Numerical simulation of vortex-induced vibration of a circular cylinder with different surface roughnesses

The effects of surface roughness on the vortex-induced vibration (VIV) performances of a circular cylinder were studied numerically. The VIV response amplitude, response frequency, vortex force, vortex phase and vortex shedding flow pattern with different degrees of surface roughness were compared. The numerical results show that the VIV response amplitude decreases with increased surface roughness. For a smooth cylinder and a cylinder with small surface roughness, the VIV response could be divided into three branches: initial branch, upper branch and lower branch. In the initial and upper branches, the vortex shedding flow pattern displays a 2S mode. However, the VIV response produces a 2P mode vortex shedding pattern in the lower branch. For a cylinder with large surface roughness, the VIV response can be divided into only two branches: an initial branch and a lower branch. In the initial branch, the vortex shedding flow pattern displays a 2S mode, but in the lower branch, the pattern changes to the 2P mode. The transition of 2S mode to 2P mode is caused by the abrupt change of the vortex phase between the vortex force and the VIV response.