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Wind Energy Science The interactive open-access journal of the European Academy of Wind Energy
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Via 11 years of measurements, we made a statistical ensemble of wind speed ramps, in terms of acceleration, mean speed, and shear. Constrained turbulence and large-eddy simulations were coupled to an aero-elastic model, for each ensemble member. Ramp acceleration was found to dominate the maxima of thrust-associated loads, with a ramp-induced increase of 45–50 % plus ~3 % per 0.1 m s−2 of bulk ramp acceleration magnitude. The LES indicate that the ramps (and such loads) persist through the farm.
Preprints
https://doi.org/10.5194/wes-2021-40
https://doi.org/10.5194/wes-2021-40

  01 Jun 2021

01 Jun 2021

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

Statistical impact of wind-speed ramp events on turbines, via observations and coupled fluid-dynamic and aeroelastic simulations

Mark Kelly1, Søren Juhl Andersen2, and Ásta Hannesdóttir1 Mark Kelly et al.
  • 1Department of Wind Energy, Danish Technical University, Risø Lab/Campus, Roskilde 4000, Denmark
  • 2Department of Wind Energy, Danish Technical University, Lyngby 2800, Denmark

Abstract. Via 11 years of measurements, we calculated the probability space of expected offshore wind speed ramps, recasting it compactly in terms of relevant load-driving quantities for horizontal-axis wind turbines. A statistical ensemble of events in reduced ramp-parameter space (ramp acceleration, mean speed after ramp, upper-level shear) was created, to capture the variability of ramp parameters and also allow connection of such to ramp-driven loads. Constrained Mann-model (CMM) turbulence simulations coupled to an aero-elastic model were made for each ensemble member, for a single turbine. Ramp acceleration was found to dominate the maxima of thrust-associated loads, with a ramp-induced increase of 45–50 % for blade-root flap-wise bending moment and tower base fore-aft moment, plus ~3 % per 0.1 m s−2 of bulk ramp acceleration magnitude.

The ensemble of ramp events from the CMM was also embedded in large-eddy simulation (LES) of a wind farm consisting of rows of nine turbines. The LES uses actuator-line modelling for the turbines and is coupled to the aero-elastic model. The LES results indicate that the ramps, and the mean acceleration associated with them, tend to persist through farm. Depending on the ramp acceleration, ramps crossing rated speed lead to maximum loads, which are nearly constant for the third row and further downwind. Where rated power is not achieved, the loads primarily depend on wind speed; as mean winds weaken within the farm, ramps can again have U < Vrated. This leads to higher loads than pre-ramp conditions, with the distance where loads begin to increase depending on inflow Umax relative to Vrated. For the ramps considered here, the effect of turbulence on loads is found to be small relative to ramp amplitude that causes Vrated to be exceeded, but for ramps with Uafter < Vrated, the combination of ramp and turbulence can cause load maxima. The same sensitivity of loads to acceleration is found in both the the CMM-aeroelastic simulations and the coupled LES.

Mark Kelly et al.

Status: open (until 14 Jul 2021)

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Mark Kelly et al.

Mark Kelly et al.

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Short summary
Via 11 years of measurements, we made a statistical ensemble of wind speed ramps, in terms of acceleration, mean speed, and shear. Constrained turbulence and large-eddy simulations were coupled to an aero-elastic model, for each ensemble member. Ramp acceleration was found to dominate the maxima of thrust-associated loads, with a ramp-induced increase of 45–50 % plus ~3 % per 0.1 m s−2 of bulk ramp acceleration magnitude. The LES indicate that the ramps (and such loads) persist through the farm.
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