Influence of incoming turbulence and shear on the flow field and performance of a lab-scale roof-mounted vertical axis wind turbine

Abstract

Flow conditions in an urban environment are complex, featuring varying levels of turbulence intensity and shear. The influence of these flow characteristics on the performance of a roof-mounted vertical axis wind turbine of the Savonius (drag) type is investigated at lab scale. Five different inflow conditions are generated with an active grid in a wind tunnel, covering turbulence intensities from 0.9% to 11.5% and relative vertical shear from 0% to 17%. The flow field is captured using particle image velocimetry, and the power output of the turbine is assessed through measurements of the converted power. The set-up consists of two-surface mounted cubes aligned with each other in the main flow direction, spaced apart by two cube heights. The turbine is placed on top of these model buildings at six different streamwise positions along the centerline and at two different heights. It was observed that the turbulence intensity in the inflow has a significant impact on the flow field and also on the power output of the turbine. The increasing turbulence intensity leads to smaller regions of recirculating flow. Thus, the turbine experiences higher flow velocities, which is reflected in the measured power. The influence of shear is comparably small on both the flow field and the turbine performance. The higher of the two turbine positions yields higher power output overall. Furthermore, it was shown that the impact of the turbine on the flow field is significant for all inflow conditions and can vary substantially depending on the inflow.