CFD-DEM study on the entrainment induced by debris flows with the HBP rheological model

Abstract

The interaction between basal and earth-surface flows such as dam-break flows, hyper-concentration flows and debris flows, for example, entrainment and erosion, have crucial influences on their dynamic characteristics and rheological behaviour. Among these mass flows, debris flows that are able to entrain a great number of masses tend to be the most catastrophic. A fully coupled CFD-DEM technique is utilised here to evaluate the erosion effect of debris flow on the sand basal, in which basal is modelled via a non-cohesive particle assembly using DEM and debris flows are recognised as a non-Newtonian fluid. Herschel-Bulkley-Papanastasiou (HBP) rheological model is implemented to capture the viscous behaviour of debris flows. Besides, considering the gap-graded feature of basal, the traditional coarse-grain method that accounts for porosity based on particle centres may result in inaccuracy in void fraction determination. Thus, the semi-resolved method is used to determine physical fields. Morphology of the basal is updated each time step following DEM calculation cycles.