Typically, the only area of a wind turbine blade used in the calculation of drag is the front area (leading edge) of the blade.ĭesign engineers aim for the smallest amount of drag. This force is made as little as possible so that as much of the lift as possible can go into useful work (turning the turbine).ĭrag is expressed in terms of the drag coefficient, which is a dimensionless number. The drag force is friction caused by air, which opposes the motion. The motion of the blades is opposed by the force required to spin the generator, friction in the system, and drag. The lift force rotates with the blades so it constantly changes direction. A small portion of this force goes toward turning the blade. The rotation of the blade causes a lift force that is perpendicular to the apparent wind direction. As the blade turns, air that flows across the leading edge appears as a separate component of the wind thus, the apparent wind direction is shifted to oppose the direction of rotation. In this case, lift is shown related to the airflow rather than the wing, as would be the case for an airplane wing.Īssume the flat part of the blade is facing the true wind. In a wind turbine, the term lift is a bit of a misnomer because it does not lift the blade rather, it is a force exerted in a direction that is perpendicular to the apparent wind direction rather than the true direction. For an airplane wing, it is the force that lifts the plane, hence the term lift. Lift is a component of an aerodynamic force exerted on a body that is perpendicular to a fluid (such as air) flowing past it. This force tends to bend the blades and create a smaller rotational force. (b) A lift force is created by pressure differences that are perpendicular to the apparent wind direction. (a) The rounded leading edge is oriented in the direction of rotation. The front of the blade is referred to as the leading edge and the back is referred to as the trailing edge, as illustrated in Figure 1a.įigure 1 Air Moving Past a Turbine. In normal operation, the rounded front portion of the blades is oriented in the direction of rotation and the flat portion faces the wind. Differences in pressure cause the blades to both bends and rotate. This section introduces you to important concepts about turbine blades.Ī turbine blade is similar to a rotating wing. The blade on a wind turbine can be thought of as a rotating wing, but the forces are different on a turbine due to the rotation.
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