Dr Sam Evans

© 2019, Springer Nature Switzerland AG. Small wind turbines are usually sited in more complex environments than the open terrain sites, such as urban built environment. However, the international small wind turbine design standard IEC61400.2 is based on the measurements of flat and open terrain. Failures of SWTs operational in urban area predicts the inadequacy of turbine design for the turbulent wind resource at the sites. This study investigates the wind speed in the vertical direction at a complex terrain site, where a small 5¿kW Aerogenesis horizontal-axis wind turbine is in operation and subject to an ongoing research. Wind measurements were acquired at 20¿Hz using 3 three-axis ultrasonic anemometers equispaced around the tower of the wind turbine. The results show significantly high wind speeds (8¿12¿ms -1 ) in the vertical direction. High fluctuation of vertical wind speed was observed with standard deviation >2¿ms -1 . In addition, the turbulence in vertical direction was found to be 20% higher than the IEC 61400.2 level. The result of this study is important for the small wind turbine developers as they seek best practice for determining turbine operating loads.

© 2019, Springer Nature Switzerland AG. This paper presents measurements and predictions of the yaw performance of a small 5¿kW horizontal-axis wind turbine operating in unsteady flow fitted with a delta wing tail fin of two different sizes. Measurements show the smaller of the two tail fins causes the turbine to operate at a higher mean yaw error than the larger tail fin and to respond at a higher yaw rate than the larger tail fin, over most of the operating wind speed range for the turbine. Unsteady slender body theory was used to predict the dynamic performance of the tail fin. The dominant steady lift term in this theory assumes lift is linear with flow angle of attack, a, a valid assumption for a < 40°. Experimentally determined coefficient of lift and drag data and an analytical non-linear relationship for the coefficient of lift and drag as a function of a for the delta wing were also used in steady lift term. The relative motion of the yawing tail fin and the effects of the reduced wake velocity on the tail fin performance were also considered. Unsteady slender body theory incorporating experimentally determined data, with the inclusion of relative motion and reduced wake velocity gave the highest correlation with experimental results.

© 2018 It is well known that wind turbine blades are fatigue critical, with much literature and methodologies available for assessing fatigue loading of large wind turbine blades. Little research effort has been directed at assessing the fatigue life of small wind turbines which operate at higher rotational speeds and are subject to highly unsteady aerodynamic loading. In this paper the simplified load model proposed in IEC 61400.2 is used to determine the fatigue life of a small 5 kW wind turbine blade. This estimated life is compared to that determined from both measured operational data and aeroelastic simulations. Fatigue life was estimated by the standard at 0.09 years, compared to 9.18 years from field measurements and 3.26 years found via aeroelastic simulations. All methods fell below the 20 year design life, with the standard over-conservative by a factor of 102 and 36 for measurements and simulations respectively. To the best of the authors¿ knowledge these three fatigue methods specified in the standard have not been quantitatively compared and assessed for small wind turbines. Results are of importance to small wind turbine developers as they seek best practice for determining blade fatigue life. Shortcomings of the IEC methodology are detailed and discussed.