Vortex shedding from bluff bodies and a universal Strouhal number

Experiments on vortex shedding from bluff bodies were conducted in a wind tunnel, with emphasis on finding the effects of afterbody shape on the vortex-shedding frequency. It is found that the Strouhal number of a bluff body with afterbody decreases initially with increasing side ratio, with a reduction that is not dependent on the details of afterbody shape but only on the side ratio. This is in sharp contrast to the base suction that is sensitively dependent on afterbody shape. Two normal plates in tandem arrangement are exceptional in that the Strouhal number increases initially with increasing gap between the two plates. The inapplicability of Roshko's universal Strouhal number to bluff bodies with afterbodies is mentioned and discussed in some detail. (C) 1966 Academic Press Limited