Abstract
Stall, a complex phenomenon related to flow separation, is difficult to be predicted accurately. The motivation of the present study is to propose an approach to improve the simulation accuracy of Reynolds Averaged Navier–Stokes equations (RANS) for wind turbines in stall. The approach is implemented in three steps in simulations of the S809 airfoil and the NREL (National Renewable Energy Laboratory) Phase VI rotor. The similarity between airfoil and rotor simulations is firstly investigated. It is found that the primary reason for the inaccuracy of rotor simulation is not the rotational effect or the 3-D effect, but the turbulence-related problem that already exists in airfoil simulation. Secondly, a coefficient of the SST turbulence model is calibrated in airfoil simulation, ensuring the onset and development of the light stall are predicted accurately. The lift of the airfoil in the light stall, which was overestimated about 30%, is reduced to a level consistent with experimental data. Thirdly, the calibrated coefficient is applied to rotor simulation. That makes the flow patterns on the blade properly simulated and the pressure distribution of the blade, as well as the torque of the rotor, are predicted more accurately. The relative error of the predicted maximum torque is reduced from 34.4% to 3.2%. Furthermore, the procedure of calibration is applied to the MEXICO (Model Experiments in Controlled Conditions) rotor, and the predicted pressure distributions over blade sections are better than the CFD (Computational Fluid Dynamics) results from the Mexnext project. In essence, the present study provides an approach for calibrating rotor simulation using airfoil experimental data, which enhances the potential of RANS in accurate simulation of the wind turbine aerodynamic performance.
Highlights
Aerodynamics is one of the most important topics in wind turbine technology
An approach of turbulence coefficient calibration has been proposed for accurate simulation of wind turbine stall
The similarity of error between the rotor and airfoil simulations is investigated on the S809 airfoil and the NREL Phase VI rotor
Summary
Aerodynamics is one of the most important topics in wind turbine technology. Accurate calculation of the aerodynamic loads is essential for the power prediction and the structural design. Researchers later attempted to improve the simulation by using various turbulence models such as k-ω used by Yang [13], S-A, SST and SA-DES used by Benjanirat [14], and SST and RNG k-ε used by Guerri [15] Their results repeatedly showed the same inaccuracy: predicting a late onset of stall and overestimating the maximum lift coefficient. Wolfe [16] specified a transition point, while Bertagnolio [17] and Langtry [18] employed the Michel model and the γ-Reθ model [19], respectively Their results showed that stall prediction depends on the simulation of transition, but it is still not accurate enough. The present study is devoted to achieving accurate stall prediction in wind turbine RANS simulations.
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