System-level design studies for large rotors

Abstract

Abstract. We examine the effect of rotor design choices on the power capture and structural loading of each major wind turbine component. A harmonic model for structural loading is derived from simulations using the National Renewable Energy Laboratory (NREL) aeroelastic code FAST to reduce computational expense while evaluating design trade-offs for rotors with radii greater than 100 m. Design studies are performed, which focus on blade aerodynamic and structural parameters as well as different hub configurations and nacelle placements atop the tower. The effects of tower design and closed-loop control are also analyzed. Design loads are calculated according to the IEC design standards and used to create a mapping from the harmonic model of the loads and quantify the uncertainty of the transformation. Our design studies highlight both industry trends and innovative designs: we progress from a conventional, upwind, three-bladed rotor to a rotor with longer, more slender blades that is downwind and two-bladed. For a 13 MW design, we show that increasing the blade length by 25 m, while decreasing the induction factor of the rotor, increases annual energy capture by 11 % while constraining peak blade loads. A downwind, two-bladed rotor design is analyzed, with a focus on its ability to reduce peak blade loads by 10 % per 5∘ of cone angle and also reduce total blade mass. However, when compared to conventional, three-bladed, upwind designs, the peak main-bearing load of the upscaled, downwind, two-bladed rotor is increased by 280 %. Optimized teeter configurations and individual pitch control can reduce non-rotating damage equivalent loads by 45 % and 22 %, respectively, compared with fixed-hub designs.

Redesign of an upwind rotor for a downwind configuration: design changes and cost evaluation

“…The downwind configurations are subject to a lower AEP production due to the coning direction. This effect has also been observed by, for example, Zalkind et al (2019) and Ning and Petch (2016). In the direct comparison, the AEP of the S111dw PF is 2.04 % lower than the AEP of the comparable S111uw PF.…”

“…Future work should also consider a redesign of the nacelle for the better balancing of the rotor mass on the tower for the downwind configuration, as suggested by Zalkind et al (2019). However, it should be kept in mind that the upwind configuration will always be beneficial in terms of tower bottom bending moment.…”

“…In a system-level design study for large rotors, Zalkind et al (2019) showed that coned downwind rotors significantly reduce peak blade loads during operation but have a lower annual energy production (AEP) compared to a coned upwind configuration of the same size. While the group predicts larger main bearing peak loads for the downwind configuration related to blade length, mass, and cone angle, they suggest that the increased tower loads observed by other groups could be overcome by properly balancing the nacelle on the tower.…”

Validation of a 20 m Wind Turbine Blade Model

“…The trend in designing larger and larger horizontal axis wind turbines (HAWTs) seems to be still unbroken if one looks into the current developments and announcements in the offshore and onshore markets [1] and at the research [2]. This cost of energy-driven development comes with different challenges, as described in [3]-in particular, the precise prediction of the aeroelastic behaviour and the overall dynamics of a turbine equipped with large and very flexible wind turbine blades.…”

“…1 119.5 kg extra mass has been subtracted from the measured mass 2. 135.7 kg extra mass has been subtracted from the measured mass 3.…”