Analysis of the flow in gravity currents propagating up a slope. (July 2017) - Ottolenghi, L.
Highlights: Large Eddy Simulations of gravity currents flowing up a slope are presented. The presence of a backward flow in the near-wall region is detected and analysed. The potential sediment transport is found to be dependent on the bed upslope. Elongated turbulent structures are observed to develop in the near-wall region. The turbulent kinetic energy decreases as the upslope increases. Abstract: Lock-release gravity currents flowing up a slope are investigated by Large Eddy Simulations. The angle between the bottom boundary and the horizontal direction, θ, and the aspect ratio of the initial volume of dense fluid in the lock, R, are varied. The mean flow is analysed and both density and velocity fields reveal the presence of a backward flow close to the bottom of the domain directed to the lock region. The intensity of the backward flow is discussed in terms of both streamwise velocity component and negative flow discharge. The analysis of the friction velocity at the bottom is also presented, showing the role of the tail region of gravity currents propagating up a slope in sediment transport. Turbulent structures developing in the near-wall region and the budget of the turbulent kinetic energy are analysed in order to investigate the regions of the gravity current in which turbulence is more pronounced. The analysis shows that at the beginning of the process, turbulent quantities have a stronger intensity especially in the areas where Kelvin–Helmholtz billows develop. When these structures lose their coherence, three-dimensional features of the flow appear more evident and the turbulence intensity decreases, still remaining active in the head of the gravity current, at the interface between the two fluids.