Effects of Density Stratification on an Isolated Vortex in the Process of Decaying

Abstract

Effects of density stratification on the three-dimensional structure of an isolated vortex with the vertical axis in the process of decaying in a non-rotating system are investigated by numerical experiments based on the finite volume solution of the Navier-Stokes equation for inhomogeneous fluid, the continuity equation and the transport equation of density variation. A circular vortex is embedded in stratified fluid with the constant density gradient, and the computation in the time-marching procedure gives the velocity and vorticity distributions, the dissipation of total kinetic energy and the radius of vortex core in the decaying process. The results show that the convergence flow in the bottom boundary layer causes the upwelling flow in the vortex, and both form the vertical circulation in the vortex. When dense fluid on the bottom is raised by the upwelling flow ,the density interface appears in the form of a circular corn between this dense fluid and above stratified fluid, which confines the main part of the vertical circulation below it and weakens the three-dimensional motion of the upper flow. Hence the density stratification reduces the dissipation rate of kinetic energy and it elongates the life of voretx.