The simultaneous effect of a fairing tower and increased blade flexibility on a downwind mounted rotor

Reiso, Marit; Muskulus, Michael

doi:10.1063/1.4803749

Cited by 15 publications

(16 citation statements)

References 10 publications

(10 reference statements)

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“…For example, the European UpWind project predicted that 20 MW (252‐m rotor diameter) wind turbines might be possible for off shore conditions . General Electric has released plans to build a 12‐MW off‐shore wind turbine with a rotor radius ( R ) of 110 m. However, any percent increase in annual energy production (AEP) should be ideally larger than the corresponding percent increase in capital and operational expense (CAPEX and OPEX) so that there is a net decrease of LCOE for the system . Off‐shore wind turbines have some advantages and disadvantages compared with on‐shore wind turbines.…”

Section: Extreme‐scale Load‐aligned Wind Turbinessupporting

confidence: 59%

Analytic analysis of load alignment for coning extreme‐scale rotors

2019

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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...

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Section: Extreme‐scale Load‐aligned Wind Turbinessupporting

confidence: 59%

Analytic analysis of load alignment for coning extreme‐scale rotors

2019

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“…This conceptual change should target the load and mass reduction of large scale wind turbines to reduce the costs. Two-bladed downwind turbines may reduce the disadvantages of upscaling that are observed for the three-bladed upwind turbine of this study, since the downwind rotor reduces the effect of tower-clearance on rotor mass [73,74]. This, in turn, mitigates the loads.…”

Section: Challenges Of Larger Wind Turbinesmentioning

confidence: 79%

Multidisciplinary design optimization of large wind turbines—Technical, economic, and design challenges

Ashuri

Zaaijer

Martins

et al. 2016

Energy Conversion and Management

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a b s t r a c tWind energy has experienced a continuous cost reduction in the last decades. A popular cost reduction technique is to increase the rated power of the wind turbine by making it larger. However, it is not clear whether further upscaling of the existing wind turbines beyond the 5-7 MW range is technically feasible and economically attractive. To address this question, this study uses 5, 10, and 20 MW wind turbines that are developed using multidisciplinary design optimization as upscaling data points. These wind turbines are upwind, 3-bladed, pitch-regulated, variable-speed machines with a tubular tower. Based on the design data and properties of these wind turbines, scaling trends such as loading, mass, and cost are developed. These trends are used to study the technical and economical aspects of upscaling and its impact on the design and cost. The results of this research show the technical feasibility of the existing wind turbines up to 20 MW, but the design of such an upscaled machine is cost prohibitive. Mass increase of the rotor is identified as a main design challenge to overcome. The results of this research support the development of alternative lightweight materials and design concepts such as a two-bladed downwind design for upscaling to remain a cost effective solution for future wind turbines.

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“…6 A recent study by Reiso on downwind turbines suggested that blade mass could be reduced by 20% with a corresponding 5% reduction in blade fatigue loads without sacrificing power. 7 This study found that benefits to the blades came at the expense of a 20% larger tower bottom bending moment, although no assessment was made on the corresponding impact to the tower mass or system costs. They also showed that while even more flexible blades were feasible, they led to decreases in power production.…”

Section: Introductionmentioning

confidence: 88%

“…Increased fatigue damage from the tower shadow becomes a concern, but may be alleviated through aerodynamic fairing on the tower or other means . A recent study by Reiso on downwind turbines suggested that blade mass could be reduced by 20% with a corresponding 5% reduction in blade fatigue loads without sacrificing power . This study found that benefits to the blades came at the expense of a 20% larger tower bottom bending moment, although no assessment was made on the corresponding impact to the tower mass or system costs.…”

Section: Introductionmentioning

confidence: 99%

Integrated design of downwind land‐based wind turbines using analytic gradients

Ning

Petch

2016

Wind Energy

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Wind turbines are complex systems where component‐level changes can have significant system‐level effects. Effective wind turbine optimization generally requires an integrated analysis approach with a large number of design variables. Optimizing across large variable sets is orders of magnitude more efficient with gradient‐based methods as compared with gradient‐free method, particularly when using exact gradients. We have developed a wind turbine analysis set of over 100 components where 90% of the models provide numerically exact gradients through symbolic differentiation, automatic differentiation, and adjoint methods. This framework is applied to a specific design study focused on downwind land‐based wind turbines. Downwind machines are of potential interest for large wind turbines where the blades are often constrained by the stiffness required to prevent a tower strike. The mass of these rotor blades may be reduced by utilizing a downwind configuration where the constraints on tower strike are less restrictive. The large turbines of this study range in power rating from 5–7MW and in diameter from 105m to 175m. The changes in blade mass and power production have important effects on the rest of the system, and thus the nacelle and tower systems are also optimized. For high‐speed wind sites, downwind configurations do not appear advantageous. The decrease in blade mass (10%) is offset by increases in tower mass caused by the bending moment from the rotor‐nacelle‐assembly. For low‐wind speed sites, the decrease in blade mass is more significant (25–30%) and shows potential for modest decreases in overall cost of energy (around 1–2%). Copyright © 2016 John Wiley & Sons, Ltd.

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The simultaneous effect of a fairing tower and increased blade flexibility on a downwind mounted rotor

Cited by 15 publications

References 10 publications

Analytic analysis of load alignment for coning extreme‐scale rotors

Analytic analysis of load alignment for coning extreme‐scale rotors

Multidisciplinary design optimization of large wind turbines—Technical, economic, and design challenges

Integrated design of downwind land‐based wind turbines using analytic gradients

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