An Experimental Study of Fusion of Vortex Rings

Citation

Schatzle, Paul Russell (1987) An Experimental Study of Fusion of Vortex Rings. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/KK00-ZJ41. https://resolver.caltech.edu/CaltechETD:etd-04232004-092555

Abstract

A two-component laser-Doppler velocimeter with frequency bias is used to measure the velocity field produced by the oblique collision of two laminar vortex rings. The Reynolds number, defined here as the ratio of ring circulation to kinematic viscosity, is about 1800. The rings are generated underwater and approach each other along intersecting paths. The plane defined by the two paths is a plane of symmetry, and is the plane in which the measurements were done. The out-of-plane components of vorticity and strain rate are computed from finite differences of the velocity data. The state of the rings prior to the collision is determined in order to provide a set of starting conditions for future numerical simulations. In addition, the circulation of each vortex core is computed as a function of time during the collision.

The principal result of this work is that the circulation of each vortex core is observed to decrease during the interaction; furthermore, the fluid viscosity is shown to be responsible for this decrease. The exact mechanism by which the reduction in circulation is effected is unclear, but it appears to be related to the out-of-plane stretching. A time scale is proposed for this cancellation process which combines the effects of viscosity and stretching.

The measurements also show that the structure of the vorticity field changes during the collision. In particular, each vortex core is observed to split into two vortices under the action of the local in-plane strain field.

Thesis Files