Effect of surface roughness on vortex-induced vibrations of a freely vibrating cylinder near a stationary plane wall

The effects of surface roughness of the vortex-induced vibration (VIV) responses of a circular cylinder near a stationary plane wall were studied using the two-dimensional unsteady Reynolds-averaged-Navier-Stokes equations and the shear stress transport k−ω model coupling with a fourth-order Runge-Kutta method. A smooth cylinder and rough cylinders with three different degrees of surface roughness were selected for the study. The VIV response amplitude, structural vibration frequency, lock-in region, vortex shedding flow pattern, Strouhal number and hydrodynamic coefficient for cylinders with different degrees of surface roughness were compared. The numerical results show that for a smooth cylinder and a cylinder with small surface roughness, the reduced velocity range can be separated into four parts based on the VIV amplitude: an initial branch, an upper branch, a lower branch and a desynchronization region. However, for cylinders with intermediate and large surface roughnesses, the upper branch is absent, leaving only three branches. The lock-in phenomenon can apparently be found for all surface roughnesses, but the width of the lock-in region is not very sensitive to the variation of the surface roughness. As surface roughness increases, the Strouhal number has an increasing tendency; however, the mean drag coefficient has a decreasing tendency.