Appraisal of universal wake numbers from data for roughened circular cylinders

An analysis was carried out to check whether certain existing universal wake numbers can characterize the cross-flow around roughened circular cylinders in transitional regimes. The results confirmed the soundness of the idea of the existence of a link between the drag coefficient of a bluff body, its pressure distribution, and the frequency of the shedding of vortices in its wake. In particular, Bearman's number and Griffin's number were shown to be able to describe this link with sufficient accuracy and to be a function of the Reynolds number based on the typical dimension of the surface roughness. A physical interpretation of Griffin's number was also given which permits to link the drag force with the velocity of the potential flow at separation and the frequency of vortex shedding.