A reliable PIV approach for measuring velocity profiles of highly sheared granular flows

This work reports a particle image velocimetry (PIV) approach for measuring flow velocities profiles in dry granular flows. An experimental research has been performed on steady-state dry granular flows, reproduced in a laboratory environment and under controlled conditions. Side wall images of the flowing pile have been acquired by a high-speed camera. An open-source code, PIVlab, is employed for the derivation of the velocities profiles from digital images. The reliability of the PIV code has been confirmed by comparing its numerical results with those obtained through using the widely used commercial code, proVISION-XS by IDT Corp. The PIVlab code is found to provide reliable results also in case of high sheared flows, typically observed in the presence of no-slip bottom boundary conditions, thanks to its multi-grid multi-step features, that enhance the dynamic range of velocity measurements and, at the same time, provide a higher spatial resolution.