Vortex-induced vibrations of a circular cylinder in laminar and turbulent flows

Experimental results on the behaviour of a freely vibrating circular cylinder in laminar and turbulent flows are presented. Wind tunnel tests have been performed by varying the cylinder roughness and the mass-damping parameter, m * ζ . The effects of surface roughness and flow turbulence have been considered in term of an effective Reynolds number, Re eff . In this way, it has been possible to test the sample before and after the beginning of the cylinder boundary layer transition. It has been evidenced that m * ζ is not the sole parameter influencing the response during lock-in; Reynolds number also plays an important role. If m * ζ is fixed, the responses decrease as Re eff increases. Moreover, it has been observed that the cylinder may experience vortex-induced vibrations even in the critical Re eff regime characterized by a cessation of coherent vortex shedding in steady configuration. The effects of m * ζ and Re eff on the critical velocity (the velocity at which the maximum amplitude of response is approached), on the wideness of the lock-in range, and on the wake correlation length are also discussed.