Effects of elevated inflow turbulence intensity on vortex-induced vibration of smooth circular cylinders

Experiments were conducted to investigate the effects of elevated turbulence intensity (Ti) on vortex-induced vibration (VIV) of smooth circular cylinders. A Makita-type active grid turbulence generator was used to create Ti levels of ~13% and ~19% over a Reynolds number range of 5×10³ – 3.56×10⁴. The dynamic response of the cylinder undergoing VIV is plotted as a function of reduced velocity. The results are compared to the baseline (quasi-laminar) without the active grid where Ti ~ 2.2%. The elevated Ti cases were found to result in an identifiable suppression of VIV amplitudes and the crossflow force compared to the quasi-laminar case. Elevated levels of free-stream turbulence are distributed over a large range of frequencies and are not concentrated near the natural frequency of the system; as a result, the vibration amplitudes are suppressed during lock-in. We discuss our findings by comparing plots of amplitude spectral density and phase maps of instantaneous crossflow velocities/displacements.