The interaction of the piston vortex with a piston-generated vortex ring

10.1017/S0022112003006980Journal of Fluid Mechanics499327-343JFLS

Cross-sectional flow measurements during spin-down of a rotating torus

This paper reports the experimental determination of the flow structure of an outer streak observed when a rotating torus is suddenly brought to rest. Previous top-down experiments have allowed for visualisation of a streak on the inner wall followed by one on the outer wall, however a new experimental design has allowed for the first time cross section flow measurements to be recorded. This has led to observation of a vortex we propose is responsible for this streak when visualised top down. The flow structures observed through Particle Image Velocimetry (PIV) measurements in cross-section appears as a centrifugal instability on the inner wall leading to a vortex pair, followed by vortices on the outer wall. This appears to be highly consistent with theoretical and computational predictions. The position of this outer vortex, when normalised for the initial rotation rate of the torus, accurately tracks the position of the streak when seen from above