Open Journal of Fluid Dynamics, 2017, 7, 105-129 http://www.scirp.org/journal/ojfd ISSN Online: 2165-3860 ISSN Print: 2165-3852 DOI: 10.4236/ojfd.2017.71008 March 30, 2017 Effects of Inflow Conditions on Wind Turbine Performance and near Wake Structure Mubashar Khan 1 , Ylva Odemark 2 , Jens H. M. Fransson 1,3 1 Energy Systems, University of Gävle, Gävle, Sweden 2 Vattenfall AB, Stockholm, Sweden 3 Department of Mechanics, Royal Institute of Technology, Stockholm, Sweden Abstract Knowledge about the structure and development of wakes behind wind tur- bines 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 measure- ments 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 dif- ferent distributions of the streamwise and vertical components of the turbu- lence 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 in- let turbulence, while the case with higher inlet turbulence developed a differ- ent distribution of vortices in the wake. Keywords Wind Turbine Model, Wake Structure, Tip Vortex, Turbulence Mixing, Particle Image Velocimetry 1. Introduction The turbulent wake behind a horizontal axis wind turbine is mainly charac- terized by a helical system of tip vortices, a mean velocity deficit and a tur- bulence distribution. The low velocity and high turbulence levels in the wake How to cite this paper: Khan, M., Ode- mark, Y. and Fransson, J.H.M. (2017) Ef- fects of Inflow Conditions on Wind Tur- bine Performance and near Wake Struc- ture. Open Journal of Fluid Dynamics, 7, 105-129. https://doi.org/10.4236/ojfd.2017.71008 Received: February 23, 2017 Accepted: March 27, 2017 Published: March 30, 2017 Copyright © 2017 by authors and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access