APPLICATION OF IMAGE OVERLAPPING TECHNIQUE TO MULTI-PLANE VELOCITY MEASUREMENTS OF FLOWS IN A POROUS-LIKE CHANNEL

摘要

In large field-of-view measurements of micro-particle image velocimetry (micro-PIV), the depth of correlation (DOC) will influence the accuracy of the velocity measurements. The image overlapping technique can effectively decrease the DOC and improve the measurement accuracy of micro-PIV. In this study, the particle image overlapping technique is applied to multi-plane 2D velocity measurements of flows in a porous-like channel with a micro-cylinder array. The influences of additional displacement of the background particle images on the correlation peak displacement are studied using synthetic particle images. The simulation results indicate that correlation peak displacement exists if the number of focal plane particles satisfies certain conditions. Reducing DOC by removing the background particle images decreases the effect of the background particle images on the correlation peak displacement difference. Using the image overlapping technique, the velocity measurement accuracy was improved by background image removal, intensity threshold filtering, and image amplification to decrease the DOC. The 2D velocities on multi-fluid planes and the spatial averaged velocities estimated by the image overlapping technique are compared to those estimated by the correlation averaging technique. The results indicate that the velocity fields can reduce the measurement slip velocity and increase the peak velocity using the image overlapping technique.