Downwind pre‐aligned rotors for extreme‐scale wind turbines

Loth, Eric; Steele, Adam; Qin, Chao; Ichter, Brian; Selig, Michael S.; Moriarty, Patrick

doi:10.1002/we.2092

Cited by 59 publications

(55 citation statements)

References 28 publications

(52 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Wind turbine blade mass typically scales with R 2.2 , which is consistent with the 13.2‐MW turbine designed by Sandia National Labs . However, at extreme‐scale, the downwind thrust forces are no longer small relative to centrifugal forces.…”

Section: Extreme‐scale Load‐aligned Wind Turbinessupporting

confidence: 59%

“…Wind turbine size (rotor diameter and hub height) is a primary factor determining a wind turbine's energy production. Larger turbines have larger swept areas and reach higher into the atmosphere, accessing stronger, and more consistent winds due to reduced effect of the boundary layer, which can increase their net power . This has led many to view extreme‐scale wind turbines (rated power exceeding 10 MW) as an effective way to lower levelized cost of energy (LCOE).…”

Section: Extreme‐scale Load‐aligned Wind Turbinesmentioning

confidence: 99%

“…The translational portion of the transformation is not captured by the Q matrix and must be later accounted for. The rotor frame (e r ) compared with inertial frame (e i ) is first rotated by τ about -e i,2 and then rotated by ψ about e i, 1 . There is no translation between the two frames.…”

Section: Fundingmentioning

confidence: 99%

See 2 more Smart Citations

Analytic analysis of load alignment for coning extreme‐scale rotors

2019

Self Cite

View full text Add to dashboard Cite

Extreme-scale wind turbines (rated powers greater than 10 MW) with large rotor diameters and conventional upwind designs must resist extreme downwind and gravity loads. This can lead to significant structural design challenges and high blade masses that can impede the reduction of levelized cost of wind energy. Herein, the theoretical basis for downwind load alignment is developed. This alignment can be addressed with active downwind coning to reduce/eliminate flapwise bending loads by balancing the transverse components of thrust, centrifugal, and gravitational force.Equations are developed herein that estimates the optimal coning angle that reduces flapwise loads by a specified amount. This analysis is then applied to a 13.2-MW scale with 100-m-level wind turbine blades, where it is found that a load alignment coning schedule can substantially reduce the root flapwise bending moments. This moment reduction in this example can allow the rotor mass to be decreased significantly when compared with a conventional upwind three-bladed rotor while maintaining structural performance and annual energy output. KEYWORDSdownwind turbines, morphing hinge, load-aligned, precone, prealigned | EXTREME-SCALE, LOAD-ALIGNED WIND TURBINESWind turbine size (rotor diameter and hub height) is a primary factor determining a wind turbine's energy production. Larger turbines have larger swept areas and reach higher into the atmosphere, accessing stronger, and more consistent winds due to reduced effect of the boundary layer, which can increase their net power. 1 This has led many to view extreme-scale wind turbines (rated power exceeding 10 MW) as an effective way to lower levelized cost of energy (LCOE). For example, the European UpWind project predicted that 20 MW (252-m rotor diameter) wind turbines might be possible for off shore conditions. 2 General Electric 3 has released plans to build a 12-MW off-shore wind turbine with a rotor Nomenclature: F , Force acting on the blade; m, Mass; M, Root flapwise bending moment; P, Generator power; r, Coordinate in the radial direction from the center of rotation; R, Tip radius; R h , Hub radius; s, Coordinate from the blade root in the direction of the blade tip; S, Blade length; t, Coordinate from the blade root in the transverse direction; U∞, Free stream wind velocity; x, Coordinate from the center of rotation in the free stream wind direction; y, Coordinate from the center of rotation in the direction defined by ey = ez × ex; z, Coordinate from the center of rotation in the vertical direction; β, Coning angle; β 0 , Coning angle resulting an average root flapwise bending moment of zero; β2/3, Coning angle which reduces average root flapwise bending moment to 2/3 of original; λ, Tip speed ratio; τ, Shaft tilt angle; ψ, Azimuth angle (ψ = 0°when the blade points up); ω, Rotational rate of the rotor; () C , Component from centrifugal force; ()c, Conventional value (from simulation); ()G, Component from gravity; ()T, Component from thrust; []′, Distributed along the span of the bladeNovelty s...

