Low Wind Speed Characteristics of an Optimized Diffuser Augmented Wind Turbine

Abstract Towards a final aim of enhancing the feasibility of low-speed sites for wind energy generation, the current study introduces the diffuser augmentation as a method of enhancing the performance of wind turbines designed for poor wind conditions. The study uses a methodology that combines the MOGAII Genetic Algorithm (GA) and Computational Fluid Dynamics (CFD) to generate a novel optimized diffuser profile out of nearly 200 geometric shapes. A case for each of the bare turbine and the diffuser-augmented turbine were modeled using 3-dimensional Reynolds Averaged Navier Stokes equations (RANS) using k-ω SST model and FLUENT solver. The performance comparison indicated an overall average rise of 28.83% in power coefficient in favor of the diffuser-augmented case. The most significant performance rise of 47.19% was found at the low-speed region corresponding to Tip Speed Ratios between 8 and 12. Through investigating the starting torque at extremely low speeds above 1 m/s, it was evaluated that the starting torque increases significantly with an average rise of 60.64% in favor of the diffuser-augmented case, the enhanced starting torque widened the operational range of the wind turbine in the low wind speed region, and reduced the lowest required speed to induce a positive moment coefficient. This significant rise in performance particularly for low wind speeds which are dominantly more frequent in the annual wind conditions, combined with the enhanced starting capabilities, resulted in an annual generated energy increase of 23.18% compared to the bare turbine.