Three-dimensional Vorono? imaging methods for the simultaneous measurement of velocities and concentrations in dense particulate flows

摘要

A set of recently developed stereo imaging algorithms are proposed for the combinedrnexperimental characterization of 3D velocities and concentrations in dense particulate flows,rnimaged by twin cameras through a transparent plane. A robust 3D-PTV algorithm isrndescribed. An estimate of volumetric concentration is proposed, based on the surface densityrnof near-wall particles, and calibrated on a set of Monte-Carlo simulations. The originality ofrnthe methods lies in exploiting the properties of the Vorono? diagram to perform in a robust andrnefficient way the various steps of the analysis: stereoscopic matching, volumetric samplingrnand particle-tracking operations. In contradiction with traditional methods for particletrackingrnand concentration estimation, the present methods have proven to be successful evenrnin case of highly concentrated, rapidly sheared dispersions of many identical particles. Theyrncan handle occlusion effects, which intervene for dense dispersions and corrupt concentrationrnestimates. The methods are applied and validated on a set of fluidization cell experiments,rnallowing the derivation of full sets of 3D granular trajectories and estimates of thernhomogeneous concentration within the fluidized bed.