One and two degrees-of-freedom Vortex-Induced Vibration experiments with yawed cylinders

Vortex-Induced Vibration (VIV) experiments were carried out with yawed cylinders. The purpose was to investigate the validity of the Independence Principle (IP) for properly describing the flow characteristics and the dynamics of structures subjected to oblique flow. Five yaw angles in relation to the direction perpendicular to the free stream velocity were tested, namely View the MathML sourceθ=0°,10°,20°,30° and 45°. Both the upstream and downstream orientations were tested. The models were mounted on a leaf spring apparatus that allows experiments with one or two degrees of freedom. The Reynolds numbers based on the component normal to the cylinder axis fell in the interval 3×103<Ren<1.5×1043×103<Ren<1.5×104. The mass ratio parameter was m⁎=2.6m⁎=2.6 and the cylinder aspect ratio was L/D≈13L/D≈13 for all the experiments. Time histories of displacement and hydrodynamic forces were acquired. Considering only the component of the free stream which is normal to the cylinder axis, the results of amplitude and force coefficients agreed reasonably well with the non-yawed ones for yaw angles up to 20° for both one and two degrees-of-freedom experiments. This indicates the validity of the IP for this yaw angle range. For yaw angles larger than 20°, a decrease in the maximum amplitude was observed. The decrease in the oscillation amplitudes was related to a larger modulation in the phase shift between force and displacement. Differences in the results for upstream and downstream were observed and were more evident for the larger yaw angle. These differences can be associated to the asymmetric cylinder end conditions.

We would like to acknowledge the financial support provided by FINEP, CNPq and FAPESP. G.R.F would like to acknowledge FAPESP for the PhD scholarship (process 2008/00688-4) provided during the development of this work. The authors are also in debt to Prof. Celso P. Pesce, Prof. Clóvis A. Martins and Alfredo Neto for all the useful comments regarding the elastic base design. Special thanks to Cesar Freire, Ivan Korkischko, Douglas Silva, Reinaldo Marcondes Orselli, Rafael Gioria and Pedro Melo for their valuable help with the experiments and the discussion. Prof. Fujarra is grateful to the Brazilian Navy and Maritime Research Institute Netherlands for all the support provided during his sabbatical period, 2011-2012

CNPQ