On vortex shedding from smooth and rough cylinders in the range of Reynolds numbers 6×103 to 5×106

Abstract

The influence of surface roughness on the vortex-shedding frequency in the wake of a single cylinder has been investigated. The experiments were carried out in an atmospherical and a high-pressure wind tunnel. The tests were started with a smooth cylinder. Then the wake flow of cylinders with relative roughnesses of ks/d = 75 × 10−5, 300 × 10−5, 900 × 10−5, and 3000 × 10−5 was investigated.For all roughness parameters tested the Strouhal number exhibited an increase in the critical flow regime. With growing roughness parameter the step in the curve became smaller. At transcritical flow conditions the Strouhal number was measured to be in the range of Sr = 0·25 ± 0·018 for all surface roughness tested. No regular vortex shedding could be observed in the critical flow range for the smooth cylinder with l/d = 3·38. When prolonging the test body to l/d = 6·75 the wake fluctuations became periodic.