Several types of single-plane and multiplane Wells turbines are investigated and compared. The turbines’ aerodynamic losses and overall performances are presented and two successful methods of swirl energy recovery are studied in detail. Guide vanes were fitted to a monoplane turbine whereas the rotors of a biplane turbine were contra-rotated. A double-shaft biplane turbine was also tested. The contra-rotating turbine had an operational range which was similar to that of the monoplane turbine with guide vanes, achieved a similar peak efficiency, but performed better in the post-stall region and also was found to be able to accommodate a much higher pressure-flow ratio.