Investigation of Innovative Rotor Concepts for the Big Adaptive Rotor Project

Johnson, Nick; Bortolotti, Pietro; Dykes, Katherine; Barter, Garrett; Moriarty, Patrick; Carron, William Scott; Wendt, Fabian; Veers, Paul S.; Paquette, Joshua; Kelly, Christopher B.; Ennis, Brandon Lee

doi:10.2172/1563139

Cited by 20 publications

(19 citation statements)

References 28 publications

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“…To date, the wind industry has been able to avoid uneconomical scaling-related cost increases by streamlining manufacturing operations, optimizing turbine design, and using fewer, lighter, and stronger materials Rønde 2011a, 2011b;Razdan and Garrett 2018a, 2018b, 2015a, 2015bWiser et al 2011). Figure 7 employs mass data sourced from Vestas' life-cycle analyses of its 2.0 MW platform in order to plot how mass intensity (expressed three ways, from left to right: in kg/kW, kg/m 2 of swept area, and kg/MWh) has changed with specific power over time.…”

Section: Subtask 1a: Trends Analysis For Lower-specific-power Wind Turbinesmentioning

confidence: 99%

“…Phase I of the project focused on identifying technology to overcome the transportation and operational limitations for a 5-MW wind turbine with a 206-m rotor and developed promising designs incorporating lightweight and flexible structures that are less expensive and more reliable than current segmented-blade approaches. The BAR team investigated several innovative 100-m blade technologies (Johnson et al 2019), and the most promising BAR concepts were found to be (1) highly flexible, controlled bending blades for rail transport, (2) downwind rotors to accommodate the highly flexible blades without the risk of a tower strike, and (3) distributed aerodynamic control (DAC) devices to control the load on the highly flexible blades. In Phase I, the team also identified several science and engineering challenges and areas of focus to accelerate the advancement of the BAR concepts.…”

Section: Introductionmentioning

confidence: 99%

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Big Adaptive Rotor Phase I Final Report

Johnson¹,

Paquette²,

Bortolotti³

et al. 2021

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This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.3. Completed research-and-development opportunity screening 4. Performed model improvements and detailed design studies 5. Assessed low-cost carbon fiber.The remainder of this report focuses on the findings from each task and includes excerpts and citations from previously published work.

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Section: Subtask 1a: Trends Analysis For Lower-specific-power Wind Turbinesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Big Adaptive Rotor Phase I Final Report

Johnson¹,

Paquette²,

Bortolotti³

et al. 2021

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“…The project used a 5 MW, 206 m rotor as a reference turbine platform to examine the limits of current design tools and methodologies. After an initial study and down-select of turbine innovations (Johnson et al, 2019), the concept of slender flexible blades that can be transported by train via controlled flapwise bending (Carron and Bortolotti, 2020) was chosen as the primary concept to be evaluated. Three enabling technologies were selected as having high potential to enable this concept: downwind rotors, carbon fiber, and distributed aerodynamic controls.…”

Section: Introductionmentioning

confidence: 99%

Land-based wind turbines with flexible rail transportable blades – Part II: 3D FEM design optimization of the rotor blades

