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The wind imparts a torque on the wind turbine, thrust is a necessary by-product of torque. Newtonian physics dictates that for every action there is an equal and opposite reaction. If the wind imparts torque on the blades, then the blades must be imparting torque on the wind.
This means that as the wind speed changes, the rotor speed must change as well such that C p = C p max. A wind turbine with a variable rotor speed is called a variable-speed wind turbine. Whilst this does mean that the wind turbine operates at or close to C p max for a range of wind speeds, the frequency of the AC voltage generator will not be ...
According to Betz's law, no wind turbine of any mechanism can capture more than 16/27 (59.3%) of the kinetic energy in wind. The factor 16/27 (0.593) is known as Betz's coefficient. Practical utility-scale wind turbines achieve at peak 75–80% of the Betz limit. [2] [3] The Betz limit is based on an open-disk actuator.
When rotor power or torque coefficient is assumed constant, the weighing function is: = and the corresponding weighted solidity ratio is known as the power or torque-weighted solidity ratio. This solidity ratio is analogous to the activity factor used in propeller design and is also used in wind turbine analysis.
The power coefficient is a representation of how much of the available power in the wind is captured by the wind turbine and can be looked up in the graph above. The torque, Q {\displaystyle Q} , on the rotor shaft is given by the ratio of the power extracted to the rotor speed:
Whereas the streamtube area is reduced by a propeller, it is expanded by a wind turbine. For either application, a highly simplified but useful approximation is the Rankine–Froude "momentum" or "actuator disk" model (1865, [1] 1889 [2]). This article explains the application of the "Betz limit" to the efficiency of a ground-based wind turbine.
The advance ratio is the inverse of the tip speed ratio, , used in wind turbine aerodynamics: [6] μ = λ − 1 {\displaystyle \mu =\lambda ^{-1}} . In operation, propellers and rotors are generally spinning, but could be immersed in a stationary fluid.
An example of a wind turbine, this 3 bladed turbine is the classic design of modern wind turbines Wind turbine components : 1-Foundation, 2-Connection to the electric grid, 3-Tower, 4-Access ladder, 5-Wind orientation control (Yaw control), 6-Nacelle, 7-Generator, 8-Anemometer, 9-Electric or Mechanical Brake, 10-Gearbox, 11-Rotor blade, 12-Blade pitch control, 13-Rotor hub