Articles | Volume 1, issue 2
Wind Energ. Sci., 1, 89–100, 2016
Wind Energ. Sci., 1, 89–100, 2016

Research article 12 Jul 2016

Research article | 12 Jul 2016

Detailed analysis of the blade root flow of a horizontal axis wind turbine

Iván Herráez1, Buşra Akay2, Gerard J. W. van Bussel2, Joachim Peinke1,3, and Bernhard Stoevesandt3 Iván Herráez et al.
  • 1ForWind, Institute of Physics, University of Oldenburg, 26111, Oldenburg, Germany
  • 2Wind Energy Research Group, Faculty of Aerospace Engineering, Delft University of Technology, Kluijverweg 1, 2629HS Delft, the Netherlands
  • 3Fraunhofer Institute for Wind Energy and Energy System Technology (IWES), Ammerländer Heerstr. 136, Oldenburg, Germany

Abstract. The root flow of wind turbine blades is subjected to complex physical mechanisms that influence significantly the rotor aerodynamic performance. Spanwise flows, the Himmelskamp effect, and the formation of the root vortex are examples of interrelated aerodynamic phenomena that take place in the blade root region. In this study we address those phenomena by means of particle image velocimetry (PIV) measurements and Reynolds-averaged Navier–Stokes (RANS) simulations. The numerical results obtained in this study are in very good agreement with the experiments and unveil the details of the intricate root flow. The Himmelskamp effect is shown to delay the stall onset and to enhance the lift force coefficient Cl even at moderate angles of attack. This improvement in the aerodynamic performance occurs in spite of the negative influence of the mentioned effect on the suction peak of the involved blade sections. The results also show that the vortex emanating from the spanwise position of maximum chord length rotates in the opposite direction to the root vortex, which affects the wake evolution. Furthermore, the aerodynamic losses in the root region are demonstrated to take place much more gradually than at the tip.

Short summary
The flow in the blade root region of horizontal axis wind turbines is highly three-dimensional. Furthermore, it is influenced by the presence of strong trailing vortices. In this work we study the complex root flow by means of experiments and numerical simulations. The simulations are shown to be reliable at predicting the main flow features of the rotor blades. Additionally, new insight into the physical mechanisms governing the blade root aerodynamics is given.