Galloping mechanism of a rectangular cylinder

In case of a square cylinder the response of divergent oscillations in heaving mode, namely galloping, can be predicted by means of the quasi-steady theory. But for a rectangular cylinder with depth( D )/ breadth( B ) ratio of 2.0, the theory cannot predict the response with sufficient accuracy. In addition, the difference in amplitude of response is small, even if the difference in the mass-damping parameter is large. Moreover, in case of low mass ratio, it is found that the amplitude of response becomes larger due to the decrease in dominant frequency of response from the natural frequency. This paper investigates the mechanism of these particular phenomena in galloping oscillations of a rectangular cylinder by means of the three-dimensional simulations of fluid flows around the cylinder. The numerical method is much useful in understanding the flow structures and the aerodynamic forces in detail.