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

TLDR

The experiments were conducted in atmospheric and high‑pressure wind tunnels, first testing a smooth cylinder and then cylinders with relative roughnesses ks/d = 75×10⁻⁵, 300×10⁻⁵, 900×10⁻⁵, and 3000×10⁻⁵. Roughness increased the Strouhal number in the critical flow regime, reduced the step size with higher roughness, and produced a consistent Sr≈0.25±0.018 at transcritical conditions, while a smooth cylinder of l/d=3.38 showed no regular shedding but a longer cylinder (l/d=6.75) produced periodic wake fluctuations.

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 k s / 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.