Design and Development of a Wind Turbine with Flanged Diffuser Operating in Low Wind Speed Regime

In this paper, the performance characteristics of a fabricated horizontal axis wind turbine with and without flanged diffusers were studied using wind tunnel experiment. Measurements of global parameters (power, torque, rotational speed efficiency, etc.) were carried out at wind speed regime between 3-7 m/s. Flanged diffusers of five different inlet-outlet diameter ratios were employed. The results showed minimum mean increments in tip-speed ratios (TSR) of about 45 % with the smallest diffuser and a maximum of 80 % with the largest diffuser. Increments in the torque even at modest wind speed of 4 m/s were as much as 65, 70 and 76 % for the largest three diffusers and about 33 % for the smaller diffuser. The power output (with and without diffuser) gradually increased from 3-7 m/s wind speed, while the power coefficient (Cp) increased from 3-5.5 m/s, and thereafter began to fluctuate as the wind speed approached 7 m/s. Comparatively, maximum Cp of the turbine without diffuser was 0.22 for λ=0.534 at a wind speed of 7 m/s, while the maximum average value of Cp for turbine with flanged diffuser 3 was 0.34 for λ=0.706 at the same wind speed. As a result of the flanged diffuser attachment, the maximum Cp increased by 36 %. The results showed mean incremental values of 52 and 57 % with the greater value obtained from the second largest diffuser (Di/Do = 0.70) and the least value from the largest diffuser (Di/Do = 0.80), while the first three diffusers achieved near identical increments of 55 %. This consequently implies that increments in the extracted power (i.e., Cp) above 5 m/s wind speed declined with indications of separation and turbulence in the flows beyond the rotor.