Design, simulation, and experimental evaluation of a novel three-stage coaxial counter-rotating wind turbine

This paper presents the design, aerodynamic simulation, and experimental validation of a novel three-stage horizontal-axis wind turbine (HAWT) with coaxial and independently rotating rotors. Building on the dual-rotor architecture widely studied in recent years, the proposed configuration introduces a third rotor with a larger radius (120–125% compared to the first two rotors) to harness the remaining wind energy passing through upstream stages. The rotors rotate in opposite directions to increase the relative velocity of magnetic field interaction, thereby improving electrical generation efficiency. The aerodynamic behavior of the turbine was analyzed using XFlow software with the Lattice-Boltzmann Method (LBM), enabling large eddy simulations (LES) on an octree mesh to capture flow interactions and wake effects. The optimized blade geometry and spacing were determined through simulation, focusing on maximizing energy extraction at low to moderate wind speeds (3–9 m/s). A 3D-printed experimental prototype was developed using GOE222 airfoil profiles and tested in a controlled wind tunnel environment. The test setup allowed selective activation of one, two, or all three rotor stages to isolate and compare their respective power outputs. Results demonstrated that the three-stage turbine consistently outperformed both single-stage and dual-stage configurations. Notably, power output increased by 30%–94% compared to the two-stage design, and up to 703% compared to the single-stage model at lower wind speeds. This study demonstrates the significant potential of multi-stage, counter-rotating turbines in small and medium-scale applications, offering a viable path toward higher efficiency and improved energy harvesting from wind resources.