Aerodynamics of Wind Turbines: Lift
The rotor consisting of the rotor blades and the hub are placed upwind of the tower and the nacelle on most modern wind turbines. This is primarily done because the air current behind the tower is very irregular (turbulent).
What makes the rotor turn?
The answer seems obvious - the wind.
But actually, it is a bit more complicated than just the air molecules hitting the front of the rotor blades. Modern wind turbines borrow technologies known from aeroplanes and helicopters, plus a few advanced tricks of their own, because wind turbines actually work in a very different environment with changing wind speeds and changing wind directions.
Have a look at the animation of the cut-off profile (cross section) of the wing of an aircraft. The reason why an aeroplane can fly is that the air sliding along the upper surface of the wing will move faster than on the lower surface.
This means that the pressure will be lowest on the upper surface. This creates the lift, i.e. the force pulling upwards that enables the plane to fly.
The lift is perpendicular to the direction of the wind. The lift phenomenon has been well known for centuries to people who do roofing work: They know from experience that roof material on the lee side of the roof (the side not facing the wind) is torn off quickly, if the roofing material is not properly attached to its substructure.
© Copyright 1997-2003 Danish Wind Industry Association
Updated 1 June 2003