An Experimental and Numerical Study of the Effects of Surrounding Disturbances on Vortex Rings

Abstract

In this thesis, the effect of the following three aspects related to the generation and efficient transport of vortex rings were studied. They included: 1) the initial boundary condition where the vortex ring is generated. A comparison between previous results and the data obtained in this study showed that vortex rings generated at a tube orifice were both slower in velocity and larger in size than vortex rings generated at a plate orifice under similar conditions. 2) the presence of a stratified layer of fluid in a vessel. Flow visualization experiments showed that after a vortex ring penetrated through the interface of the stratified layer, it was able to mix the fluid inside the ring with the surrounding fluid. The amount of mixing depended on the depth of penetration of the ring into the stratified layer. An empirical relationship was obtained to predict the maximum penetration depth of a vortex ring into a stratified layer. It is: Xp/Rm - -29.7 log10Ri - 22.7 3) the proximity of a wall or another vortex ring to the path of the primary ring. Through numerical simulation, it was shown that the primary ring would slow down and turn away from its original path. Eventually, this ring would either crash into the wall or collide with another ring. In order to prevent this turning of a vortex ring from happening, the centre of the generation orifice should be 7.5 times the radius of the injection orifice (Rm) from the wall or (Rm) between two generation orifices. These results can be used to optimize the design and positioning of vortex ring mixers for various mixing vessel geometries and mixing processes.