Is the Blade Element Momentum theory overestimating wind turbine loads? – An aeroelastic comparison between OpenFAST's AeroDyn and QBlade's Lifting-Line Free Vortex Wake method

Perez‐Becker, Sebastian; Papi, Francesco; Saverin, Joseph; Marten, David; Bianchini, Alessandro; Paschereit, Christian Oliver

doi:10.5194/wes-5-721-2020

Cited by 31 publications

(21 citation statements)

References 26 publications

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“…Vortex methods can model the wake with far fewer assumptions and engineering corrections compared to BEM methods. Especially when the wind turbine is subjected to unsteady inflow or varying blade loads, the LLFVW method increases the accuracy compared to BEM methods (Perez-Becker et al, 2020). To model the dynamic stall of the blade elements, QBlade uses the ATE-Flap unsteady aerodynamic model (Bergami and Gaunaa, 2012), modified so that it excludes contribution of the wake in the attached flow region (Wendler et al, 2016).…”

Section: Qbladementioning

confidence: 99%

“…A more detailed comparison between QBlade and (Open)FAST can be found in Perez-Becker et al (2020).…”

Section: Qbladementioning

confidence: 99%

“…Although the number of simulations is rather low to determine the overall extreme values of M BR XY and D T2T X , our selection will give us a good estimate of their maxima. By using QBlade -which has the lifting line free vortex wake (LLFVW) aerodynamic model and a multi-body based structural model -we ensure that the results of our load calculations are more accurate than with other codes that use the more common BEM aerodynamic model (Perez-Becker et al, 2020). In all simulations we included additional 100 s simulation time to allow the wake to develop.…”

Section: Simulation Setupmentioning

confidence: 99%

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Active flap control with the trailing edge flap hinge moment as a sensor: using it to estimate local blade inflow conditions and to reduce extreme blade loads and deflections

2021

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Abstract. Active trailing edge flaps are a promising technology that can potentially enable further increases in wind turbine sizes without the disproportionate increase in loads, thus reducing the cost of wind energy even further. Extreme loads and critical deflections of the blade are design-driving issues that can effectively be reduced by flaps. In this paper, we consider the flap hinge moment as a local input sensor for a simple flap controller that reduces extreme loads and critical deflections of the DTU 10 MW Reference Wind Turbine blade. We present a model to calculate the unsteady flap hinge moment that can be used in aeroelastic simulations in the time domain. This model is used to develop an observer that estimates the local angle of attack and relative wind velocity of a blade section based on local sensor information including the flap hinge moment of the blade section. For steady wind conditions that include yawed inflow and wind shear, the observer is able to estimate the local inflow conditions with errors in the mean angle of attack below 0.2∘ and mean relative wind speed errors below 0.4 %. For fully turbulent wind conditions, the observer is able to estimate the low-frequency content of the local angle of attack and relative velocity even when it is lacking information on the incoming turbulent wind. We include this observer as part of a simple flap controller to reduce extreme loads and critical deflections of the blade. The flap controller's performance is tested in load simulations of the reference turbine with active flaps according to the IEC 61400-1 power production with extreme turbulence group. We used the lifting line free vortex wake method to calculate the aerodynamic loads. Results show a reduction of the maximum out-of-plane and resulting blade root bending moments of 8 % and 7.6 %, respectively, when compared to a baseline case without flaps. The critical blade tip deflection is reduced by 7.1 %. Furthermore, a sector load analysis considering extreme loading in all load directions shows a reduction of the extreme resulting bending moment in an angular region covering 30∘ around the positive out-of-plane blade root bending moment. Further analysis reveals that a fast reaction time of the flap system proves to be critical for its performance. This is achieved with the use of local sensors as input for the flap controller. A larger reduction potential of the system is identified but not reached mainly because of a combination of challenging controller objectives and the simple controller architecture.