show abstract

Section: Extreme‐scale Load‐aligned Wind Turbinessupporting

confidence: 59%

Section: Extreme‐scale Load‐aligned Wind Turbinesmentioning

confidence: 99%

See 1 more Smart Citation

Analytic analysis of load alignment for coning extreme‐scale rotors

2019

Self Cite

View full text Add to dashboard Cite

show abstract

“…Another concept to reduce mass-scaling issues is a highly coned, downwind rotor, which has shown that blade loads can be reduced by converting large cantilever loads at the blade root into tensile loads along the span of the blade (Ichter et al, 2016;Loth et al, 2017b). We will analyze this concept and its effect on the structural loading of the other wind turbine components besides the blades.…”

Section: Introduction 15mentioning

confidence: 99%

System-level design studies for large rotors

Zalkind¹,

Ananda²,

Chetan³

et al. 2019

Preprint

Self Cite

View full text Add to dashboard Cite

Abstract. We examine the effect of rotor design choices on the power capture and structural loading of each major wind turbine component. A steady-state, harmonic model derived from simulations using the NREL aeroelastic code FAST is developed 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 calibrate the harmonic model and quantify uncertainty. Our design studies highlight both industry trends and innovative designs: we progress from a conventional, upwind, 3-bladed rotor, to a rotor with longer, more slender blades that is downwind and 2-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, 2-bladed rotor design is analyzed, with a focus on its ability to reduce peak blade loads by 10 % per 5 deg. of cone angle, and also reduce total blade mass. However, when compared to conventional, 3-bladed, upwind designs, the peak main bearing load of the up-scaled, downwind, 2-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.

show abstract

“…Innovations that can reduce loads can allow for larger turbines, which generate more power and still allow for a decreased cost of wind energy. One such innovation is the downwind load‐aligned wind turbine . Downwind indicates the rotor is positioned downstream of the tower.…”

Section: Introductionmentioning

confidence: 99%

Tower shadow induced blade loads for an extreme‐scale downwind turbine

2019

Self Cite

View full text Add to dashboard Cite

The downwind rotor configuration provides a structural advantage compared with an upwind design. However, tower shadow has long been a concern for downwind systems. The tower shadow negatively affects the blade by introducing a load impulse during the wake passage. An aerodynamic fairing could shroud the tower reducing the wake. However, there is no clear consensus on the importance of a tower shadow for utility-scale wind turbines. Simulations were conducted in FAST to determine the general parameters that influence the importance of the tower shadow effect for the differently sized wind turbines. The lock number of the blade was a significant driving quantity. Lower lock numbers (typical of small-scale wind turbines) lead to greater relative fatigue damage from tower shadow effects. It was determined that a fairing is very helpful for small-scale wind turbines operating in a lowturbulence environment (such as a subscale wind tunnel test). However, the tower shadow increased the damage equivalent loading on an extreme scale blade by less than 5% in a turbulent environment. These results indicate that the cost of a tower fairing is likely unnecessary for utility-scale wind turbines in operation. K E Y W O R D Stower fairing, tower shadow effect, shroud, wake model

show abstract

Downwind pre‐aligned rotors for extreme‐scale wind turbines

Cited by 59 publications

References 28 publications

Analytic analysis of load alignment for coning extreme‐scale rotors

Analytic analysis of load alignment for coning extreme‐scale rotors

System-level design studies for large rotors

Tower shadow induced blade loads for an extreme‐scale downwind turbine

Contact Info

Product

Resources

About