Experimental study of the effects of surface roughness on the vortex-induced vibration response of a flexible cylinder

The effects of surface roughness on the vortex-induced vibration (VIV) of a flexible cylinder have been studied experimentally. The drag, lift, tension, vortex-shedding frequency, vibration frequency, and displacement response of cylinders with different roughnesses are compared. The results indicate that a pure VIV lock-in phenomenon occurs in the in-line direction earlier than in the cross-flow direction, and thus the VIV response in the in-line direction is larger than in the cross-flow direction in the low-reduced-velocity range. The tension in the cylinder has two peak frequencies. One peak is the dominant frequency, which coincides with the dominant frequency of the drag and is induced by the VIV in the in-line direction. The other peak is at half of the dominant frequency, at the dominant frequency of the lift; it is caused by the VIV in the cross-flow direction. Rough cylinders have a smaller displacement response, a narrower lock-in region, and a higher vortex-shedding frequency than a smooth cylinder.