Vortex-excited vibrations of pivoted cylinders in uniform and shear flows

The response of uniform and tapered pivoted cylinders to vortex-induced forces in uniform and shear flows has been investigated both experimentally and numerically. The experimental investigations have yielded a wealth of information on the effect of structural and flow non-uniformities on vortex-excited vibrations. Shear in the flow has been observed to increase the range of lock-in. The response of tapered cylinders to vortex-excited forces in uniform and shear flows indicates a nearly constant amplitude lock-in response. The range of lock-in is observed to be very sensitive to the shear gradient in the flow. A diffusive Van der Pol oscillator model has been employed to simulate numerically the experimental investigations. The model has been shown to be very successful in replicating the response of uniform pivoted cylinders in shear flows. The agreement between the numerically predicted and experimentally recorded amplitudes and the reduced velocities at which they occur is excellent. The agreement between the numerical predictions and experimental data is quite good for the tapered cylinder in uniform flow scenarios. The numerically predicted response amplitude curve is considerably different in shape in comparison to the experimental recorded data. The diffusive Van der Pol model, in its current form, is not capable of accurately modeling the vortex-excited response of tapered cylinders in shear flow.