RapidPIV: Full Flow-Field kHz PIV for Real-Time Display and Control

We present a novel architecture for accelerating PIV calculations. An optical flow hardware accelerator does the brunt of the work, with cross-correlation only providing quick corrections. The result is RapidPIV: a free-to-download software program for real-time particle image velocimetry (PIV) for Linux and Windows computers with an Nvidia Turing-gen (or newer) GPU{RapidPIV download at {https://rapidpiv.caltech.edu}{https://rapidpiv.caltech.edu}}. Dense vector and vorticity fields can be displayed in real time when connected to compatible camera. Processing pre-existing PIV image files is also supported. We achieve 1,150 frames-per-second on 1 megapixel images, which is almost 700 times faster than trusted multi-grid software on the same desktop. Accuracy, precision, and robustness are tested with synthetic particle image experiments, and physical experiments involving an accelerated flat plate and a cylinder wake. RapidPIV's accuracy, precision and ability to handle high displacement, velocity gradients, and low seeding density compare favorably with the trusted multi-grid correlation software, agreeing within the noise floor almost everywhere in experiments and performing mostly within a factor of 3 in sub-pixel bias and precision in synthetic tests. For low to moderate loss of particle pairs, or low to moderate noise, synthetic tests show RapidPIV behaves similarly to the multi-grid software even though the multi-grid technique is better suited at high pair losses or noise levels.