Comparison of Performance and Unsteady Loads of Multimegawatt Downwind and Upwind Turbines

Abstract

The benefits and drawbacks of a multimegawatt downwind compared to upwind wind turbine are assessed using unsteady, three-dimensional (3D) computational fluid dynamics. For the same operating conditions, the downwind turbine has a 3% higher output power and a similar mean flapwise root bending moment. However, in comparison to the upwind turbine, the downwind turbine has a 3% higher thrust and a factor 3 larger peak-to-peak unsteady loading. These features arise due to higher flow incidences on the blade, higher axial velocities ahead of the rotor, and higher loading on the inboard span of the blade when the downwind turbine is compared to the upwind turbine. Overall, it is concluded that the downwind turbine configuration may be better suited for the design of multimegawatt offshore wind turbines.