High-resolution simulations of particle-driven gravity currents

Abstract High-resolution simulations are presented of particle-driven gravity currents in the lock-exchange configuration. The study concentrates on dilute flows with small density differences between particle-laden and clear fluid. Moreover, particles are considered which have negligible inertia, and which are much smaller than the smallest length scales of the buoyancy-induced fluid motion. For the mathematical description of the particulate phase a Eulerian approach is employed with a transport equation for the local particle-number density. The governing equations are integrated numerically with a high-order mixed spectral/spectral-element technique. In the analysis of the results, special emphasis is placed on the sedimentation of particles and the influence of particle settling on the flow dynamics. Time-dependent sedimentation profiles at the channel floor are presented which agree closely with available experimental data. A detailed study is conducted of the balance between the various components of the energy budget of the flow, i.e. the potential and kinetic energy, and the dissipative losses. Furthermore, the simulation results, along with a modified Shields criterion, are used to show that resuspension of sediment back into the particle-driven current is unlikely to occur in the cases considered. Two-dimensional (2D) and three-dimensional (3D) computations are compared which reveal that, for the present configuration, a 2D model can predict reliably the flow development at early times. However, concerning the long-time evolution of the flow, more substantial differences exist between 2D and 3D simulations.