Effect of surface roughness on vortex-induced vibration response of a circular cylinder

The effects of surface roughness on the vortex-induced vibration (VIV) characteristics of a circular cylinder were studied numerically. The response amplitude, vortex shedding frequency, structural vibration frequency, lock-in region, vortex shedding flow pattern and hydrodynamic coefficient with different degrees of surface roughness were compared. The numerical results show that the reduced velocity could be divided into four parts: initial branch, upper branch, lower branch and desynchronisation region based on the VIV response amplitude and frequency. During initial branch, the obvious pure lock-in phenomenon can be found; however, in upper and lower branches, dual lock-in is detected. Rough cylinders have a smaller VIV displacement and a narrower lock-in region than a smooth cylinder. However, the vortex shedding flow pattern has not affected by the surface roughness. As surface roughness increases, the Strouhal number tends to increase; however, the mean drag coefficient has a decreasing tendency.