Gravity currents from moving sources. (English) Zbl 1480.76029

Ouillon, Raphael; Kakoutas, Christos; Meiburg, Eckart; Peacock, Thomas

J. Fluid Mech. 924, Paper No. A43, 25 p. (2021).

Summary: Emerging technologies such as deep-sea mining and geoengineering pose fundamentally new questions regarding the dynamics of gravity currents. Such activities can continuously release dense sediment plumes from moving locations, thereafter propagating as gravity currents. Here, we present the results of idealized numerical simulations of this novel configuration, and investigate the propagation of a gravity current that results from a moving source of buoyancy, as a function of the ratio of source speed to buoyancy velocity. We show that above a certain value of this ratio, the flow enters a supercritical regime in which the source moves more rapidly than the generated current, resulting in a statistically steady state in the reference frame of the moving source. Once in the supercritical regime, the current goes through a second transition beyond which fluid in the head of the current moves approximately in the direction normal to the direction of motion of the source, and the time evolution of the front in the lateral direction is well described by an equivalent constant volume lock-release gravity current. We use our findings to gain insight into the propagation of sediment plumes released by deep-sea mining collector vehicles, and present proof-of-concept tow-tank laboratory experiments of a model deep-sea mining collector discharging dense dyed fluid in its wake. The experiments reveal the formation a wedge-shaped gravity current front which narrows as the ratio of collector-to-buoyancy velocity increases. The time-averaged front position shows good agreement with the results of the numerical model in the supercritical regime.

MSC:

76D05	Navier-Stokes equations for incompressible viscous fluids
76D50	Stratification effects in viscous fluids
76M20	Finite difference methods applied to problems in fluid mechanics
86A05	Hydrology, hydrography, oceanography

Keywords:

stratified gravity current; Navier-Stokes equations; finite difference method; constant flux regime; supercritical regime; lock-release gravity current; sediment plume propagation

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