Bend-twist coupling potential of wind turbine blades

Fedorov, V. I.; Berggreen, Christian

doi:10.1088/1742-6596/524/1/012035

Cited by 35 publications

(39 citation statements)

References 8 publications

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“…Fedorov (2012) presents a numerical and experimental approach where the effects of loads on a composite bend-twist full-scale wind turbine blade are measured. In particular they measured deflection and twist using Digital Image Correlation (DIC), however the uncertainty is not stated.…”

Section: Introductionmentioning

confidence: 99%

Uncertainty assessment of coupled Digital Image Correlation and Particle Image Velocimetry for fluid-structure interaction wind tunnel experiments

Giovannetti

Banks

Turnock

et al. 2017

Journal of Fluids and Structures

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The development of advanced composite structures for maritime and aerospace applications requires the ability to quantify their actual performance under known fluid loads. One example is the need to investigate the differences in fluid-structure response of passive adaptive composite structures. A wind tunnel based method is used to quantify the structural behaviour, and fluid response, of a flexible aerofoil under fluid loading. The technique measures the deflection of the structure, with high speed stereoscopic Digital Image Correlation (DIC). The tip vortex position is measured using high resolution stereoscopic Particle Image Velocimetry (PIV). The accuracy of the two full-field optical measurement systems is quantified and the effect of optical interactions is assessed. A flexible NACA0015 rectangular plan-form aerofoil of 0.9 m span and aspect ratio of two is subjected to aerodynamic loading within a closed circuit wind tunnel. The wind speed was varied from 10 to 25 m/s within a 3.5 m x 2.4 m working section. The structural response is measured simultaneously with the fluid flow field around the tip vortex. The tip vortex core, which moved by ≈ 62 mm at the highest wind speed, is directly compared to the deformation of the structure, which deflected by ≈ 58mm. A maximum foil twist of ≈ 0.6 deg was observed. The DIC accuracy is evaluated in static and transient conditions for translational and rotational movement. The DIC maximum error for translations, greater than or equal to 0.5 mm, is less than 3% and less than 0.6% in dynamic motions. The DIC total error for rotations is less than 5% in static motions and 1% in Email address: L.Marimon-Giovannetti@soton.ac.uk (L. Marimon Giovannetti) Preprint submitted to Journal of Fluids and StructuresOctober 21, 2016 dynamic rotations. The PIV uncertainty is quantified a posteriori providing the errors due to the correlation algorithm and the experimental setup. The mean in-plane velocity component uncertainties in the vortex region varied between 1.2% and 3.5% depending on flow speed (≈ 0.1 px) around the vortex structure. The mean out-of-plane velocity uncertainty around the vortex varies between 2% and 3.3% depending on flow speed.

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Section: Introductionmentioning

confidence: 99%

Uncertainty assessment of coupled Digital Image Correlation and Particle Image Velocimetry for fluid-structure interaction wind tunnel experiments

Giovannetti

Banks

Turnock

et al. 2017

Journal of Fluids and Structures

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“…Composite materials not only present a high stiffness to weight ratio, but also a better fatigue resistance compared to metallic components . Using the anisotropy of the material, it is possible to design components presenting elastic couplings that will enhance the performance of the whole structure (Veers and Bir 1998, V. Fedorov 2012, Shirk and Hertz 1986, Liu and Young 2009, Young 2008. Careful directional placement of fibres and design of the composite architecture can result in an additional coupled response that will affect the effective angle of attack of the foil structures.…”

Section: Introductionmentioning

confidence: 99%

Assessment of Digital Image Correlation as a method of obtaining deformations of a structure under fluid load

Banks

Giovannetti

Soubeyran

et al. 2015

Journal of Fluids and Structures

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Digital Image Correlation (DIC) is employed for the measurement of full-field deformation during fluid-structure interaction experiments in a wind tunnel. The methodology developed for the wind tunnel environment is quantitatively assessed. The static deformation error of the system is shown to be less than 0.8% when applied to a curved aerofoil specimen moved through known displacements using a micrometer. Enclosed camera fairings were shown to be required to minimise error due to wind induced camera vibration under aerodynamic loading. The methodology was demonstrated using a high performance curved foil, from a NACRA F20 sailing catamaran, tested within the University of Southampton RJ Mitchell, 3.5m x 2.4m, wind tunnel. The aerodynamic forces induced in the wind tunnel are relatively small, compared with typical hydrodynamic loading, resulting in small deformations. The coupled deflection and blade twist is evaluated over the tip region (80-100% Span, measured from the root) for a range of wind speeds and angles of attack. Steady deformations at low angles of attack were shown to be well captured however unsteady deformations at higher angles of attack were observed as an increase in variability due to hardware limitations in the current DIC system. It is concluded that higher DIC sample rates are required to assess unsteady deformations in the future. The full field deformation data reveals limited blade twist for low angles of attack, below the stall angle. For larger angles, however, there is a tendency to reduce the effective angle of attack at the tip of the structure, combined with an unsteady structural response. This capability highlights the benefits of the presented methodology over fixed-point measurements as the three dimensional foil deflections can be assessed over a large tip region. In addition, the methodology demonstrates that very small deformations and twist angles can be resolved.

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“…For a positive definite stiffness matrix the coupling coefficients have to be |γ x/y | < 1. For wind turbine blades values up to 0.2-0.4 are deemed achievable (Capellaro and Kühn, 2010;Fedorov and Berggreen, 2014). Negative coupling coefficients result in pitch to feather (reducing the angle of attack) for edgewise/flapwise deflection towards the leading edge/suction side of the blade.…”

Section: Validationmentioning

confidence: 99%

Modal properties and stability of bend–twist coupled wind turbine blades

2017

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Abstract.Coupling between bending and twist has a significant influence on the aeroelastic response of wind turbine blades. The coupling can arise from the blade geometry (e.g. sweep, prebending, or deflection under load) or from the anisotropic properties of the blade material. Bend-twist coupling can be utilized to reduce the fatigue loads of wind turbine blades. In this study the effects of material-based coupling on the aeroelastic modal properties and stability limits of the DTU 10 MW Reference Wind Turbine are investigated. The modal properties are determined by means of eigenvalue analysis around a steady-state equilibrium using the aero-servo-elastic tool HAWCStab2 which has been extended by a beam element that allows for fully coupled cross-sectional properties. Bend-twist coupling is introduced in the cross-sectional stiffness matrix by means of coupling coefficients that introduce twist for flapwise (flap-twist coupling) or edgewise (edge-twist coupling) bending. Edge-twist coupling can increase or decrease the damping of the edgewise mode relative to the reference blade, depending on the operational condition of the turbine. Edge-twist to feather coupling for edgewise deflection towards the leading edge reduces the inflow speed at which the blade becomes unstable. Flap-twist to feather coupling for flapwise deflections towards the suction side increase the frequency and reduce damping of the flapwise mode. Flap-twist to stall reduces frequency and increases damping. The reduction of blade root flapwise and tower bottom fore-aft moments due to variations in mean wind speed of a flap-twist to feather blade are confirmed by frequency response functions.

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Bend-twist coupling potential of wind turbine blades

Cited by 35 publications

References 8 publications

Uncertainty assessment of coupled Digital Image Correlation and Particle Image Velocimetry for fluid-structure interaction wind tunnel experiments

Uncertainty assessment of coupled Digital Image Correlation and Particle Image Velocimetry for fluid-structure interaction wind tunnel experiments

Assessment of Digital Image Correlation as a method of obtaining deformations of a structure under fluid load

Modal properties and stability of bend–twist coupled wind turbine blades

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