MODEL FOR THE TRANSITION IN BLUFF-BODY WAKES

The transition from a periodic vortex street to a less ordered state o f vortex shedding in the wake of elongated bluff bodies is investigate d in the case of a ring. Experimental results characterizing this tran sition are presented. The complex Ginzburg-Landau model, which is know n to accurately describe the periodic regime, is extended to the trans ition range, and its predictions are compared to the experimental find ings. The good agreement allows interpretation of the instability of t he periodic vortex shedding in terms of the Benjamin-Feir instability of a one-dimensional system of coupled nonlinear oscillators.