|dc.description.abstract||In order to decrease the average costs of energy, wind turbines are arranged in wind farms where aerodynamic interactions between the turbines occur. When planning and optimizing the performance of a wind farm, these interactions have to be taken into account. Control algorithms for wind farms, which adjust the pitch angle and the tip speed ratio of each turbine in a wind farm individually show potential for optimizing the overall power output of a wind farm.
In this study the effect of the pitch angle of a turbine on the performance characteristics of the turbine itself and furthermore, on a turbine operating downstream of the pitched turbine, is investigated. Therefore, an experimental study is carried out in the wind tunnel at the Norwegian University of Science and Technology (NTNU) in Trondheim. The power and thrust coefficients of a turbine with pitched blades are measured for eight different pitch angles. The maximum power production is measured for a pitch angle of β(T1) = +5° and a tip speed ratio of λ(T1) = 6. Furthermore, the wake behind the pitched turbine is measured for three different pitch angles and the resulting difference in the velocity deficit caused by the pitch angle is analysed. In order to evaluate the effect of the pitch angle on a turbine operating downstream of the pitched turbine, a second model turbine is set in the wind tunnel at two distances. For the distance x/D(T2) = 5.18 an improvement of 3.7% of the overall efficiency is reached when T1 is pitched to β(T1) = −5°.
Furthermore, two models for estimating the influence of the pitch angle variation on the power output of the downstream turbine are developed. First the power density in the wake behind the pitched turbine is calculated. The power density of wakes at different pitch angles is then compared. This model allows qualitative assumptions of the influence of the pitch angle on the power output of the second turbine. In order to take the different contribution of the blade elements to the power production into account a Blade-Element-Momentum (BEM) code for non-uniform inflow fields is developed. This code takes the measured wake data as inflow field for the downstream turbine into account. The BEM simulations underestimate the performance characteristics of the downstream turbine but show good agreement with the shape of the power and thrust coefficients.
Keywords: Wind Energy, Pitch Control, Blade-Element-Momentum, Wind Farm Optimization||en