Direct numerical simulations of Coriolis effects on cylindrical gravity currents
Jeudi 23 juin à 14 h 00 Amphithéâtre Nougaro
Séminaire Mariano I. Cantero
National Commission of Atomic Energy (CNEA), National Council for Scientific and Technological Research (CONICET) and Institute Balseiro, Bariloche Atomic Center (CNEA), San Carlos de Bariloche, Rio Negro, Argentina
Visiting professor at Institut de Mécanique des Fluides de Toulouse (IMFT), Toulouse, France through Scientific Exchange Program SMI 2015 (INPT)
HEGIE research group at IMFT invited seminar.
Gravity currents are flows generated by the action of gravity over fluids with different densities. The modeling of gravity currents at large scales on Earth makes it necessary to account for Coriolis effects owing to rotation, which modify completely the dynamics of the flow. This work addresses Coriolis effects on gravity currents with a cylindrical initial condition by means of direct numerical simulations. The numerical results show an oscillatory behavior of the flow and the existence of a final state where the front acquires a lens shape. These findings are in good agreement with experimental observations. The bottom boundary condition for velocity has an important effect on the flow development. The enhanced viscous shear stresses at the bottom wall for the case of no-slip boundary flows produce a delay of the front as compared to bottom free-slip flows. Interestingly enough, successive fronts reach further away for each oscillation in the case of bottom no-slip flows as opposed to bottom free-slip flows where the maximum distance of propagation is achieved at the first oscillation. In the case of Coriolis-affected gravity currents, the front develops the structure of lobes and clefts even with free-slip bottom boundary conditions. In this case, the structure develops as a consequence of vertical Kelvin-Helmholtz vortices forming at the leading edge of the front. The turbulent structures in the flow are visualized and described in detail. In the absence of Coriolis forces a hairpin vortex can be identified at each front lobe. These hairpin vortices at the front are replaced by vertical Kelvin-Helmholtz vortices in Coriolis-affected currents. It is worth mentioning that the hairpin vortices found at the front lobes in non-rotating currents are not the traditional boundary layer hairpins since they have the opposite rotation sense.