Free-Tip Rotor Wind Tunnel Test Results

Stroub, Robert H.; Young, Larry A.; Keys, Charles N.; Cawthorne, Matthew H.

doi:10.4050/jahs.31.19

Cited by 3 publications

(3 citation statements)

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“…The passive tip concept was also validated through experiments (Stroub, 1985), which confirmed a considerable reduction in required power in high thrust conditions. This result is related to a favorable influence of the blade tip negative pitch angle with respect to the inboard blade portion.…”

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confidence: 79%

Articulated blade tip devices for load alleviation on wind turbines

Bottasso¹,

Croce²,

Gualdoni³

et al. 2016

Preprint

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Abstract. This paper investigates the load alleviation capabilities of an articulated tip device, where the outermost portion of the blade can rotate with respect to the rest of the blade. Passive, semi-passive and active solutions are developed for the tip rotation. In the passive and semi-passive configurations tip pitching is mainly driven by aerodynamic loads, while for the active case the rotation is obtained with an actuator commanded by a feedback control law. Each configuration is analyzed and tested using a high-fidelity aeroservoelastic simulation environment, by considering standard operative conditions as well as fault situations. The potential benefits of the proposed blade tip concepts are discussed in terms of performance and robustness.

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mentioning

confidence: 79%

Articulated blade tip devices for load alleviation on wind turbines

Bottasso¹,

Croce²,

Gualdoni³

et al. 2016

Preprint

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“…Since the mean relative rotation of the tip is related to the restraining moment at the hinge, a preload was used as a tuning parameter to modulate the blade tip angle of attack and the resulting aerodynamic forces. 20 The passive tip concept was also validated through experiments (Stroub, 1985), which confirmed a considerable reduction in required power in high thrust conditions. This result is related to a favorable influence of the blade tip negative pitch angle with respect to the inboard blade portion.…”

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confidence: 79%

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Bottasso¹

2016

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This paper investigates the load alleviation capabilities of an articulated tip device, where the outermost portion of the blade can rotate with respect to the rest of the blade. Passive, semi-passive and active solutions are developed for the tip rotation. In the passive and semi-passive configurations tip pitching is mainly driven by aerodynamic loads, while for the active case the rotation is obtained with an actuator commanded by a feedback control law. Each configuration is analyzed and tested using a high-fidelity aeroservoelastic simulation environment, by considering standard operative conditions as well as fault 5 situations. The potential benefits of the proposed blade tip concepts are discussed in terms of performance and robustness. Introduction and motivationThe cost of energy (CoE) is the key parameter that determines the success of an energy source. In recent years, both industry and the wind energy scientific community have focused their efforts on the reduction of the CoE, with the goal of increasing the competitiveness of energy from wind with respect to other technologies. A reduction in the CoE can be obtained by a variety 10 of means, one of the most significant effects coming from an increase in the annual energy production (AEP). AEP can be increased by improving the aerodynamic efficiency of the rotor and by harvesting a greater amount of energy with larger swept areas and taller towers. Because of this, together with other scale benefits typically associated with larger wind turbines, there is a very clear marked trend towards bigger machines. In the offshore case, where logistics and transportation are very different than onshore, the trend towards very large wind turbines is even clearer, the optimum plateaux not having been reached yet. 15To satisfy this growth trend, the simple upscaling of existing machines is unfeasible. In fact, as cost is typically well correlated with mass and mass with volume, a naive scaling would translate into an unacceptable cubic growth of cost. Among other approaches, load alleviation techniques help address this issue, increasing the efficiency of the aerostructural configuration and limiting the cost grow rate of wind turbine components (Thresher, 2008).The mitigation of loads can be obtained by full-span/distributed and passive/active solutions. Full-span solutions involve the 20 response of the entire blade. Individual pitch control (IPC) is a full-span active technique, which is seeing an ever increasing acceptance by industry, while bend-twist coupling (BTC) is an example of the full-span passive category .Although often very effective, any full-span solution is inherently somewhat limited in bandwidth, due to the inertia and non-1 Wind Energ. Sci. Discuss., doi:10.5194/wes-

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“…In essence, the active tip is an extension of the free-tip and constant-lift rotor concept. Chopra [31] analytically demonstrated the aeroelastic benefits of these rotor systems and Stroub [32] demonstrated power reduction of 12% in windtunnel tests of a free tip (at an advance ratio of 0.3). In addition, the oscillatory flapwise bending moments and pitch-link loads were reduced (albeit with a simultaneous increase in in-plane bending moments).…”

Section: Introductionmentioning

confidence: 99%

Analysis of a bending-torsion coupled actuator for a smart rotor with active blade tips

Bernhard

Chopra

2001

Smart Mater. Struct.

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Active rotorblade tips offer an alternative approach to the challenge of main rotor active vibration control. The tips are pitched with respect to the main blade via a piezo-driven bending-torsion coupled actuator beam that runs down the length of the blade. A Vlasov based, specialized one-dimensional finite beam element is developed to model the rotating actuator beam and is validated with the free-vibration and static forced response of 4:1 and 2:1 aspect ratio, bending-torsion coupled, active and passive plates. A one-eighth scale, reduced tip-speed rotor model (tip Mach 0.26), incorporating the bending-torsion actuator beam, has been previously hover tested (open loop). In these tests, blade tip deflections of the order of 2 • (half peak-to-peak) were achieved at 2, 3, 4, 5/rev with corresponding dynamic vertical blade root shear variations of the order of 10-20% of the nominal blade lift at 8 • collective (C T /σ = 0.07). The test results are used to validate a coupled actuator and elastic rotorblade model. The correlation of the predicted active blade-tip pitch deflections and the experimental data is within 20%. The predicted values for the active vertical root shears are within the same margin for 4 • and 6 • collective. Nomenclature A, B, D classical lamination stiffness matrices c chord c E ij elastic stiffness matrix, at constant electric field D i electric displacement, C m −2 d ij piezo constants, m V −1 = C N −1 e ij piezo constants, C m −2 , e ij = d ik c E kj

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Free-Tip Rotor Wind Tunnel Test Results

Cited by 3 publications

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Articulated blade tip devices for load alleviation on wind turbines

Articulated blade tip devices for load alleviation on wind turbines

Reply to reviewers

Analysis of a bending-torsion coupled actuator for a smart rotor with active blade tips

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