Vortex shedding from two cylinders in tandem

Measurements are presented of the frequencies of vortex shedding from two cylinders in tandem. In the first set of experiments both cylinders were circular. The diameter of the downstream cylinder was 22.5 mm, and three different cylinders, having diameters 23.6 mm, 24.6 mm and 25.7 mm respectively, were used in turn as the upstream cylinder. For a constant free-stream velocity, changing the diameter of the upstream cylinder changed the frequency of vortex shedding from that cylinder. It was found that the frequency of vortex shedding from the downstream cylinder locked-in to that from the upstream cylinder such that the two frequencies were equal. In the second set of experiments the downstream cylinder was circular, but the upstream cylinder was a flat plate. The frequency of shedding from the flat plate could be easily varied by rotating the plate. It was found that for low frequencies of shedding from the flat plate the two shedding frequencies were equal, which confirmed the results of the first set of experiments. However, when the frequency exceeded a critical value, which depended on the separation distance between the cylinders, lock-in broke down and the frequencies were no longer equal. © 1988.