt approach for peak-locking error correction and uncertainty quantification in PIV"