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Accueil > Équipes > Équipe MEIGE > Diffusion scientifique > Séminaires internes

Mixing in density currents flowing up a slope

07/05/2015 Claudia Adduce (Univ. Roma3)

The dynamics of unsteady gravity currents propagating up a slope are investigated by laboratory experiments and Large Eddy Simulations (LES), focusing on mixing processes between the dense current and the surrounding fluid. Small up-sloping angles of the bottom boundary are considered. The aspect ratio of the initial volume of the dense lock fluid, R, and the inclination of the bottom boundary, θ, are varied. A good agreement is found between laboratory measurements and results from numerical simulations. Different flow regimes were observed : a slumping phase followed by an inertial phase and an eventual viscous phase. Kelvin-Helmholtz instabilities and lobe-and-cleft structures are observed in all the simulated cases. Density and velocity fields obtained by LES show the presence of a reversed flow close to the bottom of the domain which causes an accumulation of dense fluid in the lock region of the tank. Mixing processes occurring between the dense and the ambient fluids are analyzed according to different approaches. The dependence of mixing on all the parameters here varied was highlighted. In particular, a decrease of mixing with the increase of the steepness of the bottom was observed, and an increase of the entrainment processes was detected for small values of R. In addition at the beginning of the process, mixing was found to depend on the development of Kelvin-Helmholtz billows. When these structures lose their coherence, three-dimensional features of the flow appear more evident and produce mixing.