Performance investigation of Wells turbine for wave energy conversion with stall cylinders

The wave energy conversion of oscillation water column (OWC) systems is limited by the narrow range of efficient operation of Wells turbines. Effective control methods are critical to improving performance. In this study, spanwise stall cylinders were mounted near the blade leading edge to delay the stall using dynamic mode decomposition (DMD) analysis. The performance of the Computational Fluid Dynamics simulation with steady inflow conditions is in good agreement with the experimental data. The results indicate that the aerodynamics and turbine performance is significantly influenced by cylinder wakes, which are associated with the location and radius of the stall cylinders. The relatively optimal location of the stall cylinders is determined at a 10% chord of the blade with a radius of 1% of the chord, producing 19.15% and 26.57% increases in the operation range and maximum torque coefficient, respectively. The cylinders act by intensifying the turbulence in the boundary layer and weakening the tip leakage vortex, causing the cylinder wake vortices to interact with vortices near the boundary layer to guide the flow near the suction side. A larger cylinder radius produces stronger wake vortices, but the efficiency decreases due to increased dissipation losses.