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Title: Modeling Wind Turbine Tower and Nacelle Effects within an Actuator Line Model

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National Renewable Energy Lab. (NREL), Golden, CO (United States)
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Conference: AIAA SciTech: 33rd Wind Energy Symposium, 5-9 January 2015, Kissimmee, Florida
Country of Publication:
United States
17 WIND ENERGY; wind power; wind turbine; nacelle

Citation Formats

Churchfield, Matthew J., Wang, Zhixiang, and Schmitz, Sven. Modeling Wind Turbine Tower and Nacelle Effects within an Actuator Line Model. United States: N. p., 2015. Web. doi:10.2514/6.2015-0214.
Churchfield, Matthew J., Wang, Zhixiang, & Schmitz, Sven. Modeling Wind Turbine Tower and Nacelle Effects within an Actuator Line Model. United States. doi:10.2514/6.2015-0214.
Churchfield, Matthew J., Wang, Zhixiang, and Schmitz, Sven. 2015. "Modeling Wind Turbine Tower and Nacelle Effects within an Actuator Line Model". United States. doi:10.2514/6.2015-0214.
title = {Modeling Wind Turbine Tower and Nacelle Effects within an Actuator Line Model},
author = {Churchfield, Matthew J. and Wang, Zhixiang and Schmitz, Sven},
abstractNote = {},
doi = {10.2514/6.2015-0214},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2015,
month = 1

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  • The current actuator line method (ALM) within an OpenFOAM computational fluid dynamics (CFD) solver was used to perform simulations of the NREL Phase VI rotor under rotating and parked conditions, two fixed-wing designs both with an elliptic spanwise loading, and the NREL 5-MW turbine. The objective of this work is to assess and improve the accuracy of the state-of-the-art ALM in predicting rotor blade loads, particularly by focusing on the method used to project the actuator forces onto the flow field as body forces. Results obtained for sectional normal and tangential force coefficients were compared to available experimental data andmore » to the in-house performance code XTurb-PSU. It was observed that the ALM results agree well with measured data and results obtained from XTurb-PSU except in the root and tip regions if a three-dimensional Gaussian of width, ε, constant along the blade span is used to project the actuator force onto the flow field. A new method is proposed where the Gaussian width, ε, varies along the blade span following an elliptic distribution. A general criterion is derived that applies to any planform shape. It is found that the new criterion for ε leads to improved prediction of blade tip loads for a variety of blade planforms and rotor conditions considered.« less
  • The actuator line model (ALM) is a commonly used method to represent lifting surfaces such as wind turbine blades within large-eddy simulations (LES). In the ALM, the lift and drag forces are replaced by an imposed body force that is typically smoothed over several grid points using a Gaussian kernel with some prescribed smoothing width e. To date, the choice of e has most often been based on numerical considerations related to the grid spacing used in LES. However, especially for finely resolved LES with grid spacings on the order of or smaller than the chord length of the blade,more » the best choice of e is not known. In this work, a theoretical approach is followed to determine the most suitable value of e, based on an analytical solution to the linearized inviscid flow response to a Gaussian force. We find that the optimal smoothing width eopt is on the order of 14%-25% of the chord length of the blade, and the center of force is located at about 13%-26% downstream of the leading edge of the blade for the cases considered. These optimal values do not depend on angle of attack and depend only weakly on the type of lifting surface. It is then shown that an even more realistic velocity field can be induced by a 2-D elliptical Gaussian lift-force kernel. Some results are also provided regarding drag force representation.« less
  • When using an actuator-line representation of a wind turbine for computational fluid dynamics, it is common practice to volumetrically project the line force onto the flow field to create a body force in the fluid momentum equation. The objective of this study is to investigate how different volumetric projection techniques of the body force created by an actuator-line wind turbine rotor model affect the generated wake characteristics and blade loads in a turbine-turbine interaction problem. Two techniques for the body-force projection width are used , and they are based on either i) the grid spacing, or ii) the combination ofmore » grid spacing and an equivalent elliptic blade planform. An array of two NREL 5-MW turbines separated by seven rotor diameters is simulated within a large-eddy simulation solver subject to offshore neutral and moderately-convective atmospheric boundary-layer inflow. Power, thrust,and bending moment histories of both turbines, the statistics of angle of attack and blade loads over 2000 sec, variations in the mean and fluctuating velocity components, and turbulent kinetic energy and selected Reynolds stresses along vertical and spanwise sampling locations in the wake are analyzed. Comparisons for the different techniques of determining the body-force projection width of the actuator-line method are made and their effect on different physical quantities are assessed.« less