Author(s)

Mubashar Khan¹, Ylva Odemark², Jens H. M. Fransson^1,3

¹Energy Systems, University of Gävle, Gävle, Sweden.
²Vattenfall AB, Stockholm, Sweden.
³Department of Mechanics, Royal Institute of Technology, Stockholm, Sweden.

Knowledge about the structure and development of wakes behind wind turbines is important for power optimization of wind power farms. The high turbulence levels in the wakes give rise to undesired unsteady loadings on the downstream turbines, which in the long run might cause fatigue damages. In the present study, the near wake behind a small-scale model wind turbine was investigated experimentally in a wind tunnel. The study consists of measurements with particle image velocimetry using two different inlet conditions: a freely developing boundary layer, causing an almost uniform inflow across the rotor disc, and an inflow with strong shear across the rotor disc, in order to model the atmospheric boundary layer. The results show a faster recovery of the wake in the case with shear inflow, caused by the higher turbulence levels and enhanced mixing of momentum. The increased inlet turbulence levels in this case also resulted in a faster breakdown of the tip vortices as well as different distributions of the streamwise and vertical components of the turbulence intensity in the wake. An analysis comparing vortex statistics for the two cases also showed the presence of strong tip vortices in the case with lower inlet turbulence, while the case with higher inlet turbulence developed a different distribution of vortices in the wake.

Wind Turbine Model, Wake Structure, Tip Vortex, Turbulence Mixing, Particle Image Velocimetry

Khan, M. , Odemark, Y. and Fransson, J. (2017) Effects of Inflow Conditions on Wind Turbine Performance and near Wake Structure. Open Journal of Fluid Dynamics, 7, 105-129. doi: 10.4236/ojfd.2017.71008.