Buoyancy induced mobility in two-phase debris flow

Abstract

This paper shows that buoyancy enhances mobility in two-phase debris flow with an analysis based on the generalized two-phase debris flow model proposed by Pudasaini [1]. The model (the most generalized two-phase flow model to date) incorporates many essential physical phenomena, including solid-volume-fraction-gradient-enhanced non-Newtonian viscous stress, buoyancy, virtual mass and a generalized drag force. We find a strong coupling between the solid- and the fluid-momentum transfer, where the solid normal stress is reduced by buoyancy, which in turn diminishes the frictional resistance, enhances the pressure gradient, and reduces the drag on the solid component. This leads to higher flow mobility. Numerical results show that the model can adequately describe the dynamics of buoyancy induced mobility in two-phase debris flows, and produces observable geometry of flowing mass in the run-out zone. The results presented here are consistent with the physics of the flow.