An investigation into the formation of buoyancy driven streamwise vortices

Abstract

An investigation was conducted into the formation and development of streamwise thermal vortices, which were observed in a natural convection test rig. The formation mechanism of these vortices and the mechanism which determines the vortex wavelength is not well understood. A numerical investigation into these mechanisms using Large Eddy Simulations was conducted.A method for the formation of the streamwise vortices has been proposed. The mechanism involved the interaction of an incoming boundary layer vortex with buoyancy forces from a heated wall. This interaction causes the incoming boundary layer vortex to roll up into counter-rotating vortex pairs.Studies to understand factors affecting the wavelength of the vortices were conducted. One study looked at the effect of different wall temperatures on the wavelength. It was found the variation in wavelength with temperature agreed well with existing experimental data. Another study looked at the effect of fluid properties on the wavelength. This study involved simulations that doubled or halved the fluid viscosity and thermal conductivity. It was then shown that the variation in wavelength with temperature was not due to changes in fluid properties with temperature.