A method to anchor displacement vectors to reduce uncertainty and improve particle image velocimetry results

• Published in: Measurement science & technology Vol. 15; no. 1; pp. 9 - 20
• Main Authors: Young, C N, Johnson, D A, Weckman, E J
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.01.2004
• ISSN: 0957-0233; 1361-6501
• DOI: 10.1088/0957-0233/15/1/002

When large fields of view are used with particle image velocimetry (PIV) in the study of complex fluid flows, extraneous effects linked to velocity gradients and non-uniformities in both image illumination and particle number density become more prevalent. These factors, coupled with the limiting requirement that large areas of interest (AOIs) must be employed to measure the full range of velocity, cause degradation of correlation results (i.e. broadening and/or splintering of the cross-correlation peaks). Advanced iterative and hierarchical PIV strategies provide improved results but these can break down in complex flows where velocity gradients are significant and particle dispersion does not remain uniformly random. One reason for this breakdown is that local displacement vectors obtained using the cross correlation method are not necessarily representative of the fluid motion where these vectors are typically anchored (namely, the geometric centre of the AOI). To address this issue a simple but effective technique is presented that enables individual displacement vectors to be anchored within an AOI at a location(s) where the actual fluid motion is more consistent with the measured displacement. The method involves a straightforward approach to extract the intensity features from within each AOI that most influence the calculation of the cross-correlation plane. To demonstrate the utility of the methodology, bounds of uncertainty are approximated, and results obtained from the analysis of high gradient synthetic flow fields are compared against results obtained using the conventional PIV approach.