Modeling of unsteady aerodynamic effects on wind turbine performance
Recent interest in wind energy has increased the demand for accurate methods of wind turbine analysis. Among industry standards is the PROPPC computer program developed as a result of the work by R.E.Wilson and P.B.S.Lissaman especially for horizontal axis wind turbine performance predictions. In the current work, the non-uniform aerodynamic effects of yaw and tower shadow were investigated on three existing rotors, the Enertech 21-5, Carter 25 and the combined experiment machines taking into account the effect of dynamic stall. For this purpose, the original PROPPC code was enhanced by adding a graphical post-processor with contour and surface plots. The post-processor helps the user to visualize the variation of the different parameters along the blade and also at different angular positions of the blade. Non-uniform aerodynamic models for tower shadow and yaw were added to the code, taking into account the effect of dynamic stall. The models included are tower shadow, modeled by a cosine velocity deficit; yaw, modeled by considering the additional flows rn the rotor disc plane and dynamic stall modeled using the Gormont model with the Masse modification. The performance of Enertech 21-5 with these non-uniformities were then compared with the uniform flow case. Carter 25 was chosen to illustrate the performance variation with different blade geometries. The experimental data from the combined experiment wind turbine was used to compare with the predicted results obtained from the modified PROPPC code.Both the non-uniformities, tower shadow and yaw reduced the rotor power output for a given wind speed, although yaw didn't reduce the peak power output. Dynamic stall didn't have much effect on the rotor performance, the effect being a negligible increase in the rotor power at high wind speeds. The predicted results from the modified PROPPC code showed closer comparison with the experimental data when compared with the results obtained from the original PROPPC code. The PROPPC code in the present form with proper airfoil characteristics, can be used to calculate the rotor performance for virtually any blade geometry and tip speed ratio.