Towards High-Speed And High-Resolution Real-Time Optical Flow Particle Image Velocimetry

One of the major advantages of Optical Flow PIV (Particle Image Velocimetry) algorithms over Cross-Correlation PIV is their scalability leading to potentially very high computational speeds. This is confirmed in this study using different GPUs (Graphics Processor Unit) and different image sizes. The other advantage is the possibility of obtaining dense velocity fields of up to one vector per pixel. It is well known that particle seeding plays a crucial role in the results of standard particle image velocimetry based on cross-correlation algorithms. Its influence on the quality of the optical flow algorithm is not as well established. In this article the influence of particle concentration is quantified by introducing a criterion considering the proportion of “active” pixels in a snapshot. It is shown that it is possible to optimize particle concentration to maximize the percentage of active pixels, leading to better spatial resolution, down to one vector per pixel. The principle is validated on a vortex-free flow and applied to the complex 3D flow downstream a backward-facing step.