Physical modeling of the dam-break flow of sedimenting suspensions

Laurence Girolami (1) , Frédéric Risso (2)

1 GéHCO EA6293 - GéoHydrosystèmes COntinentaux
2 IMFT - Institut de mécanique des fluides de Toulouse

We develop a physical model of the dam-break flow of fine non-cohesive particles initially fluidized by a gas. By revisiting previous experiments, we show that the dynamics of such flows involves two uncoupled phenomena. On the one hand, the settling of the particles is the same as that of a non-flowing suspension, so that the mass flux of particles that deposit can be related solely to the properties of the suspension. On the other hand, the flow of the gas-particle mixture is similar to that of an equivalent fluid of constant density and negligible viscosity. The momentum lost by the flowing mixture is equal to the product of the deposited mass flux and the longitudinal velocity. These properties allow us to model the time duration of the flow as the time taken by the particles to settle and the slope of the final deposit as the ratio between the growth rate of the deposit height and the velocity of the front of the dam-break flow. Finally, these findings lead to the formulation of consistent shallow-water equations involving specific terms of mass and momentum transfer at the bottom wall, which can be used to compute the dense lower layer of ash flows generated by a volcanic eruption. They also provide tools for the interpretation of field measurements by geologists.

Mots clés: Suspensions; Sedimentation; Dam-break

Domaines: Mécanique des fluides [physics.class-ph]

Laurence Girolami, Frédéric Risso. Physical modeling of the dam-break flow of sedimenting suspensions. Physical Review Fluids, 2020, 5 (8), pp.084306. ⟨10.1103/PhysRevFluids.5.084306⟩. ⟨hal-02965903⟩