Experimental study on transverse flow-induced oscillations of a square-section cylinder at low mass ratio and low damping

Abstract

This article presents experimental results concerning the transverse flow-induced oscillations of a square-section cylinder for several values of the mass ratio, ranging from 2.2 to 14.4, and low mechanical damping. Experiments were carried out in a re-circulated free-surface water channel. A rigid square-section cylinder was fixed to an elastic system made with dual (parallel) metallic blades connected by a rigid block. By this way the square-section cylinder is free to oscillate in the transverse (normal to flow) direction. The elastic system presents linear behavior in terms of stiffness and damping. The functional dependence between the steady-state amplitude and frequency of oscillations with reduced velocity is characterized. A re-normalization plot appears when steady-state amplitude of oscillations is plotted against the “true” reduced velocity, which is defined as the reduced velocity divided by the dimensionless frequency of oscillations. Experiments also allow to discuss other aspects, like the reduced velocity at which oscillations are expected to start depending on the value of the mass ratio, how close to sinusoidal (say, fixed amplitude and frequency) the oscillations are, or when quasi-steady conditions are expected to be met.