Basal entrainment by Newtonian gravity-driven flows

摘要: Gravity-driven flows can erode the bed along which they descend and increase their mass by a factor of 10 or more. This process is called basal entrainment. Although documented field observations laboratory experiments, it remains poorly understood. We look into this issue studying eroding dam-break waves. More specifically we would like to determine what happens when viscous gravity-driven flow generated releasing fixed volume incompressible Newtonian fluid encounters stationary erodible layer (composed with same density viscosity). Models based on depth-averaged momentum balance equations deal bed-flow interfaces as shock In contrast, use an approach involving long-wave approximation Navier-Stokes (lubrication theory), in context, are acceleration waves that move quickly across thin layers. The incoming digs down bed, pushing up downstream material, thus advancing front. Extending method used Huppert [J. Fluid Mech. 121, 43–58 (1982)] for modelling waves, end nonlinear diffusion equation depth, solved numerically. Theory compared experimental results. Excellent agreement found limit low Reynolds numbers (i.e. lower than 20) front position over time depth profile. model has sometimes been describe behaviour natural materials such snow debris suspensions, but majority existing approaches rely more elaborate constitutive equations. So there no direct application results presented here real conditions. Yet, our study sheds light mechanisms involved provide evidence whole loose material entrained once makes contact layer. As occurs very short times, consider underneath mobilized instantaneously.