Performance analysis of diffuser-augmented wind turbines with swept rotor

Abstract

This work presents a novel performance analysis model of diffuser-augmented wind turbines (DAWT) with swept blades, considering the influence of diffuser efficiency and thrust. Blade element momentum theory (BEMT) is extended to incorporate the effect of blade sweep at each radial position along the rotor. An algorithm is developed and implemented to evaluate the performance of wind turbines with diffuser and sweep effect based on the BEMT model. The impact of the diffuser is assessed through the augmentation factor, defined as the ratio between the turbine efficiency and the Betz-Joukowsky limit. The comparison between the experiment and the algorithm considers the same rotor and diffuser geometry used by Hoopen [1]. The straight blade is optimized to include the sweep effect. The model is validated using the experimental results provided by Hoopen [1], which include a power output of 531.0  W, a torque of 7.10 Nm, and a thrust coefficient of 0.80. The simulations using the proposed model with straight blades result in power of 532.6 W, torque of 7.10 Nm, and thrust coefficient of 0.77, compared to power of 531.0 W, torque of 7.10 Nm, and thrust coefficient of 0.80 from the experimental data. The optimized rotor with a forward sweep effect at 40° presented the highest power at 541.60 W, torque of 7.22 Nm, and a thrust coefficient of 0.63. Furthermore, the optimized rotor with backward sweep effect of 30° resulted in the highest power at 542.3 W, torque of 7.23 Nm, and a thrust coefficient of 0.69. The augmentation factor and power coefficient achieved a good gain in performance with the rotor optimized at 30° and 40°. Therefore, applying the sweep effect in a DAWT can result in a considerable increase in energy production.