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Section: Qbladementioning

confidence: 99%

“…A more detailed comparison between QBlade and (Open)FAST can be found in Perez-Becker et al (2020).…”

Section: Qbladementioning

confidence: 99%

Section: Simulation Setupmentioning

confidence: 99%

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Active flap control with the trailing edge flap hinge moment as a sensor: using it to estimate local blade inflow conditions and to reduce extreme blade loads and deflections

2021

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“…Recently Perez-Becker et al (2020) and Boorsma et al (2020) compared aeroelastic simulations based on Blade Element Momentum (BEM) theory and Free Vortex Wake Methods (FVWM). In addition to the need of engineering models for dynamic inflow effects, BEM is based on the assumption of axial and uniform inflow.…”

Section: Introductionmentioning

confidence: 99%

Experimental analysis of the dynamic inflow effect due to coherent gusts

Berger¹,

Neuhaus²,

Onnen³

et al. 2022

Preprint

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Abstract. The dynamic inflow effect describes the unsteady aerodynamic response to fast changes in rotor loading, due to the inertia of the wake. For pitch actuation and fast rotor speed changes this effect leads to load overshoots. The effect is suspected to be also relevant for gust situations, however this was never shown. The objective of the paper is to proove the dynamic inflow effect due to gusts and compare dynamic inflow engineering models to corresponding measurements. A 1.8 m diameter model turbine is used in the large wind tunnel of ForWind – University of Oldenburg with an active grid to impress rotor uniform gusts on the flow. The campaign features load and velocity measurements of the axial flow in the rotor plane. The unsteady dynamic inflow effect is investigated by comparing two experimental cases. Firstly, a dynamic measurement during a gust situation is performed. Secondly, quasi-steady loads and axial velocities are interpolated from a steady characterisation experiment according to the gust wind speed. By comparing both cases, the influence attributed to the dynamic inflow effect is isolated. Further comparisons to a typical Blade Element Momentum code and a higher fidelity Free VortexWake Model are performed. Based on analytical considerations an improvemed formulation of the Øye dynamic inflow model is proposed. The experiment shows a dynamic inflow effect due to gusts in the loads and axial velocity measurements. It leads to a reduction in load and axial velocity amplitudes and consequently also lower fatigue loading. The higher fidelity model shows a similar impact of the dynamic inflow effect. In contrast, the commonly used Øye engineering model in the BEM code predicts an increase in load amplitude and thus higher fatigue loads. The improved Øye engineering model however catches the observed dynamic inflow effect due to gusts in accordance to the experiment and FVWM simulations. An amplification of induced velocities, seen in the experiment and FVWM simulation, causes the reduced load amplitudes. Therefore, classic dynamic inflow models, which filter the induced velocity, cannot predict the effect. The proposed improvement to additionally consider the wake velocity for the filter of the dynamic inflow engineering model, proves to be a straight forward but also effective modification. In conclusion, these new experimental findings on dynamic inflow due to gusts and improvements to the Øye model enable improvements in wind turbine design by catching the related lower fatigue loads.

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“…CFD applications with arbitrary motions are still challenging and not readily available. Vorticity-based methods have long been considered as the intermediate solution between the computationally intensive CFD methods and the engineering models such as BEM (Perez-Becker et al, 2020;Boorsma et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

A multi-purpose lifting-line flow solver for arbitrary wind energy concepts

Branlard

Brownstein²,

Strom³

et al. 2021

Preprint

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Abstract. In this work, we extend the AeroDyn module of OpenFAST to be able to support arbitrary collections of wings, rotors and towers. The new standalone AeroDyn driver supports arbitrary motions of the lifting-surfaces and complex turbulent inflows. We describe the features and updates necessary for the implementation of the new AeroDyn driver. We present different case studies of the driver to illustrate its application to concepts such as: multi-rotors, kites, or vertical axis wind turbines. We perform verification and validation of some of the new features using the following test cases: an elliptical wing, a horizontal axis wind turbine, and a 2D and 3D vertical axis wind turbines. The wind turbine simulations are compared to field measurements. We use this opportunity to point out some limitations of current models and highlight areas which we think should be the focus of future research in wind turbine aerodynamics.

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Is the Blade Element Momentum theory overestimating wind turbine loads? – An aeroelastic comparison between OpenFAST's AeroDyn and QBlade's Lifting-Line Free Vortex Wake method

Cited by 31 publications

References 26 publications

Active flap control with the trailing edge flap hinge moment as a sensor: using it to estimate local blade inflow conditions and to reduce extreme blade loads and deflections

Active flap control with the trailing edge flap hinge moment as a sensor: using it to estimate local blade inflow conditions and to reduce extreme blade loads and deflections

Experimental analysis of the dynamic inflow effect due to coherent gusts

A multi-purpose lifting-line flow solver for arbitrary wind energy concepts

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