Demonstrating Predictive Capability of Validated Wind Turbine Blade Models

Abstract

Verification and Validation (V&V) activities provide a means by which credibility can be established for simulation models developed to predict the behavior of wind turbines. This paper discusses the use of validation activities in the development of finite element (FE) models for wind turbine blades. The nine-meter CX-100 wind turbine blade, developed at Sandia National Laboratories (SNL), is utilized in this study. The FE model is developed using design specifications for the geometry of the blade, and the rule of mixtures is applied to smear the cross section so that it can be represented using isotropic material properties. Experimental modal data from laboratory tests of the CX-100 blade at the National Renewable Energy Laboratory (NREL), is collected for a fixed-free boundary condition, in which the blade is bolted to a 20 t steel frame. The experimental modal data is collected in two configurations: (1) in the original fixed-free condition and, (2) with two masses attached to the blade at the 1.6 and 6.75 m stations. To mimic the second experimental configuration, the FE model is modified by incorporating point masses attached to the blade with springs. Calibration of the fixed-free and mass-added FE models is limited to use of the natural frequencies only. By exploring these different configurations of the wind turbine blade, credibility can be established regarding the ability of the FE model to predict the response to different loading conditions. Through the use of test-analysis correlation, the experimental data can be compared to model output and an assessment is given of the predictive capability of the model. (Publication approved for unlimited, public release on September 26, 2011, LA-UR-11-5490, Unclassified.)