Vortex shedding from two cylinders of different diameters

The flow over two circular cylinders was studied with the cylinders in a staggered arrangement. Two positions of the upstream cylinder relative to the downstream cylinder were used and also two free-stream velocities. Measurements were made of the frequencies of the vortex shedding from the two cylinders and of the downstream cylinder's base pressure. The effect of changing the diameter of the upstream cylinder over a range of values close to half the diameter of the downstream cylinder was examined. It was found that lock-in occurred in which the frequency of shedding from the down-stream cylinder remained at half the frequency of shedding from the upstream cylinder over a range of the latter frequency. When the interference of the flow over the down-stream cylinder due to the upstream cylinder was small, lock-in resulted in a reduction in the downstream cylinder's base pressure. When the interference was large the occurrence of lock-in was found to depend on the Reynolds number. © 1986.