Granular collapse in a fluid: Different flow regimes for an initially dense-packing

Laboratory experiments of the granular collapse of an initially dense-packing column in a fluid are reported. By extracting the temporal evolution of the granular material height profile, both the dynamics of the granular flow and the final deposit are characterized depending on the Stokes number St, based on a dissipative process at the grain scale, the grain-fluid density ratio r, and the aspect ratio a of the initial column. A full description of the granular collapse including the transient dynamics of the flow and the characterization of the final shape deposit is proposed. The main contribution of the present study is to provide (i) the St dependence on the granular collapse beyond the effect of the aspect ratio a already reported in previous studies, (ii) the characterization of granular flow regimes in the ((d/Hi)(1/2)St,(d/Hi)(1/2)r) plane, where d/H-i is the particle diameter to initial column height ratio, and (iii) simple correlations to describe the granular collapse which would be of interest for geophysical purposes.