The wake behind paired Savonious turbines: a characterization for an optimal spatial distribution in urban milieus.

The use of vertical axis wind turbines (VAWTs) for “green” and on-site energy production in urban environments is a promising strategy receiving noticeable interest in academic and industrial contexts. Despite this, the main shortcoming of VAWTs is their low efficiency which can be improved by placing arrays of two or more turbines nearby, in turn resulting in challenges related to the aerodynamic interactions between them. Therefore, more experimental characterization is required to elucidate the interrelations between the turbine’s wakes and thus get an optimal spatial distribution. Addressing these issues, we measure the velocity in the wakes of two Savonius turbines positioned at various lateral distances in a wind tunnel. Power measurements are also conducted to assess the turbines’ performance, comparing with the isolated case, in the different configurations tested corresponding to different tip-speed ratios, shaft-to-shaft lateral spacing (H), and directions of rotation. We found that small variations in H (from 1.4 to 1.8 times the turbine’s diameter) produce a significant reduction in the turbulence level in the wakes and a momentum enhancement around the turbines. The co-rotating configuration exhibits the most significant variations in terms of power when H changes, and the inwards counter-rotating case displays the smallest turbulent wake. Thus, these results provide a guide for an optimal spatial distribution of the turbines in small spaces like those typically found in urban milieus.