Control of the bistable regime in two side-by-side cylinders by mechanical rotation

F. CASTRO; R SOSA; G ARTANA

Colonia

Congreso; XI Reunión sobre Recientes Avances en Física de Fluidos y sus Aplicaciones; 2010

Instituto de Física, Facultad de Ciencias, UDELAR

A two dimensional flow behind two side-by-side circular cylinders was controlled by means of a steady rotation of one of them.For a spacing between two side-by-side circular cylinders of T/D = 1.2 (been T the gap spacing between cylinders and D the diameter) a ?ow regime in which the wake behind the cylinders is grossly unsteady and asymmetric is observed. The gap ?ow is biased toward one side or the other, and the cylinder toward which the ?ow is biased consequently has a narrower near wake and higher-frequency vortex shedding while the other cylinder has a wider near wake and lower-frequency vortex shedding. Mode ‘NW’ (narrow wake) causes a higher drag, and the mode ‘WW’ (wide wake) causes a lower drag on the respective cylinders. The biased gap ?ow is bistable and switches from one side to the other at irregular intervals of time. This regime is therefore known as a flip-flopping regime or bistable.The focus of this study was on the determination of the authority of a steady mechanical rotation to control that switching phenomena.Two side-by-side cylinders were placed in a flowing soap film resulting in a two dimensional flow at Reynolds number in the order of 1000. Wake visualizations have been done, by means of the Schilieren technique, in order to determine the flow state.