Preprints
https://doi.org/10.5194/wes-2020-43
https://doi.org/10.5194/wes-2020-43
12 Feb 2020
 | 12 Feb 2020
Status: this preprint was under review for the journal WES but the revision was not accepted.

Accurate loads and velocities on low solidity wind turbines using an improved Blade Element Momentum model

Yassine Ouakki and Abdelaziz Arbaoui

Abstract. The accurate prediction of loadings and velocities on a wind turbine blades is essential for the design and optimization of wind turbines rotors. However, the classical BEM still suffer from an inaccurate prediction of induced velocities and loadings, even if the classical correction like stall delay effect and tip loss correction are used. For low solidity rotors, the loadings are generally over-predicted in the tip region, since the far wake expansion is not accurately accounted for in the one-dimensional (1D) momentum theory. The 1D dimensional momentum theory supposes that the far wake axial induction is equal to twice the axial induction in the rotor plane, which results in an under-estimation of the axial induction factor in the tip region. Considering the complex nature of the flow around a rotating blade, the accurate estimation of 3D effects is still challenging, since most stall delay models still often tend to under-predict or over-predict the loadings near the root region. As for the solution method for the classical BEM equation, the induced velocities are computed accounting for the drag force. However, according to the Kutta-Joukowski theorem, the induced velocities on a blade element are only created by lift force. Accounting for drag force when solving the BEM will result in an over-estimation of the axial induction factor, while the tangential induction factor is under-estimated. To improve the accuracy of the BEM method, in this paper, the 1D momentum theory is corrected using a new far wake expansion model to take into account the radial flow effect. The blade element theory is corrected for three-dimensional effects through an improved stall delay model. An improved solution method for the BEM equations respecting the Kutta-Joukowski theorem is proposed. The improved BEM model is used to estimate the aerodynamic loads and velocities on the National Renewable Energy Laboratory Phase VI rotor blades. The results of this study show that the proposed BEM model gives an accurate prediction of the loads and velocities compared to the classical BEM model.

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Yassine Ouakki and Abdelaziz Arbaoui
 
Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement
Yassine Ouakki and Abdelaziz Arbaoui
Yassine Ouakki and Abdelaziz Arbaoui

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Short summary
It is well known that the classical BEM model fails to accurately predict the loadings and velocities on a wind turbines blade. In this work, an improved BEM model for low solidity wind turbines is proposed by accounting for 3D stall delay and far wake expansion effects. Additionally, the improved BEM equations are solved without the drag force. The results show that the improved BEM model predicts accurately the loading and velocities on the NREL phase VI rotor compared to the classical BEM.
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