Abstract
As part of the AVATAR and Mexnext projects, this study compares several methods used to derive lifting line variables from CFD simulations of the MEXICO rotor in yawed inflow. The results from six partners within the AVATAR/Mexnext consortium using five different methods of extraction were compared. Overall comparison of the induced velocities at the mid and tip parts of blade shows fairly good agreement between the tested methods, where the derived angle of attack differs within 1°, within the linear range this accounts to ˂ 10% uncertainty on the aerodynamic forces. The presented comparison shows inadequate agreement between the methods for application towards the root.
Highlights
The calculation of a wind turbine design load spectrum is very time consuming [1] and requires the application of a low fidelity aerodynamic model based on the blade element momentum(BEM) method
The 3−Point method introduced by Rahimi et al [22, 2] denoted with 3P was tested in this benchmark study. This method is based on the average azimuthal technique (AAT) [23][24], it uses only three points along the chord length on each side of the blade section to perform the averaging of the velocities and extract the angle of attack (AoA) (Figure 3)
Unlike the AAT method, this method is able to reproduce the dynamic behavior of the induction and AoA for each azimuthal position and near the tip and root of the blade which is very important for the yawed flow
Summary
The calculation of a wind turbine design load spectrum is very time consuming [1] and requires the application of a low fidelity aerodynamic model based on the blade element momentum(BEM) method. The 3−Point method introduced by Rahimi et al [22, 2] denoted with 3P was tested in this benchmark study This method is based on the average azimuthal technique (AAT) [23][24], it uses only three points along the chord length on each side of the blade section to perform the averaging of the velocities and extract the AoA (Figure 3). Unlike the AAT method, this method is able to reproduce the dynamic behavior of the induction and AoA (local induced velocity and AoA) for each azimuthal position and near the tip and root of the blade which is very important for the yawed flow This has been shown in previous works with a comparison to a lifting line free vortex wake code [22]. Other methods, like e.g. Upwash are preferred
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