Integrated design of high-solidity micro-scale counter-rotating wind turbines at extreme close spacing

Micro-scale counter-rotating wind turbines (CRWTs) offer enhanced potential for wake energy recovery. This study proposes an integrated cascade-coupling design framework for high-solidity CRWTs, in which rear rotor geometry and rotor coupling are co-designed based on stereoscopic particle image velocimetry measurements of the front rotor wake. Experiments are conducted at a tip-speed ratio of λ = 1.0, solidity σ = 1.25, and spacing ratios of d = 0.6R T , 1.0R T , and 3.0R T , and the tip-radius is R T = 70 mm. At the physical limit spacing of d = 0.6R T , the integrated design increases the system power coefficient by 24.1% while limiting front rotor power reduction to 17.2%, compared to a 10.3% system gain and 34.5% front rotor suppression for the baseline mirrored configuration. Wake measurements confirm near-complete absorption of rotational kinetic energy from the frontrotor wake without exacerbating upstream interference. These results demonstrate that cascade-based energy extraction and coupling-based interference mitigation can operate synergistically, enabling compact, high-performance micro-scale CRWTs suitable for spaceconstrained and urban energy applications.