Parametric Study of a Diffuser for HAWT Power Augmentation

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Addis Ababa University


The paper is a compilation of a work involving the study of the parametric relationship of geometric parameters of a diffuser for power augmentation for horizontal axis wind turbines (HAWTs). Various works of researchers are studied and hypotheses and possible optimization techniques are put together to depict the picture of power augmentation. The bottom line shows that the power output and performance of a wind turbine can be improved through the use of diffusers. The effect of the use of these devices is to increase the mass flow rate at the rotor plane. This significantly augments the power developed by the wind turbine due to the cubic relationship of wind speed and power. This increase in speed, represented by the acceleration factor or velocity ratio, �� ��∞ , is dependent on the geometry of the concentrator device, specifically the diffuser. The basic diffuser geometry parameters were identified and their relationships were formulated based on CFD results. A commercial software, ANSYS-Fluent, is used for simulation where the results are analyzed with MS-Excel and Matlab. The results show good agreement with previous works. Due to the presence of a diffuser in the flow field, the velocity ratio along the central axis of the diffuser shows an increase as the flow approaches the diffuser inlet. The velocity peaks at a location immediately after the diffuser inlet. The velocity, then, levels off and further decreases as the flow continues to the diffuser outlet and exits it. This suggests a possible location of a wind turbine at the vicinity of the inlet. The length of the diffuser and the flange height were the major parameters considered in this study. Their relationship with velocity ratio was analyzed and the results show that both have a direct relationship with the velocity ratio. The no-flange configuration showed a 32.5% increase in the on-axis wind speed in reference to the bare wind turbine configuration. The flanged configurations showed a 45% and 51% increase on the on-axis wind speed with = 0.1 ������ 0.2, respectively. The maximum power augmentation ranges from two-to-three times the power produced by a comparable bare wind turbine. The mathematical relations obtained for the major parameters and the velocity ratio can be used in the performance prediction and optimization of a diffuser. Finally, possible directions of further research and work are recommended