Flow around a Circular Cylinder in the High Reynolds Number Range : Effect of Surface Roughness

Abstract

Experimental investigations of the effect of the relative roughness on the transition of flow were examined in the Reynolds numbers range of 5×10⁴≤Re≤10⁷, using 8 cylinders with different relative surface roughnesses. Flow phenomena on the cylindrical surface are classified in four types irrespective of surface roughness. They are: subcritical, transitional, supercritical and transcritical regions. These regions are classified from the variations in the drag coefficient and Strouhal number with Reynolds number. The Reynolds number range at the interface of these flow regions, the variation procedure and the degree of variation, depend on the relative roughness. For example, the Reynolds number at the interface between the subcritical and transitional ranges can be properly determined as a transitional point of relation between the drag coefficient and the base pressure coefficient. With an increase in the surface roughness, the interface points shift into the lower Reynolds number range. The effect of the relative roughness on these flow phenomena is classified and discussions are also made.