Net Power Coefficient of Vertical and Horizontal Wind Turbines with Crossflow Runners

Abstract

The feasibility of using crossflow runners as single rotors in vertical-axis wind turbines (VAWT) or as blades in horizontal-axis wind turbines (HAWT) is numerically studied. A computational fluid dynamics model is validated from data obtained in a wind tunnel. Three crossflow runners with different number of blades are tested. Values of drag, lift and torque coefficients are numerically obtained at different turning velocities. Power coefficients Cp for crossflow VAWT and HAWT are calculated for different tip-speed ratios (TSR) and runner spin ratios (α). Since crossflow HAWT consume electrical energy for spinning the runners, the net power coefficient is estimated. Simulations indicate that a crossflow runner as a single rotor in VAWT should have a high solidity and work at low TSR. Crossflow runners working as blades in HAWT may achieve low drag to lift ratios but the Cp is penalized by the amount of energy required for spinning the runners. The optimum working condition of crossflow HAWT is located within a narrow band of low TSR and α reaching Cp values < 0.2 only