Performance prediction of a small-scale diffuser-augmented wind turbine with and without an inlet nozzle: A 2D and 3D analysis

This paper presents a novel comparative study of six different diffuser configurations used with a small-scale wind turbine, analyzed through both 2D and 3D approaches. These diffuser configurations are divided into two categories: without inlet nozzles and with inlet nozzles. The 2D approach is adopted to assess the feasibility of using its results for comparative analysis between different configurations. Subsequently, the 2D approach could be employed in preliminary design stages before performing the 3D simulations, thereby the computational costs could be reduced. In the 3D approach, a small-scale wind turbine is tested with the six different diffuser configurations across various tip speed ratios. In the 2D approach, the turbine is modelled as a uniform actuator disk or a load with different load coefficient values. Both 2D and 3D developed models were validated against experimental data from the literature. The key parameters investigated include the air mass flow rate through the diffuser, the drag force acting on the diffuser, and the extracted power by the turbine or the load. The extracted power in the 2D approach is calculated using two equations: one neglects the change in the dynamic pressure across the load, while the other accounts for it. The primary finding of this study is that neglecting the change in the dynamic pressure in the 2D approach can lead to misleading results regarding the performance of diffuseraugmented small-scale wind turbines. Additionally, the 3D analysis indicates that attaching an inlet nozzle to the diffuser does not significantly enhance the turbine's output power, corroborating experimental findings from existing literature. Similar observations are noticed from the 2D approach when using the power equation that considers the total pressure change across the load instead of the static pressure change. The turbine's maximum power coefficient of approximately 40 % was obtained for the diffuser with a 10-mm-flat flange and it was less by about 1.9 % when attaching the inlet nozzle.