Aerodynamic characteristics and excitation mechanisms of the galloping of an elliptical cylinder in the critical Reynolds number range

The generation mechanisms of dry cable instabilities in the critical Reynolds number range are still unclear because of their complicated aerodynamic forces and a shortage of studies on the coupling process. Large amplitude vibrations of an elliptical cylinder in the critical Reynolds number range are reproduced in a wind tunnel, and displacements and wind pressure on the cylinder are recorded synchronously to illustrate the interactions between the cylinder motion and the aerodynamic forces in this study. Strong interactions are observed only when the flow starts reattaching at the rear of the cylinder in the early critical Reynolds number range, wherein the reattachment stops the Kármán vortex shedding and forms a separation bubble. Once the reattachment points move forward, large amplitude vibrations are not observed. The vibration is strongly related to the contribution of the pressure in the region of the separation bubble. The organization of aerodynamic forces along the length is also needed to cause the vibrations. The aerodynamic forces are not uniformly distributed along the cylinder in the critical Reynolds number range and they can either input or absorb energy during the vibrations.