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

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

Abstract: 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.

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

Cite this paper: Khan, M. , Odemark, Y. , 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.

References

[1]   Vermeer, L.J., Sørensen, J.N. and Crespo, A. (2003) Wind Turbine Wake Aerodynamics. Progress in Aerospace Sciences, 39, 467-510. https://doi.org/10.1016/S0376-0421(03)00078-2

[2]   Zhang, W., Markfort, C.D. and Porté-Agel, F. (2012) Near-Wake Flow Structure Downwind of a Wind Turbine in a Turbulent Boundary Layer. Experiments in Fluids, 52, 1219-1235.
https://doi.org/10.1007/s00348-011-1250-8

[3]   Zhang, W.W., Markfort, C.D. and Porté-Agel, F. (2013) Wind-Turbine Wakes in a Convective Boundary Layer: A Wind Tunnel Study. Boundary-Layer Meteorology, 146, 161-179.
https://doi.org/10.1007/s10546-012-9751-4

[4]   Chamorro, L.P. and Porté-Agel, F. (2010) Effects of Thermal Stability and Incoming Boundary-Layer Flow Characteristics on Wind-Turbine Wakes: A Wind-Tunnel Study. Boundary-Layer Meteorology, 136, 515-533. https://doi.org/10.1007/s10546-010-9512-1

[5]   Hu, H., Yang, Z. and Sarkar, P. (2012) Dynamic Wind Loads and Wake Characteristics of a Wind Turbine Model in an Atmospheric Boundary Layer Wind. Experiments in Fluids, 52, 1277-1294. https://doi.org/10.1007/s00348-011-1253-5

[6]   Chamorro, L.P. and Porté-Agel, F. (2009) A Wind-Tunnel Investigation of Wind-Turbine Wakes: Boundary-Layer Turbulence Effects. Boundary-Layer Meteorology, 132, 129-149.
https://doi.org/10.1007/s10546-009-9380-8

[7]   Snel, H., Schepers, J.G. and Montgomerie, B. (2007) The MEXICO Project (Model Experiments in Controlled Conditions): The Database and First Results of Data Processing and Interpretation. Journal of Physics: Conference Series, 75, Article ID: 012014.
https://doi.org/10.1088/1742-6596/75/1/012014

[8]   Medici, D. and Alfredsson, P.H. (2006) Measurements on a Wind Turbine Wake: 3D Effects and Bluff body Vortex Shedding. Wind Energy, 9, 219-236. https://doi.org/10.1002/we.156

[9]   Odemark, Y. (2012) Wakes behind Wind Turbines—Studies on Tip Vortex Evolution and Stability. Licentiate Thesis, KTH Royal Institute of Technology, Stockholm.

[10]   Chamorro, L.P., Arndt, R.E.A. and Sotiropoulos, F. (2012) Reynolds Number Dependence of Turbulence Statistics in the Wake of Wind Turbines. Wind Energy, 15, 733-742.
https://doi.org/10.1002/we.501

[11]   Chamorro, L.P., Guala, M., Arndt, R.E.A. and Sotiropoulos, F. (2012) On the Evolution of Turbulent Scales in the Wake of a Wind Turbine Model. Journal of Turbulence, 13, 1-13.
https://doi.org/10.1080/14685248.2012.697169

[12]   Crespo, A. and Hernández, J. (1996) Turbulence Characteristics in Wind-Turbine Wakes. Journal of Wind Engineering and Industrial Aerodynamics, 61, 71-85.
https://doi.org/10.1016/0167-6105(95)00033-X

[13]   Adaramola, M.S. and Krogstad, P. (2011) Experimental Investigation of Wake Effects on Wind Turbine Performance. Renewable Energy, 36, 2078-2086.
https://doi.org/10.1016/j.renene.2011.01.024

[14]   Cal, R.B., Lebrón, J., Castillo, L., Kang, H.S. and Meneveau, C. (2010) Experimental Study of the Horizontally Averaged Flow Structure in a Model Wind-Turbine Array Boundary Layers. Journal of Renewable and Sustainable Energy, 2, Article ID: 013106.
https://doi.org/10.1063/1.3289735

[15]   Glauert, H. (1935) Airplane Propellers. In: Durand, W.F., Ed., Aerodynamic Theory, Springer Verlag, Berlin. https://doi.org/10.1007/978-3-642-91487-4_3

[16]   Burton, R.J., Sharpe, D., Jenkins, N. and Bossanyi, E. (2011) Wind Energy Handbook. John Wiley & Sons, Hoboken. https://doi.org/10.1002/9781119992714

[17]   Wilson, R.E. (1994) Aerodynamic Behaviour of Wind Turbines. In: Spera, D.A., Ed., Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering, ASME Press, New York, 215-282.

[18]   Metzger, M.M. and Klewicki, J.C. (2001) A Comparative Study of Near-Wall Turbulence in High and Low Reynolds Number Boundary Layers. Physics of Fluids, 13, 692-701.
https://doi.org/10.1063/1.1344894

[19]   Manwell, J.F., McGowan, J.G. and Rogers, A.L. (2009) Wind Energy Explained, Theory, Design and Application. Wiley, Hoboken. https://doi.org/10.1002/9781119994367

[20]   Fallenius, B.E.G. (2009) A New Experimental Setup for Studies on Wake Flow Instability and Its Control. Licentiate Thesis, KTH Royal Institute of Technology, Stockholm.

[21]   Fallenius, B.E.G. (2011) Experimental Design and Vortex Analyses in Turbulent Wake Flows. PhD Thesis, KTH Royal Institute of Technology, Stockholm.

[22]   Chong, M.S., Perry, A.E. and Cantwell, B.J. (1990) A General Classification of Three-Dimensional Flow Fields. Physics of Fluids, 2, 765-777. https://doi.org/10.1063/1.857730