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*zeta. 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*zeta is not the sole parameter influencing the response during lock-in; Reynolds number also plays an important role. If m*zeta 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*zeta 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. (c) 2008 Elsevier Ltd. All rights reserved.