There is no critical mass ratio for galloping of a square cylinder under flow

The flow-induced vibration of square cylinders under flow is known to be caused by two distinct mechanisms of interaction: vortex-induced vibrations and galloping. In the present paper we address the issue of the apparent suppression of galloping when the mass ratio between the solid and the fluid is low enough. By using a reduced-order model that we validate on pre-existing results, we show that galloping is actually not suppressed, but delayed to higher values of the flow velocity. This is explained using a linear stability analysis where the competition between unstable modes is related to the transition between vortex-induced vibration and galloping. Direct numerical simulations coupled with a moving square cylinder confirm that galloping can be found even at very low mass ratios.