Abstract
To analyse the sensitivity of blade geometry and airfoil characteristics on the prediction of performance characteristics of wind farms, large-eddy simulations using an actuator disc (ACD) method are performed for three different blade/airfoil configurations. The aim of the study is to determine how the mean characteristics of wake flow, mean power production and thrust depend on the choice of airfoil data and blade geometry. In order to simulate realistic conditions, pre-generated turbulence and wind shear are imposed in the computational domain. Using three different turbulence intensities and varying the spacing between the turbines, the flow around 4-8 aligned turbines is simulated. The analysis is based on normalized mean streamwise velocity, turbulence intensity, relative mean power production and thrust. From the computations it can be concluded that the actual airfoil characteristics and blade geometry only are of importance at very low inflow turbulence. At realistic turbulence conditions for an atmospheric boundary layer the specific blade characteristics play an minor role on power performance and the resulting wake characteristics. The results therefore give a hint that the choice of airfoil data in ACD simulations is not crucial if the intention of the simulations is to compute mean wake characteristics using a turbulent inflow.
Highlights
The actuator disc (ACD) method (Sørensen and Myken [1]) has been largely exploited in the last two decades and has proven to be a reliable tool for wind farm power predictions in combination with large-eddy simulations.Later contributions in the field using LES are due to, among others, Ivanell et al [3], PorteAgel et al [4], Troldborg et al [5][6], Churchfield et al [7], Keck et al [8] and Troldborg et al [9]
Due to the shape of the farm layouts, the LG data is based on a single row of turbines (Row D in Nilsson et al [2]) while the Horns Rev (HR) data is based on averaging of all rows in the farm
It is emphasized that the actual comparison in this study is between different rotor configurations and that the measurement data only is used to show that the production levels in the simulations are at an adequate level
Summary
The actuator disc (ACD) method (Sørensen and Myken [1]) has been largely exploited in the last two decades and has proven to be a reliable tool for wind farm power predictions in combination with large-eddy simulations (see e.g. Nilsson et al [2]).Later contributions in the field using LES are due to, among others, Ivanell et al [3], PorteAgel et al [4], Troldborg et al [5][6], Churchfield et al [7], Keck et al [8] and Troldborg et al [9]. Porte-Agel et al [4] studied the velocity and the turbulent statistics after a single turbine using an ACD method with constant loading (this method is referred to as ACD-NR), an ACD method which uses airfoil data and considers turbine-induced flow rotation (ACD) and an actuator line (ACL) method. Troldborg et al [5][6] performed LES computations using an ACL method on a single turbine in uniform inflow conditions and on two turbines where the inlet flow was varied to mimic laminar, offshore and onshore conditions. Troldborg et al [9] performed further verifications of the prescribed wind shear and the pre-generated synthetic turbulence described in Keck et al [8] using a simple linear shear approach. For an extensive list of different wake models, it is referred to Crespo et al [10] and Vermeer et al [11]
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