Abstract
The yawing of horizontal-axis wind turbines (HAWT) is a major topic in the comprehension of the dynamical behavior of these kinds of devices. It is important for the study of mechanical loads to which wind turbines are subjected and it is important for the optimization of wind farms because the yaw active control can steer the wakes between nearby wind turbines. On these grounds, this work is devoted to the numerical and experimental analysis of the yawing behavior of a HAWT. The experimental tests have been performed at the wind tunnel of the University of Perugia on a three-bladed small HAWT prototype, having two meters of rotor diameter. Two numerical set ups have been selected: a proprietary code based on the Blade Element Momentum theory (BEM) and the aeroelastic simulation software FAST, developed at the National Renewable Energy Laboratory (NREL) in Golden, CO, USA. The behavior of the test wind turbine up to ± 45 ∘ of yaw offset is studied. The performances (power coefficient C P ) and the mechanical behavior (thrust coefficient C T ) are studied and the predictions of the numerical models are compared against the wind tunnel measurements. The results for C T inspire a subsequent study: its behavior as a function of the azimuth angle is studied and the periodic component equal to the blade passing frequency 3P is observed. The fluctuation intensity decreases with the yaw angle because the distance between tower and blade increases. Consequently, the tower interference is studied through the comparison of measurements and simulations as regards the fore-aft vibration spectrum and the force on top of the tower.
Highlights
The yawing behavior of wind turbines has attracted a considerable amount of interest in the scientific literature about wind energy
Excessive yaw rates and yaw loads can severely impact on the reliability of a wind turbine (Hansen [1], Ekelund [2], Micallef [3]): for example, in Bakshi [4], the effects of yaw error on the reliability of blades is estimated by performing load and stress analysis for various yaw errors
This work has been devoted to a topic that has been attracting recently a certain amount of attention in wind energy literature, mainly because of the interest in wind farm cooperative control and wake steering, but is still overlooked by several points of view: the yawing behavior of horizontal-axis wind turbines
Summary
The yawing behavior of wind turbines has attracted a considerable amount of interest in the scientific literature about wind energy. Yaw error can impact impressively on the power output production: for example, in Wan [5], an equivalent wind speed model and a yaw error model are employed for simulating the impact of yaw misalignment on the power production of a multi-megawatt wind turbine It arises that, approaching rated power, an average misalignment of 10◦ can decrease the power production up to 10%: for this reason, interest is growing as regards yaw misalignment diagnosis through lidar (Mikkelsen [6], Fleming [7], Pedersen [8]) and-or nacelle anemometer data mining (Astolfi [9], Pei [10]). In Schottler [11], Trujillo [12], Schottler [13], Bromm [14], the wake deviation is studied in relation to yaw misalignment
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