| Dynamic interactions in the near wake of a bluff body placed in a laminar fluid stream give rise to a periodic array of vortices that are shed from the separating shear layers and convect downstream. Within a certain range of windspeeds, the shedding process can be 'controlled' by the dynamics of the structure, thereby tuning the fluid-structure system to a single frequency. A nonlinear feedback from the near wake to the body can then occur, leading to large amplitudes of response.;New insight was gained into the character of vortex-induced response of a circular cylinder outside and within the synchronization range.;A flexibly-suspended circular cylinder was tested for such vortex-induced vibrations in a low-speed wind tunnel. The effect of mechanical damping and fluid-structure mass-ratio were investigated. Particular attention was given to the behavior of the near wake for different wind-speeds. The response of the cylinder as well as single-point velocity fluctuations in the wake were monitored and recorded digitally. Two mathematical models--a single degree of freedom model with frequency-dependent constants and parametric excitation, and a full body-wake coupled model with nonlinear coupling--were proposed and their parameters discussed in relation to the data obtained in the wind tunnel. |
