Effects of Natural Frequency Ratio on Flow Around an Elastically Supported Circular Cylinder

Abstract

In this study two-dimensional incompressible Newtonian fluid flow around a freely vibrating circular cylinder is analyzed using a CFD approach. In these computations Reynolds number, mass ratio and structural damping coefficient values are fixed at 150, 8/π and 0, respectively. Computations are carried out at the streamwise to transverse natural frequency ratio range of FR = 1– 3 at fv/fNy =0.9, 1.0 and 1.1, where fv is the vortex shedding frequency for a stationary cylinder and fNy is the natural frequency in transverse direction. It was found that both FR and fv/fNy strongly influence the vibration amplitudes in the streamwise and transverse directions. Distorted figure-eight cylinder motion was identified in all cases investigated. Cylinder paths are asymmetrical in the domain between FR = 2 and 2.6 and symmetrical below and above this range. For symmetrical paths 2S vortex structures were identified and P+S vortex shedding modes were found for asymmetrical paths. In the frequency spectra of lift f/fNy = 1 and 3 frequency peaks were found to play important roles. They affects for example the vortex structure and the cylinder trajectory.