Regressive cross-correlation of pressure signals in the region of stenosis: Insights from particle image velocimetry experimentation

Abstract A hybrid method for particle image velocimetry (PIV) is developed to overcome the limitations of the optical flow method applied to PIV images with large displacements. The main elements of the hybrid method include a cross-correlation scheme for initial estimation, a shifting scheme for generating a shifted image, and an optical flow scheme for obtaining a refined high-resolution velocity field. In addition, a preprocessing scheme is used for correcting the illumination intensity change. The accuracy of the hybrid method is evaluated through simulations in a parametric space in comparison with the typical correlation methods and optical flow method. Further quantitative comparisons are made in PIV measurements in a circular air jet.

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An improved cross-correlation method for (digital) particle image velocimetry

Acta Mechanica Sinica ◽

10.1007/bf02487460 ◽

2001 ◽

Vol 17 (4) ◽

pp. 332-339 ◽

Cited By ~ 5

Author(s):

Weng Wenguo ◽

Fan Weicheng ◽

Liao Guangxuan ◽

Qin Jun

Keyword(s):

Particle Image Velocimetry ◽

Cross Correlation ◽

Particle Image ◽

Correlation Method ◽

Digital Particle Image Velocimetry ◽

Image Velocimetry

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Uncertainty Estimation for Ensemble Particle Image Velocimetry

14th International Symposium on Particle Image Velocimetry ◽

10.18409/ispiv.v1i1.143 ◽

2021 ◽

Vol 1 (1) ◽

Author(s):

Adib Ahmadzadegan ◽

Sayantan Bhattacharya ◽

Arezoo M. Ardekani ◽

Pavlos P. Vlachos

Keyword(s):

Particle Image Velocimetry ◽

Uncertainty Quantification ◽

Velocity Gradient ◽

Cross Correlation ◽

Particle Image ◽

Indirect Methods ◽

Error Sources ◽

Piv Measurement ◽

Image Velocimetry ◽

Non Gaussian

We present a novel approach to estimate the uncertainty in ensemble particle image velocimetry (PIV) measurements. Ensemble PIV is widely used when the cross-correlation signal-to-noise ratio (SNR) is insufficient to perform a reliable instantaneous velocity measurement. Despite the utility of ensemble PIV, uncertainty quantification for this type of measurement has not been studied. The existing uncertainty quantification algorithms for PIV are developed and used only for instantaneous PIV measurement and do not account for the improved SNR in ensemble PIV. Existing instantaneous uncertainty quantification methods can be divided into direct and indirect categories. Indirect methods require calibration based on the effect of various image parameters (such as noise, particle size, density, velocity gradient, etc.) on the correlation SNR. Indirect methods have not been calibrated for error sources relevant in an Ensemble PIV measurement. Also, they have lower sensitivity to the error sources compared to direct approaches. Direct methods, such as the moment of correlation (MC) and Image Matching (IM), find the uncertainty based on the images and correlation planes without any calibration and are more reliable (Bhattacharya et al., 2018; Sciacchitano et al., 2013). Ensemble PIV is based on ensemble correlations; therefore, MC, which uses the generalized cross-correlation (GCC) plane as a measure of uncertainty, is the most suitable method to be modified to be applicable for the ensemble PIV. The GCC plane is the inverse Fourier transform of the phase correlation and represents the probability density function (PDF) of particles’ displacements (Bhattacharya et al., 2018; Eckstein and Vlachos, 2009). We replaced instantaneous GCC with ensemble GCC and modified MC’s normalization factor to account for the number of ensembles. The MC’s primary limitation is that it assumes a Gaussian shape for the PDF of displacements and estimate the standard deviation of the underlying PDF using a fitted Gaussian. However, the PDF deviates from Gaussian distribution due to velocity gradient or non-Gaussian random displacements. Therefore, MC’s reliability and applicability are reduced for flow fields with non-Gaussian PDFs. Also, our analysis shows that ensemble MC consistently underestimates the uncertainty. So, a generalized and reliable method for uncertainty quantification for ensemble PIV is needed.

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