Size effects in underwater granular collapses: Experiments and coupled lattice Boltzmann and discrete element method simulations

We perform experiments and simulations of underwater granular column collapses and report an enhanced granular flow mobility as the column size increases. The size effect is attributed to several mechanisms due to the complex fluid-particle interactions. Strong fluid eddies in large cases penetrate through the flowing layer of the granular phase and tend to mobilize more particles disproportionally. The interstitial water lubricates interparticle contacts, causing enhanced basal slip of the fast-moving granular front. This contact lubrication or resistance reduction becomes more prominent in large underwater granular column collapses.