Effects of Upstream Buildings on the Performance of a Synergistic Roof-and-Diffuser Augmentation System for Cross Flow Wind Turbines

In a previous work we investigated the effectiveness of combining the concentration effects generated by a dual-pitched roof and a convergent-divergent semi-diffuser placed over a cross flow turbine (CFT), which is rooftop mounted with horizontal shaft running close to the roof ridge. By means of 2D CFD we now assess the effects of the upstream buildings on the performance of this concentration system. Three different urban layouts are simulated via a challenging fully-resolved URANS approach that gives unprecedented insight into the complex interactions of the flow around buildings, diffuser and turbine's blades. A promising power augmentation of 40% with respect to the case without diffuser are obtained and the mechanism behind this performance enhancement are analysed. The beneficial effect of the diffuser on the torque fluctuations damping (similar to 60%) is also discussed. Important remarks on the load control strategy for diffuser-augmented CFT are finally presented.