Laboratory investigation of the near and intermediate wake of a wind turbine at very high Reynolds numbers

The wake of a horizontal-axis wind turbine (HAWT) is investigated at very high Reynolds numbers, through a set of unique laboratory experiments. Well-resolved measurements of the axial component of velocity are performed using nano-scale hot-wire anemometry. The experiments were conducted at Reynolds numbers, based on the model diameter and free stream velocity, from 2.7 × 10^6 to 7.2 × 10^6 , significantly higher than most previous laboratory studies. Measurements were acquired at five different downstream positions in the range of 0.77 to 5.52 diameters. It is shown that the Reynolds number effects on both the mean and fluctuating velocity fields are minor, and that the mean velocity exhibits self-similar behavior, but the variance does not. Analyses of the variance profiles, at different axial locations, are used to identify discrete tip vortices, and their locations, as well as an annular shear layer in the wake core rather than discrete root vortices. The existence of these structures is verified with phase averaged results. Graphical abstract