Optimization of Dual Rotor Wind Turbine with Double Rotational Armature Using Configurable BEM Method, Validated by Wind Tunnel Measurement

Abstract. Small wind turbines (SWTs) face significant challenges in achieving commercial viability due to lower efficiency and higher energy costs compared to utility-scale systems and competing renewable technologies. Counter-rotating dual rotor wind turbines (CR-DRWTs) with dual rotational armature configurations offer a potential pathway for efficiency improvements through doubled direct drive power, minimal mechanical complexity, and reduced noise characteristics suitable for urban applications. This study investigated the aerodynamic performance of a 1.6 m diameter CR-DRWT through wind tunnel testing at the Centre Scientifique et Technique du Bâtiment (CSTB) in Nantes, France, at wind speeds ranging from 4 to 15 m/s. Enhanced instrumentation including RPM and pitch angle sensors provided detailed operational measurements. The turbine achieved maximum power output of 1014 W and a peak power coefficient (CP) of 0.33, and demonstrates reliable self-starting capability at 3.5 m/s. A Blade Element Momentum (BEM) model was adapted for dual rotational armature systems and validated against experimental data, showing good overall agreement. Differential evolution optimization algorithms identified optimal operational parameters with upstream rotor pitch angles of 9.8° and downstream angles of 0.6°, both operating at tip-speed ratios near 6. The optimized configuration predicted a theoretical maximum CP of 0.51, indicating substantial performance improvement potential. The study demonstrates that dual rotational armature CR-DRWT eliminates gearbox requirements while maintaining competitive performance, offering a mechanically simpler and potentially more cost-effective solution for small-scale wind energy applications, particularly in urban environments where compactness and low noise are critical design constraints.