A numerical study of the effect of bed slope angle on the structure of gravity currents propagating over an incline

Large Eddy Simulations (LES) are conducted to understand the changes in the structure of lock exchange bottom propagating currents with the bed slope angle, for currents entering a reservoir with a flat free surface and an inclined bottom. LES accurately predicts the general shape of the current and the temporal evolution of the front position for the 10.6 degrees bed slope angle case. The simulation conducted with a 40 degrees bed slope angle shows that for large angles the structure of the head region is very different from the one observed for very low bed slope angles. For high bed slope angles, a high-circulation Intensified Mixed Vortex (IMV) forms at the back of the head of the current, a short time after the flow is initiated. The head progressively loses its buoyancy to the IMV. For large bed slope angles, after the initial stages of current propagation, the IMV has a much larger capacity to entrain sediment than the head. In both cases, the flow becomes strongly supercritical beneath the IMV, once the coherence of the IMV is sufficiently strong to accelerate the fluid beneath it. This happens much earlier in the high bed slope case. Simulation results also show that the rate of increase of the volume of mixed fluid increases with the bed slope angle.