Mitigation of Rotor Thrust Fluctuations through Passive Pitch

Weidong Dai, Riccardo Broglia, Ignazio Maria Viola*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

A rotor blade operating in an unsteady or a sheared stream experiences force fluctuations, which increase the structural requirements for both the blades and the rotor system as a whole. In this paper, we investigate whether force fluctuations can be passively mitigated without compromising the mean load. We consider a tidal turbine rotor in a shear current at a diameter-based Reynolds number of 2 × 10^7 . The blades are rigid and can passively pitch. A mass-spring system acts on the spanwise axis of the blade governing the pitch kinematics. The effectiveness of this system is demonstrated with three methodologies: an analytical model based on blade element momentum theory and Theodorsen’s theory, and two sets of Reynolds-averaged Navier-Stokes simulations performed with two independent codes. The analytical and the numerical models are validated against experiments and simulations in the literature. All methodologies predict a reduction of more than 80% of the thrust fluctuations. Furthermore, because of the more uniform thrust force exerted on the current, the wake behind a passive pitch blade does not diffuse the onset shear flow. This results in a more sheared wake and in faster wake recovery. The present results demonstrate the potential benefits of passive pitch and may underpin future applications of this concept for different types of turbines and compressors, including wind turbines, propellers, helicopter rotors, etc.
Original languageEnglish
Article number103599
JournalJournal of fluids and structures
Volume112
Early online date20 May 2022
DOIs
Publication statusPublished - Jul 2022

Keywords / Materials (for Non-textual outputs)

  • Turbine rotor
  • Unsteady loads
  • Tidal energy
  • Passive pitch
  • Morphing blade
  • Fluid-structure interaction

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