The effect of surface roughness on aerodynamic forces and vibrations for a circular cylinder in the critical Reynolds number range

The excitation mechanism of vibrations of circular cylinders in the critical Reynolds number range remains unclear. These vibrations have been observed in wind tunnels many times but rarely in the field. The surface roughness of the cylinder might be a reason for this difference. Aiming to reveal the effect of surface roughness on the aerodynamic forces and vibrations in the critical Reynolds number range, seven circular cylinders with various value of surface roughness were covered with abrasive papers and tested in stationary and elastically mounted wind tunnel tests. The results show that the surface roughness significantly influences the aerodynamic forces in the critical Reynolds number range by reducing the range of transitions on boundary layers. These influences include suppressing the jumps in lift coefficients and other phenomena that relate to a bistable state occurring only for less rough cylinders. Therefore, sufficient surface roughness can mitigate the vibrations in the critical Reynolds number range by suppressing the bistable state in which the vibrations appear.