Laboratory experiments on eddy interaction with multiple islands

The present study investigates the interaction between a self-propagating cyclonic eddy with two right vertical cylinders and determines the conditions for an eddy to bifurcate into two or more eddies. We performed a series of laboratory experiments in a glass tank mounted concentrically on rotating turntable. The velocity and vorticity of the flow field were obtained using particle tracking velocimetry. As in previous studies, after the cyclonic eddy came in contact with the obstacle, fluid peeled off the outer edge of the vortex and a so-called “streamer” went around the cylinder in a counterclockwise direction. Under the right conditions, this fluid formed a new cyclonic vortex in the wake of the cylinder, causing bifurcation of the original vortex into two vortices. In some cases, two “streamers” formed and went around the two obstacles, each forming a new cyclonic vortex. During the experiments three parameters were varied: G, the obstacle separation, d, the diameter of the incident vortex and y, the distance of the center of the vortex from an axis passing through the center of the gap between the obstacles. The number of eddies generated by the interaction depends on the ratio G/d and on the geometry of the encounter, which is given by the ratio y/g, where g = G/2. Furthermore, when -2 < y/g < 0, 0.25  G/d  0.4 and Re > 200, we observed the formation of an eddy of opposite sign, anticyclonic. This is in agreement with recent observations of North Brazil Current Rings, suggesting that these very idealized laboratory experiments may bring some insights to the fate of mesoscale vortices in the Ocean.