Cross-validation of 3D particle tracking velocimetry for the study of granular flows down rotating chutes

Three-dimensional particle tracking velocimetry (3D-PTV) is a promising technique to study the behavior of granular flows. The aim of this paper is to cross-validate 3D-PTV against independent or more established techniques, such as particle image velocimetry (PIV), electronic ultrasonic sensor measurements for bed height, and the discrete element model (DEM), for the complicating circumstance in which granular particles are flowing down a rotating chute. 3D-PTV was used to gain access to Lagrangian trajectory data of surface particles in such flows, from which independent measurements of both the surface velocity and the bed height in the chute were derived. The 3D-PTV method was based on imaging and tracking colored tracer particles that were introduced in the granular material, which are viewed from three directions. The three cameras collected consecutive frames a known time interval apart and the PTV algorithm for locating and tracking particles was used to determine particle trajectories and velocities. We found that the 3D-PTV results are in good agreement with PIV results with regard to the streamwise and spanwise surface velocity of particles in the rotating chute. The particle bed height obtained from 3D-PTV was also found to be in good agreement with data from an ultrasonic bed-height sensor. The experimental findings from PTV for the non-rotating case were used to tune the friction coefficient in our DEM simulations. The simulation method was validated by the good agreement between experimental findings and simulations at all rotation rates studied