Vortex Evolution in Realistic Geophysical Flows.

Abstract

Abstract : Laboratory experiments and numerical simulations of vortex evolution in realistic geophysical flows are reported. Two laboratory experiments are discussed. The first experiment examined three dimensional vortices produced from a wing in a nonstratified nonsheared flow. This study showed that vortices can migrate farther and last longer than previously reported. The second laboratory experiment investigated the evolution of two dimensional vortices in a stratified shear flow. This experiment showed the evolution of a solitary vortex when the background Richardson number was around four or less. Circulation estimates were also obtained for these vortices and showed a more rapid decay of circulation of the countersign vortex. Two numerical studies are also reported. In the first numerical study, we examined the evolution of a two dimensional vortex pair in a stratified shear flow. This study showed that the vortex pair evolved into a solitary vortex when the ambient Richardson number was on the order of unity or less. A second numerical study used a k-epsilon model to examine the evolution of a two dimensional vortex pair. It was found that the standard k-epsilon model did a poor job of representing the turbulent dissipation in vortex flows. Good agreement with experimental results was obtained with this model with a reduction in the eddy viscosity coefficient.