Some effects of finite solidity on the aerodynamics of horizontal-axis wind turbines

Abstract

This paper describes an exploratory, computational study of the effects of local solidity on the aerodynamics of a horizontal-axis wind turbine. The parameters governing the path of the trailing vorticity in the crude model employed were chosen to match the circulation measured behind a two-bladed model turbine by previous workers. Traditional blade element theory, which assumes two-dimensional aerofoil characteristics, significantly underestimated the measured circulation at high angles of incidence. The calculations suggest that the major departure from two-dimensional behaviour is a reduction in the surface vorticity near the leading edge due to the trailing vorticity of a blade. This reduction, which is a consequence of finite local solidity, appears sufficient to prevent boundary layer separation at angles at which this would occur for two-dimensional flow. The magnitude of the reduction decreases as the angle of incidence is reduced. The results suggest that the optimization of wind turbine design will require fully three-dimensional modelling.