Numerical study of the vorticity generation behind a sphere descending in a density-stratified fluid

Abstract

Numerical simulation is performed of the flow around a sphere descending in a vertically stratified fluid. We focused here on the axisymmetric flow under relatively strong stratification, and found that a vorticity region is periodically discharged from the sphere, with a sign opposite to the usual vortex discharged in the fluid of uniform density. A Lagrangian analysis along the movement of a fluid particle shows that such a vorticity is generated baroclinically, by the horizontal density gradient across the nearly vertical isopycnal surface.