A design of experiment approach as applied to the analysis of diffuser-augmented wind turbines

Since the 1930s ducted-wind-turbines have received considerable attention due to the possibility of obtaining a significant increase in the extracted power compared to an open turbine with the same rotor swept area. The incomplete knowledge of the flow phenomena occurring in these devices and the large design-space to be explored generally hampers the development of an effective and robust design-procedure. This work investigates the performance of ducted wind turbines through a fully automated analysis procedure based on a Computational-Fluid-Dynamics-Actuator-Disk approach. The method duly takes into account the effects of the design parameters, the rotor-duct coupling, the wake rotation and expansion, and the spanwise variability of the rotor load. A Design-of-Experiment analysis is carried out to quantify the impact of the change of all geometric parameters and their mutual interactions. The latter explicitly account for the simultaneous variation of all design parameters. As such, it is a powerful pre-design tool that allows to reduce and confine the design space. It is found that the chord and stagger angle of the duct contribute more than 85% to the improvements of the turbine performance, while the effects of the thickness are negligible. Finally, the sensitiveness of the performance to the variation of the operating conditions is also analysed revealing that the optimal configuration is also the most robust.