Wind turbine wake influence on the mixing of relative humidity quantified through wind tunnel experiments

Abstract

An experimental study conducted in a wind tunnel on the mixing of moist air by a scaled wind turbine is presented. The experimental setup allows us to generate stable stratification conditions with respect to relative humidity and temperature in a closed-loop wind tunnel. The flow and its thermodynamic properties were characterized using a Cobra probe (a multi-hole pitot tube) and a sensor of local temperature and relative humidity, both used simultaneously to obtain vertical profiles. The flow and its stratification were measured downstream of a scaled rotor at two different streamwise distances (1 and 10 rotor diameters) and two Reynolds numbers based on the diameter of the wind turbine rotor (22 000 and 44 000, respectively). This was then compared to the inflow conditions. The wake mean structure and the humidity and temperature stratifications of the flow are found to be affected by the presence of the rotor. In particular, the stratification was always smaller one diameter downstream from the model (when compared to the empty test section case), and then was mostly recovered in the far wake (10 diameters downstream). This effect depended not only on the streamwise distance, but also on the Reynolds number of the flow. Finally, the bulk Richardson number Rb was found to be an appropriate parameter to quantify this effect.