Towards an understanding of the marine fouling effects on VIV of circular cylinders: Response of cylinders with regular pyramidal roughness

• In-water small scale towing-tank experiments in a uniform flow were conducted.
• Effects of biofouling on the dynamics of the VIV in inclined cylinders were studied.
• The fouling played important roles in the overall wake dynamics and the cylinder response.
• The biofouling almost decreases the non-dimensional amplitude and flow forces.
• Flow visualisation showed that the separation was delayed. Moreover, the biofouling shortened the vortices size and recirculation length.

sUnderwater surface of man-made structures is quickly covered by unwanted aquatic organisms. They change the flow regime around the structure. Despite the important contributions of previous studies on the vortex induced vibration (VIV) of bluff bodies, the flow induced vibration of non-stationary cylinders covered by marine fouling appears not to have received due attentions in the literature. The current paper reports on an attempt for better understanding the marine fouling effects on the VIV of circular cylinders. A structured review of the literature related to the fluid structure interactions in marine fouled cylinders is first presented. Results of an experimental study on the VIV of low mass-damping circular cylinders with artificial marine fouling are then reported. The fouling was simulated by uniformly distributed pyramids on the surface of the test cylinders. The Reynolds number ranged from 3.5 × 103 to 3.5 × 104.The experimental results showed that, the peak VIV amplitude, the synchronisation range, the lift force coefficient, the mean drag coefficient and the RMS of the fluctuating drag coefficient were decreased by the fouling. Flow visualisation showed that the separation was delayed and the vortices size and recirculation length became shorter in the fouled cylinder. In general, it appeared that the fouling was acting, to some degrees, as a VIV suppression tool.