AERODYNAMICS: Part of Fluid Mechanics that is about air.
AEROFOIL: Aerodynamic blade profile.
ASYNCHRONOUS (OR INDUCTION) GENERATOR: The most common generator used in Wind Turbines. Two types, Squirrel Cage Induction Generator (SCIG) or Wound Rotor Induction Generator (WRIG).
DATA LOGGER: Equipment to register automatically the data from the anemometers (wind speed) and the wind vanes (wind direction). Then, the information is transferred to the meteorological institute.
FEATHERED: Position of the rotor’s blades when it is reached the cut-out wind speed. The blades are turned out of the wind so that the wind can blow through the rotor without creating any lift and the rotor stops rotationg.
GEOSTROPHIC WIND: This wind flows at a centain height in the atmosphere where it is just influenced by the Coriolis forces and the pressure gradient forces. It has not got any friction against the Earth’s surface.
INTERNAL BOUNDARY LAYER: Turbulence created when the wind frictions with the terrain.
NEUTRAL CONDITION: When temperature at ground levels is equal to higher ones. It is prone to appear in autumn or in windy days.
POWER COEFFICIENT (CP): The share of the power in the wind that can be utilize by the rotor. Its maximum value is 16/27 (0,593).
POWER CONVERTER: It connects the generator (for variable-speed wind turbines) to the grid. It means, controls the generator speed by absorbing the power fluctuations caused by wind variations.
POWER LAW: Equation to calculate the wind speed at heights bigger than 50 m. [v/v0 = (h/h0)^α] Where: v=wind speed at heigh h. v0=wind speed at heigh h0. α=0,1 if the roughness of the terrain is open water, α=0,15 if it is an open plain, α=0,2 if it is the countryside with farms, and α=3 if there are villages and low forest.
ROTOR: Revolving part of the generator. When it starts to revolver a rotating magnetic field is created.
ROUGHNESS CLASSES: Types of terrains according their roughness. There are 5 classes. Open water is 0, open plain 1, countryside with vegetation and open areas 2, towns and woods 3, large cities or dense forests 4.
SIGNAL-TO-NOISE RATIO (SNR): Used by remote sensing apparatus to compare the level of a desired signal to the level of background noise. A ratio higher than 1:1 indicates more signal than noise.
STABLE CONDITION: When temperature at ground levels is lower than higher ones. It is prone to appear in winter or at night. In this situation, there are less turbulences it the atmosphere and this means that vertical energy transport is less effective.
STALL: Angle which doesn’t allow lift forces on the aerofoil because whirls are created.
STATOR: Stationary part of the generator.
TIP SPEED RATIO (λ): Measure of the relation between the tip speed (the speed of the tip of the rotor blades) and the undisturbed wind speed (before it has been retarded by the rotor).
UNSTABLE CONDITION: When temperature at ground levels is higher than higher ones. It is prone to appear in summer or day times. In this situation, there are more turbulences it the atmosphere and this means that vertical energy transport is more effective.
VOLTAGE FREQUENCY DEVIATION: Difference between the frequency caused by any mismatch between generation and demand.
WEIBULL DISTRIBUTION: It is a continuous probability distribution used to calculate the Wind Energy in a place. It is a factor you must multiple to the formula E= ½ρAv3 . Usually, it is close to 2.
WIND GRADIENT (WIND PROFILE): Relation between wind speed and height. (See Power Law.)
WIND ATLAS METHOD: Empirical method to calculate the wind energy at different sites developed in 1980’s in Risoe (Demark). It can be used with computer programs WAsP, WindPRO, WindFarm and WindFarmer.
WIND WAKE: Strong turbulence created when the wind passes through the rotor of a turbine. This whirling wind influences the wind speed up to a distance of 10 rotor diameter or more behind the turbine.