Aspects of the Dynamic Response of a Small Wind Turbine Blade in Highly Turbulent Flow: Part 2 Predicted Blade Response

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Abstract
The work described in this paper compares the measured blade root flapwise bending moment on a 400W 3-bladed wind turbine to analytical predictions and calculations from the “simple load model” of the International Electrotechnical Commission safety standard for small wind turbines. The predictions use the method of Eggleston and Stoddard (1987) and were found to over predict the measured azimuthal averaged flapwise root bending moment. During an extreme yaw event, the instantaneous blade root flapwise bending moment was found to be dominated by the gyroscopic moment from the blades. The calculated fatigue loads from the safety standard were some 25% lower than the measured values, with the calculated yaw moment under-predicting the measured flapwise bending moment for a range of turbine yaw rates with the error increasing with increasing blade rotational speed. A Combination of the calculated root bending moment from yaw and yaw error was found to over-estimate the root flapwise bending moment especially at high rotational speeds.