Prof. Peter Read

Abstract:

Results from an experimental study of vortices in a rotating shear layer will be presented. Through the rotation of circular sections in the base and lid of a circular tank, a vertical shear layer is created in the fluid interior. In supercritical conditions, the flow is in the form of a regular string of two-dimensional, vertically uniform, vortices along the now wavy shear layer. Once established, the vortices are very stable flow structures that persist as long as the shear is maintained. Under most conditions the vortices were steady, but quasi-periodic and chaotic flows were also observed. The data from the experiments are in the form of maps of the instantaneous horizontal velocity field obtained by a particle tracking technique similar to Particle Image Velocimetry (PIV). The data would be useful validate both the spatial and temporal behaviour of numerical models.

Abstract:

The Proper Orthogonal Decomposition (POD) is a procedure to compute an orthogonal basis from a time series of spatial fields. This basis is optimal among all linear decompositions, in the sense that for a given number of modes, the projection of the original signal onto the subspace will contain the most variance on average. This algorithm is applied to streamfunction fields derived from measurements of the flow in the thermally forced rotating annulus experiment. Results of this analysis are presented, and a method to derive low-dimensional models of the flow by projecting the equations of motion onto these empirical eigenfunctions is discussed.