Design and Optimization of Dual Darrieus Wind Turbines Using Computational Fluid Dynamics and Orthogonal Test Method

Dual Darrieus wind turbines (DDWTs) comprise two combined layers of Darrieus rotors. Previous investigations, however, only revealed the enhancement of wind power capture ability concerning one single structural parameter. To comprehensively study the interaction impact between the parameters and discover the optimal configuration, this study applies a combination method of Computational Fluid Dynamics (CFD) and Orthogonal Test (OT), focusing on the effect of chord ratio, radius difference, and offset angle. In addition, two types of conventional Darrieus rotors as the benchmark cases are included in the numerical analyses at Tip Speed Ratio (TSRs) between 3.5 and 5.0. Among the 27 configurations of DDWTs generated by the Orthogonal table L<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">27</inf>(3<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup>), optimal combination of parameters with the chord ratio of 3, the radius difference of 0.25m and the offset angle of 90 degrees. The numerical results reveal that the optimal DDWT features a better power coefficient, increased by 8.488% compared to the conventional Darrieus rotor in terms of the identical blade number and solidity. Moreover, the performances of DDWTs are significantly affected by the chord ratio and its interaction with the radius difference. DDWTs present a promising solution for future multi-watt wind energy applications.