Avalanche of fluid in the laboratory: the dam-break problem revisited.

The talk reviews some of the analytical results available for studying the dambreak problem. Emphasis is then given to a thorough comparison between experimental data, analytical results (lubrication theory), and numerical simulations (obtained using the shallow "water" equations) for Newtonian fluids, viscoplastic materials, and density-matched particle suspensions. We show that the front has a specific behavior, due to a large extent to the pronounced curvature of the free surface that causes the shear stress to significantly increase (relative to the behavior in the body), but surprisingly enough, the details of this front behavior are not essential to determining the flow behavior of the fluid avalanche. The last part of the talk is devoted to avalanches of particle suspensions, whose behavior is highly dependent on the particle concentration. In spite of particle migration (which causes a significant blunting of the velocity profile), the analogy with an equivalent homogeneous Newtonian fluid performs well for concentrations as large as 0.56, but for concentrations in excess of 0.58, a more complicated behavior including stick-slip motion is observed.