Computational modeling of the aerodynamics of windmill blades at high solidity

摘要

Water pumping is one or the oldest uses or wind energy with the multi-bladed, high-solidity windmill still in widespread use. In contrast to the low-solidity, high-speed blades of modern wind turbines which use airfoil profiles, windmills typically employ thin, circular-arc blades at high solidity and low speed. While there is considerable data on the aerodynamic behavior of circular arc airfoils (of zero solidity) there is very little data on cascades of circular arc blades. This paper investigates computationally the effects of solidity on the lift and drag of thin, circular arc blades in preparation for a detailed blade element analysis of windmill performance. Typical Reynolds numbers, Re, for windmills are around 10~5, so modeling of laminar separation and transition was expected to be as important as modeling the subsequent turbulent flow. The SST-transition model was, therefore, used. The "constants" in the transition equations were adjusted to match surface pressure measurements on circular arc airfoils at Re = 62,000, and then compared to separate measurements of the lift and drag at Re = 10~5. Excellent agreement was found in the former but the agreement for the latter was poorer. Computational modeling of solidity showed significant variation in the lift and drag which should be included in a blade element calculation.