Abstract
Empirical data serve as the foundation to computational modeling in the initial stages of the wind turbine design process. In case of aerodynamic simulations, the empirical input is comprised of lift and drag data obtained in quasi two-dimensional wind tunnel tests. In the simulations, the global flow over an entire blade is finally approximated as a spatial summation of the obtained 2-D data, which stands in strong contrast to the true operation of a wind turbine and consequently leads to a higher level of uncertainty. Especially, the near-root region of the blade experiences highly three-dimensional flow conditions, particularly in regions of the blade where the flow separates from the airfoil. This study aims to accentuate the difference between airfoil data obtained in quasi two-dimensional wind tunnel tests compared to airfoil data from a wing with an imposed three-dimensional spanwise pressure gradient. For this, a geometrically altered wing section with a spanwise twist is tested in a wind tunnel and compared to CFD computations.
Highlights
Before a wind turbine prototype is built and the final model goes into production, an iterative design process determines the basic layout of the turbine
To investigate the effects of a spanwise pressure gradient on a three-dimensional wing, a blade section based on the DU91-W2-250 profile with constant chord length but a spanwise twist of θ = 10◦ was 3-D printed including pressure taps at midspan
The blade section was mounted in a wind tunnel and the chordwise pressure distribution was measured for Reynolds numbers between 0.2 · 106 and 0.5 · 106 at angles of attack between −10◦ and 25◦, where the angle of attack is defined at the midspan
Summary
Before a wind turbine prototype is built and the final model goes into production, an iterative design process determines the basic layout of the turbine. The available computational power nowadays allows to carry out sophisticated and detailed flow (CFD) and structural analyses (FEM), which replicate real world aerodynamics and the corresponding loads in accurate detail. These simulation tools come among others with the drawback of higher computational cost, which limits their use to detailed improvements in the final stages of the design process before a first prototype of the wind turbine is built. In the case of aerodynamic simulations, the semi-empirical data are commonly comprised of two-dimensional lift and drag data of airfoil sections. The global flow over the blade is approximated as the sum of multiple two-dimensional flows at the particular
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