The inter-relationship of drag coefficient Cd and Strouhal number St in a turbulent wake was experimentally investigated for ten cylinders of the same characteristic height d but of different cross-sections at Re = 2600 and 6000, based on the freestream velocity U and d. It is found that, although Cd and St depend strongly on the geometric cross-section of the cylinder, the product of CdSt is invariant, about 0.25, under present experimental conditions. This invariance of CdSt is further confirmed with respect to Re and angle of attack of a square cylinder based on a collection of data in the literature. It is further found that CdSt is actually the ratio of the dimensionless work done upon the fluid by the cylinder to the dimensionless wavelength.

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