Torque Limit of Horizontal Axis Wind Turbine

Abstract

The torque coefficient of any wind turbine must have highest limit. In this paper, an analytical expression of torque coefficient associated with tip speed ratio and airfoil lift drag ratio of wind turbine with ideal chord has been deduced by integrating along the blade wingspan using the blade element momentum theory, which can be used for pre-estimating torque coefficient of actual wind turbine in design. Further, considering ideal fluid environment ( the drag coefficient is close to 0 ), an expression of the highest performance of torque only associated with tip speed ratio has been deduced too, which is the highest boundary of torque coefficient of any actual wind turbine with same tip speed ratio. The results show that for the wind turbine in steady operation state when the tip speed ratio is about 0.635, there is a theoretical limit of the torque coefficient, 0.401; if the tip speed ratio is greater than 6, the torque coefficient is unlikely to exceed 0.1. Keywords-wind energy utilization; horizontal axis wind turbine; torque coefficient; torque limit; highest performance; lift drag ratio; tip speed ratio