Geometric and Control Optimization of an Array of Two Cross-Flow Turbines

Cross-flow turbines, also known as vertical-axis turbines, convert kinetic energy in wind or flowing water to mechanical power via blades that rotate about an axis perpendicular to the flow. Interactions between two cross-flow turbine rotors operated in a flume were experimentally optimized. Under “tip-speed ratio control”, the rotation rate of each turbine was individually optimized to take advantage of the mean flow structure. Under “coordinated control”, periodic rotor interactions were exploited by operating each rotor at identical rotation rates. The rotation rate and blade position difference between the rotors is optimized. Control parameters were optimized to maximize array power output using a modified Nelder-Mead algorithm for Sixty-four array geometries. Both control schemes produced a maximum power output of 1.3 times the power generated by two isolated turbines. Tip-speed ratio control outperformed coordinated control where the downstream turbine was located directly in the wake of the upstream turbine, while coordinated control was more successful for other array geometries. Co- and counter-rotating configurations produced similar maximum power output, though beneficial array interactions occurred over a broader range of array geometries with counter-rotation.