Stereoscopic PIV using optical flow: application to a cavity recirculation

Open cavity flows are a class of wall-bounded flows marked by a recirculation vortex, large velocity gradients, and internal three-dimensional (3D) features. That complex structure results in the combination of an upper shear layer, which can develop a Kelvin–Helmholtz-like instability interacting with walls, the flow injection inside the cavity, the recirculation vortex development, and, for some geometries and Reynolds numbers, a centrifugal Taylor–Görtler-like instability. In order to explore this flow, experimental measurements of the three components of velocity are addressed with stereoscopic two-dimensional particle image velocimetry (3C-2D PIV) using an optical flow algorithm. This technique is a valuable diagnostic tool for quantitative instantaneous description of 3D flows, as those dominated by vortex motion. PIV camera calibration is based on a pinhole model using a single target and camera focal length. The challenging issue is that the studied flow is wall-bounded and subject to laser reflections, which can alter the quality of particle images. A treatment of recorded frames is addressed to get the correct velocity field. PIV measurements are carried out in two orthogonal planes to catch the flow structure and vortex dynamics. Time development of Taylor–Görtler-like vortices is also confronted to the results obtained in previous studies.