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Analysis of Unsteady Hydrodynamics Related to Vortex Induced Vibrations on Bluff-Bodied Offshore Structure

[+] Author Affiliations
Mandar Tabib, Adil Rasheed

SINTEF Digital, Trondheim, Norway

Franz Georg Fuchs

SINTEF Digital, Oslo, Norway

Paper No. OMAE2017-61207, pp. V002T08A027; 8 pages
doi:10.1115/OMAE2017-61207
From:
  • ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering
  • Volume 2: Prof. Carl Martin Larsen and Dr. Owen Oakley Honoring Symposia on CFD and VIV
  • Trondheim, Norway, June 25–30, 2017
  • Conference Sponsors: Ocean, Offshore and Arctic Engineering Division
  • ISBN: 978-0-7918-5764-9
  • Copyright © 2017 by ASME

abstract

Flows around a fixed cylinder with uniform and pulsating inflow conditions at different Reynolds numbers are simulated using Large Eddy Simulation (LES). For pulsating inflow, a sinusoidal profile, with an amplitude ΔU and a pulsation frequency fe, is superimposed onto the mean velocity U at the inlet plane. The current study reveals that the pulsation can influence flow-physics in three possible ways as compared to uniform inflow conditions: (a) The vortex shedding pattern is seen to be more asymmetric for pulsating inflow than for uniform inflow. This needs to be validated with an experimental campaign devoted to the study of flow-asymmetricity due to pulsatile and uniform flow condition. (b) The dominant shedding frequency fd gets locked with respect to the frequency of the pulsating inflow fe, (for both the turbulent and transition regime) at a ratio of fe/fs0 equivalent to 0.65 – 0.75 (where fs0 is the vortex shedding frequency for uniform inflow) and ε = ΔU / (2πfeD) ≈ 0.2, where D is the diameter of the cylinder. This numerical observation is validated using the experimentally observed turbulent vortex regime work ( [1])in this range. For conditions with fe/fs0 > 0.75 the lock-in may happen at fe/2. (c) Compared to uniform inflow, the pulsating inflow leads to a larger drag coefficient. The drag coefficient is influenced by the ratios fe/fs0 and ΔU / U.

Copyright © 2017 by ASME

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