SELF-ORGANIZATION IN CIRCULAR SHEAR LAYERS

Experiments on forced circular shear layers performed in both magnetiz ed plasmas and in rotating fluids reveal qualitatively similar self-or ganization processes leading to the formation of patterns of coherent vortical structures with varying complexity. In this paper results are presented from both weakly nonlinear analysis and full numerical simu lations that closely reproduce the experimental observations. Varying the Reynolds number leads to bifurcation sequences accompanied by topo logical changes in the distribution of the coherent structures as well as clear transitions in the total energy and enstrophy of the system. Various oscillating and quasiperiodic states have been found, and reg imes have been investigated that so far have been experimentally inacc essible.