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.

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The quest for reduced levelized cost of energy has driven significant growth in wind turbine size; however, larger rotors face significant technical and logistical challenges. The largest published rotor design is 25 MW, and here we consider an even larger 50 MW design with blade length over 250 m. This paper shows that a 50 MW design is indeed possible from a detailed engineering perspective and presents a series of aero-structural blade designs, and critical assessment of technology pathways and challenges for extreme-scale rotors. The 50 MW rotor design begins with Monte Carlo simulations focused on optimizing carbon spar cap and root design. A baseline design resulted in a 250-m blade with mass of 502 tonnes. Subsequently, an aero-structural design and optimization were performed to reduce the blade mass/cost with more than 25% mass reduction and 30% cost reduction by determining optimal blade chord and airfoil thickness for best aero-structural performance.

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.

A 105‐m, 13‐MW two‐bladed downwind Segmented Ultralight Morphing Rotor (SUMR‐13) blade was gravo‐aeroelastically scaled by 20% to a 20.87‐m‐long demonstrator blade and confirmed through structural ground testing. The subscale model was achieved through geometric scaling and by aeroelastic scaling principles based on operational flapwise deflections combined with rotational and structural frequencies while retaining the turbine tip‐speed ratio. In particular, the subscale demonstrator was designed to replicate, as closely as possible, the nondimensional geometry, the ratio of centrifugal to gravitational moments, the tip‐speed ratio, and the nondimensional rotation rate. The intent for this demonstrator was to achieve the same nondimensional flapwise blade deflections and dynamics of the full‐scale 13‐MW rotor. The manufactured SUMR‐D blade resulted in less than half of the mass of the conventional two‐bladed Controls Advanced Research Turbine (CART2) rotor blade based on scaling and a lower power rating, though with some differences in mass and stiffness from the ideal scaled‐down design to meet safety requirements at the test site. To achieve proper scaling, operational pitch control set points were altered to account for the differences by evaluating simulated operation of both the SUMR‐13 and SUMR‐D rotors. Structural testing of the SUMR‐D blade investigated the response to well‐defined flapwise loads and indicated that the subscale blade had the appropriate elastic properties needed for both scaling and for safe operational field testing.

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