Effects of sinusoidal streamwise gust on the vortex-induced force on an oscillating 5:1 rectangular cylinder

Abstract

In the present study, the vortex-induced force was investigated for an oscillating rectangular cylinder with the side ratio of 5 ( B/D ​= ​5, B : breadth of the cylinder, D : depth of the cylinder) encountering a sinusoidal streamwise gust by wind tunnel tests and computational fluids dynamics (CFD) simulations. For the experiments part, a multiple-fan active-controlled wind tunnel was used to generate the sinusoidal streamwise gust and the vortex-induced force was measured. The results show that the component of total vortex-induced force caused by Karman vortex shedding (denoted as Karman-vortex-induced force) almost disappeared in the sinusoidal streamwise gust, while another component caused by motion-induced vortices (denoted as motion-induced force) remained almost unchanged, regardless of the gust frequency and amplitude. The CFD simulations were performed to shed light on the flow mechanism of vortex-induced force variation. It was found that the flow structure around rectangular cylinder is sensitive to the oncoming flow condition. The alternative vortex shedding in the near wake was suppressed due to the unsteady effects of sinusoidal streamwise gust, which is responsible for the disappearance of Karman-vortex-induced force. However, the vortices induced by the rectangular cylinder motion still exist and lead to the Karman vortex street in the far wake. • Experimental and numerical studies on the sinusoidal streamwise gusts over an oscillating 5:1 rectangular cylinder. • The unsteady effects of sinusoidal streamwise gusts on the vortex-induced force are investigated. • The Karman-vortex-induced force almost disappears in the sinusoidal streamwise gust. • The alternative vortex shedding in the near wake was suppressed as in the sinusoidal streamwise gust.