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Chapter 6
Wind Turbine Airfoils and Rotor Wakes

Excerpt

In this chapter we will discuss the detailed characteristics of the lifting surfaces which we know as airfoils, in order to provide guidance in the selection of airfoil shapes that will perform satisfactorily over the broad operating environment of a wind turbine. In addition, the fundamental fluid-dynamic principles involved in modeling the structure of rotor wakes and integrating wake-induced effects over an array of turbines are presented in this chapter.

Wind turbines operate by the action of the relative wind (the natural wind plus wind caused by rotor motion and rotor-induced flow), which creates aerodynamic forces on the rotating blades. These can normally be grouped into lift-like forces and drag-like forces. Lift forces operate through the generation of circulation and do not involve large viscous losses in the flow and the associated loss of total head, while drag forces function through flow separation on the blade and the loss of total head. In the previous chapter, the relative merits of lift and drag power devices were discussed, with lift being the clear preference for wind turbine rotors. When considering the potential impact of wakes on the total output of a wind power station, a lift-type device is again preferred, since a drag-type unit develops a greater wake and less energy is available to downwind units. Thus, the array efficiency of a cluster of drag-type units will be lower than that of lift-type turbines.

  • Introduction
  • Characteristic Behavior of Airfoils
  • Airfoil Aerodynamic Requirements
  • Airfoil Selection
  • Field Performance Testing of Wind Turbine Airfoils
  • Tip Shapes of HAWT Blades
  • Wind Turbine Wake Effects
  • Development of Wind Turbine Wake Models
  • Wake Geometry Models
  • Integration of Wakes for Array Effect
  • Analytical Results Obtained with Wake Models
  • Measurement of Wake Effects
  • Summary Comments on Wind Turbine Wake Effects
  • References

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