SOME EXPERIMENTS ON FLOW-INDUCED VIBRATION OF A CIRCULAR CYLINDER WITH SURFACE ROUGHNESS

Abstract Aeroelastic instability of a circular cylinder with surface roughness was experimentally studied by free-oscillation tests in a wind tunnel. Flows at high Reynolds numbers could be simulated at relatively low wind velocities, by introducing surface roughness, so as to reduce the value of the critical Reynolds number. The response amplitudes of a roughened cylinder oscillating in the transverse (cross-flow) direction in the flow were measured. The measured range of reduced velocity is about 1·5–8, which includes the critical velocity. The value of a reduced mass-damping parameter (the Scruton number) is constant at about 6. For the aeroelastic instability in the transverse direction, it was found that the oscillation of the roughened cylinder induced by a vortex-excitation is damped down in a small velocity range covering the critical Reynolds number. At Reynolds numbers higher than the critical value, a roughened cylinder vibrates with a large amplitude again, associated with a lock-in phenomenon due to the coincidence of the wake-frequency and the natural frequency of the oscillating cylinder.