- Vertical axis wind turbine
Vertical-axis wind turbines (VAWT) are a type of
wind turbinewhere the main rotor shaft runs vertically. Among the advantages of this arrangement are that generators and gearboxes can be placed close to the ground, and that VAWT do not need to be pointed into the wind. Major drawbacks for the early designs (savonius, darrieus, giromilland cycloturbine) included the pulsatory torquethat can be produced during each revolution and the huge bending moments on the blades. Later designs like turby, quietrevolution and aerotecture solved the torque issue by using the helical twist of the blades, similar to Gorlov's water turbines.
Drag-type VAWT, such as the Savonius rotor, typically operate at lower tipspeed ratios than lift-based VAWT such as Darrieus rotors and cycloturbines.
The forces and the velocities acting in a Darrieus turbine are depicted in figure 1. The resultant velocity vector, , is the vectorial sum of the undisturbed upstream air velocity, , and the velocity vector of the advancing blade, .
Thus, the oncoming fluid velocity varies, the maximum is found for and the minimum is found for , where is the azimutal or orbital blade position. The
angle of attack, , is the angle between the oncoming air speed,W, and the blade's chord. The resultant airflow creates a varying, positive angle of attack to the blade in the upstream zone of the machine which switch sign in the downstream zone of the machine. From geometrical considerations, the resultant airspeed flow and the incidence angle are calculated as follows:
where is the
tip speed ratioparameter.
The resultant aerodynamic force is decomposed either in lift (L) - drag (D) components or normal (N) - tangential (T) components. The forces are considered acting at 1/4 chord from the leading edge, in order to minimise the
pitching moment. The aeronautical terms lift and drag are, strictly speaking, forces across and along the approaching net relative airflow respectively. The tangential force is acting along the blade's velocity and, thus, pulling the blade around, and the normal force is acting radially, and, thus, is acting against the bearings. The lift and the drag force are useful when dealing with the aerodynamic behaviour around each blade, i.e. dynamic stall, boundary layer, etc; while when dealing with global performance, fatigue loads, etc., it is more convenient to have a normal-tangential frame. The lift and the drag coefficients are usually normalized by the dynamic pressure of the relative airflow, while the normal and the tangential coefficients are usually normalized by the dynamic pressure of undisturbed upstream fluid velocity.
Wikimedia Foundation. 2010.
Look at other dictionaries:
Vertical-Axis Wind Turbine — (VAWT) A type of wind turbine in which the axis of rotation is perpendicular to the wind stream and the ground … Energy terms
Vertical-axis wind turbine — (VAWT) A type of wind turbine in which the axis of rotation is perpendicular to the windstream and the ground. U.S. Dept. of Energy, Energy Information Administration s Energy Glossary … Energy terms
Wind turbine — Offshore wind farm using 5MW turbines REpower 5M in the North Sea off Belgium This article discusses wind powered electrical generators. See windmill for wind powered machinery used to grind grain or pump water. A wind turbine is a device that… … Wikipedia
Wind turbine design — An example of a wind turbine, this 3 bladed turbine is the classic design of modern wind turbines Wind turbines History Design … Wikipedia
Darrieus wind turbine — Fig. 1: A Darrieus wind turbine once used to generate electricity on the Magdalen Islands The Darrieus wind turbine is a type of vertical axis wind turbine (VAWT) used to generate electricity from the energy carried in the wind. The turbine… … Wikipedia
Savonius wind turbine — Savonius wind turbines are a type of vertical axis wind turbine (VAWT), used for converting the power of the wind into torque on a rotating shaft. They were invented by the Finnish engineer Sigurd J. Savonius in 1922. Johann Ernst Elias Bessler… … Wikipedia
Airborne wind turbine — An airborne wind turbine is a design concept for a wind turbine that is supported in the air without a tower. [cite web | title=Windmills in the Sky | work=Wired News: Windmills in the Sky | author=David Cohn | publisher=San Francisco: Wired News … Wikipedia
Nacelle (wind turbine) — Components of a horizontal axis wind turbine (gearbox, rotor shaft and brake assembly) being lifted into the nacelle … Wikipedia
Small wind turbine — Small wind turbines may be as small as a fifty watt generator for boat or caravan use. Small units often have direct drive generators, direct current output, aeroelastic blades, lifetime bearings and use a vane to point into the wind. Larger,… … Wikipedia
Turby wind turbine — The Turby is a brand of vertical axis Darrieus wind turbine. The three vertical aerofoil blades have a helical twist of 60 degrees, similar to Gorlov s water turbines . Since the wind pulls each blade around on both the windward and leeward sides … Wikipedia