Vortex Excited Oscillation of a Circular Cylinder in a Uniform Flow

Abstract

Effects of a yaw angle on the vortex shedding frequency from a fixed circular cylinder were examined using a wind tunnel. Then, oscillations of an elastically supported cylinder whose motion was confined normal to its axis and the flow were investigated. The cosine law was confirmed to be applicable to the larger value of Reynolds number and/or the yaw angle for the vortex shedding frequency fro ma fixed cylinder. For an elastically supported cylinder a purely translational mode oscillation was observed at a low velocity. However, a rotaional mode oscillation was often superposed for higher velocities. The frequencies of these two modes of an oscillation were equal to their natural frequencies f_nz and f_nθ irrespective of the vortex shedding frequency f_vm. The translation mode oscillation had two resonance peaks at f<vm>/f_nz=1 and 2.6, whereas the rotation mode had only one peak at f_vm/f_nθ=2.8. A yaw angle made the vortex shedding irregular, making the resonance phenomena unclear for both the translation and the rotation modes.