Preprints
https://doi.org/10.5194/wes-2021-70
https://doi.org/10.5194/wes-2021-70

  12 Jul 2021

12 Jul 2021

Review status: this preprint is currently under review for the journal WES.

Experimental analysis of radially resolved dynamic inflow effects due to pitch steps

Frederik Berger1, David Onnen1, J. Gerard Schepers2,3, and Martin Kühn1 Frederik Berger et al.
  • 1ForWind - Center for Wind Energy Research, University of Oldenburg, Institute of Physics, Küpkersweg 70, 26127 Oldenburg, Germany
  • 2TNO Energy Transition, Petten,1755 LE, The Netherlands
  • 3Hanze University of Applied Sciences, Groningen, 9747 AS, The Netherlands

Abstract. The dynamic inflow effect denotes the unsteady aerodynamic response to fast changes in rotor loading due to a gradual adaption of the wake. This does lead to load overshoots. The objective of the paper was to increase the understanding of that effect based on pitch step experiments on a 1.8 m diameter model wind turbine, which we performed in the large open jet wind tunnel of ForWind – University of Oldenburg. We measured the flow in the rotor plane with a 2D Laser Doppler Anemometer and were able to extract the dynamic wake induction factor transients in axial and tangential direction. Further, integral load measurements with strain gauges and hot wire measurements in the near and close far wake were performed. Our results show a clear gradual decay of the axial induction factors after a pitch step, giving the first direct experimental evidence of dynamic inflow due to pitch steps. We fitted two engineering models to the induction factor transients to further investigate the relevant time constants of the dynamic inflow process.We discussed the radial dependency of the axial induction time constants as well as the dependency on the pitch direction. We confirmed that the nature of the dynamic inflow decay is better described by two rather than only one time constant. The dynamic changes in wake radius were connected to the radial dependency of the axial induction transients. In conclusion, the comparative discussion of inductions, wake deployment and loads facilitated the improved physical understanding of the dynamic inflow process for wind turbines. Furthermore, these measurements provide a new detailed validation case for dynamic inflow models and other types of simulations.

Frederik Berger et al.

Status: open (until 23 Aug 2021)

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Frederik Berger et al.

Frederik Berger et al.

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Short summary
Dynamic inflow denotes the unsteady aerodynamic response to fast changes in rotor loading and leads to load overshoots. We performed a pitch step experiment with the MoWiTO 1.8 in the large wind tunnel of ForWind – University of Oldenburg. We measured axial and tangential inductions with a recent method with a 2D-LDA system and performed load and wake measurements. These radius resolved measurements allow for new insights into the dynamic inflow phenomenon.