On uniform flow around rough circular cylinders at critical Reynolds numbers

Abstract Flow regimes around rough circular cylinders are discussed on the basis of measurements of mean and fluctuating pressures. Two regimes can be identified for cylinders with large roughness: subcritical and transcritical, separated by a critical transition occurring over a rather narrow Reynolds number range. The data show the existence of two subranges within the critical transition, the first characterized by symmetric pressure distributions, an increasing lack of uniformity along the cylinder span, and strong shedding peaks that become smaller and broader as Re increases, the second by oscillating, asymmetric pressure distributions and the disappearance of organized shedding. The transcritical regime is characterized by sharp vortex shedding peaks and the disappearance of the low frequency fluctuations that mark transitional flow ranges.