Camarena

Anderson

Paquette

et al. 2021

Preprint

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Abstract. Increasing growth in land-based wind turbine blades to enable higher machine capacities and capacity factors is creating challenges in design, manufacturing, logistics, and operation. Enabling further blade growth will require technology innovation. An emerging solution to overcome logistics constraints is to segment the blades spanwise and chordwise, which is effective, but the additional field-assembled joints result in added mass and loads, as well as increased reliability concerns in operation. An alternative to this methodology is to design slender flexible blades that can be shipped on rail lines by flexing during transport. However, the increased flexibility is challenging to accommodate with a typical glass-fiber, upwind design. In a two-part paper series, several design options are evaluated to enable slender flexible blades: downwind machines, optimized carbon fiber, and active aerodynamic controls. Part 1 presents the system-level optimization of the rotor variants as compared to conventional and segmented baselines, with a low-fidelity representation of the blades. The present work, Part 2, supplements the system-level optimization in Part 1 with high-fidelity blade structural optimization to ensure that the designs are at feasible optima with respect to material strength and fatigue limits, as well as global stability and structural dynamics constraints. To accommodate the requirements of the design process, a new version of the Numerical Manufacturing And Design (NuMAD) code has been developed and released. The code now supports laminate-level blade optimization and an interface to the International Energy Agency Wind Task 37 blade ontology. Transporting long, flexible blades via controlled flapwise bending is found to be a viable approach for blades up to 100 m. The results confirm that blade mass can be substantially reduced by going either to a downwind design or to a highly coned and tilted upwind design. A discussion of active and inactive constraints consisting of material rupture, fatigue damage, buckling, deflection, and resonant frequencies is presented. An analysis of driving load cases revealed that the downwind designs are dominated by loads from sudden, abrupt events like gusts rather than fatigue. Finally, an analysis of carbon fiber spar caps for downwind machines finds that, compared to typical carbon fibers, the use of a new heavy-tow carbon fiber in the spar caps is found to yield between 9 % and 13 % cost savings.

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“…The primary motivation for the low-induction concept is to lower the cost of energy in scenarios where sacrificing some power in reducing design induction values leads to relatively more significant load reductions that are of overall economic benefit to the design. Discussion of the low-induction concept appears in Johnson (2019), where Christopher L. Kelly of Sandia National Laboratories, in an unpublished presentation at the Wind Energy Science Conference of 2017, had noted that the first low-induction design with constrained blade rotor bending moment was due to Ludwig Prandtl and is reproduced in Tollmien et al (1961). Snel (2003) observed that when the power coefficient, C p , is stationary at its maximum value associated with an axial induction of 1/3, the thrust coefficient, C t , is still strongly increasing.…”

Section: Introductionmentioning

confidence: 99%

Top-level rotor optimisations based on actuator disc theory

Jamieson

2020

Wind Energ. Sci.

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Abstract. Ahead of the elaborate rotor optimisation modelling that would support detailed design, it is shown that significant insight and new design directions can be indicated with simple, high-level analyses based on actuator disc theory. The basic equations derived from actuator disc theory for rotor power, axial thrust and out-of-plane bending moment in any given wind condition involve essentially only the rotor radius, R, and the axial induction factor, a. Radius, bending moment or thrust may be constrained or fixed, with quite different rotor optimisations resulting in each case. The case of fixed radius or rotor diameter leads to conventional rotor design and the long-established result that power is maximised with an axial induction factor, a=1/3. When the out-of-plane bending moment is constrained to a fixed value with axial induction variable in value (but constant radially) and when rotor radius is also variable, an optimum axial induction of 1∕5 is determined. This leads to a rotor that is expanded in diameter 11.6 %, gaining 7.6 % in power and with thrust reduced by 10 %. This is the low-induction rotor which has been investigated by Chaviaropoulos and Voutsinas (2013). However, with an optimum radially varying distribution of axial induction, the same 7.6 % power gain can be obtained with only 6.7 % expansion in rotor diameter. When without constraint on bending moment, the thrust is constrained to a fixed value, and the power is maximised as a→0, which for finite power extraction would require R→∞. This result is relevant when secondary rotors are used for power extraction from a primary rotor. To avoid too much loss of the source power available from the primary rotor, the secondary rotors must operate at very low induction factors whilst avoiding too high a tip speed or an excessive rotor diameter. Some general design issues of secondary rotors are explored. It is suggested that they may have the most practical potential for large vertical axis turbines avoiding the severe penalties on drivetrain cost and weight implicit in the usual method of power extraction from a central shaft.

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Investigation of Innovative Rotor Concepts for the Big Adaptive Rotor Project

Abstract: Department of Energy (DOE) reports produced after 1991 and a growing number of pre-1991 documents are available free via www.OSTI.gov.

Cited by 20 publications

References 28 publications

Big Adaptive Rotor Phase I Final Report

Big Adaptive Rotor Phase I Final Report

Land-based wind turbines with flexible rail transportable blades – Part II: 3D FEM design optimization of the rotor blades

Top-level rotor optimisations based on actuator disc theory

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