Systematic investigation of the tip effects on vortex-induced vibrations for circular cylinders


Duranay A. , Usta O., Kınacı Ö. K.

OCEAN ENGINEERING, vol.239, 2021 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 239
  • Publication Date: 2021
  • Doi Number: 10.1016/j.oceaneng.2021.109829
  • Title of Journal : OCEAN ENGINEERING
  • Keywords: Flow induced vibrations, Circular cylinder, Tip effects, Aspect ratio effect, REYNOLDS-NUMBER, FLOW, VIV

Abstract

This paper presents an investigation into tip effects on vortex induced vibrations (VIV) for circular cylinders. Within this context; the results of the tests, which were carried out in Istanbul Technical University Ata Nutku Circulation Channel, were validated with different studies from the literature. Then, a series of VIV tests were carried out for six different smooth circular cylinders with different aspect ratios at TrSL2 and TrSL3 flow regimes having one degree-of-freedom. In the VIV tests, the mass ratios, the aspect ratios and the spring stiffness were changed systematically and the tip effects on these parameters were investigated with respect to the VIV responses of the cylinders. An uncertainty analysis was carried out to obtain the margin of bias and precision errors on the test results of oscillation amplitude for two cylinders in initial, upper and lower branches. As the aspect ratio was increased and the edges of the cylinder got closer to the walls, the synchronization range of VIV motion initiated earlier leading to a wider synchronization range. The transitions from the upper to the lower branch encountered at almost the same reduced velocities. The tip effects were found to be more dominant when the mass ratio was smaller. After the experiments validated and verified, the cylinder was subjected to CFD simulations of forced oscillations using the experimental data of amplitudes and frequencies for two different aspect ratios. The CFD study showed reduced amplitude responses when the cross-flows were higher. Spanwise flow visualization along the cylinder revealed that cross-flows are dominant at cylinder tips with lower aspect ratios.