An experimental and numerical study of the performance of a model turbine

The performance of a 0.9 m diameter model wind turbine using the National Renewable Energy Laboratory S826 airfoil profile has been investigated both experimentally and numerically. The geometry was laid out using blade element momentum (BEM) theory, and a detailed description of the geometry is given here. The design was tested experimentally and gave a peak power coefficient of C P  = 0.448 at the design tip speed ratio of λ  = 6. After the model tests had been undertaken, numerical calculations were performed by means of fully three‐dimensional computational fluid dynamics (CFD) simulations using a k − ω turbulence model. It was found that the BEM correctly predicts the shape of the power and thrust coefficient curves, with the efficiency coefficient virtually identical to the measurements at the design conditions. At higher tip speed ratios, the performance is over‐predicted. The estimated thrust was, however, consistently too low by a shift of the order of ΔC T  ∼ 0.1 in the normal operating tip speed range. The high‐resolution CFD predictions (using about 3.5 ×10 6 grid points) reproduced the model thrust coefficient almost perfectly, and the predicted power coefficients were also very close to the measurements, although the agreement with the measurements at high tip speed ratios were only marginally better than those from the BEM method. At the design tip speed ratio, the CFD over‐predicted the power coefficient by merely 2%. The good agreement between the measured and computed performance at model scale assures that accurate predictions of turbine performance at full‐scale conditions are also possible with high‐resolution CFD. Copyright © 2011 John Wiley & Sons, Ltd.