Aerodyanamics of Horizontal Wind Turbines

The horizontal wind turbine types of blades are usually made of two or three airfoils such as a propeller. In these types of blades, it is the lift force which makes the rotor turn. As shown in figure 4, when the wind hits the airfoil, the wind gets separated into two. It will pass over the top and the bottom side of the airfoil. Since the top distance is longer, the wind velocity will increase, therefore creating lower pressure on the top of the airfoil. The lower portion will therefore have a higher pressure than the top of the airfoil and this difference in pressure will result in the force known as the lift.

Principles of HAWT Aerodynamic Lift

The lift force can be calculated from the following equation:

L=1/2ρV^2ACL

Where
ρ=Density of air [kg/m^3]
V=Velocity of the wind [m/s]
A=Surface area [m^2]
CL=Lift coefficient

The drag force acts perpendicular to the lift force due to the resistance of the airfoil from the wind and would counteract the rotation to rotor. The higher the lift-to-drag ratio, the higher the torque output would be for the wind turbine.