Aerodynamic analysis of clustered, diffuser-augmented turbines

The wind turbine industry has seen innovations leading to growing size of turbines of currently over 160 m in diameter. However, as pointed out by some recent studies, up-scaling of blades has its limitations and therefore advantages of multi-rotor system concepts have been suggested by Jamieson et al. The so-called wind lens turbine, which was developed by Kyushu University, shows increased power output using a brimmed diffuser to augment the approaching wind flow. In the presented research we are investigating the aerodynamics of wind lens turbines spaced closely together comprising a multi-rotor system. We placed up to three of these turbines closely in an array perpendicular to the flow and measured power output. The total power output of multiple turbines was then compared to the power of the stand-alone setup. Several different wind lens configurations have been used, mainly varying the brim height. We observed that the performance of the turbines is influenced by the width of the gap between the brims and the brim height of the wind lens configuration. The best performance was at a gap of 0.15 D with 10% brim height which leads to a power increase of more than 9 % in a three turbine side-by-side arrangement. Further it was observed that the individual power output doesn't follow the trend of the cumulative power output. These phenomena can be explained with flow patterns observed in gap flow analysis of bluff bodies. Further research is necessary to fully understand which mechanisms in three dimensional gap flow cause the effect on the performance of the turbines.