Since a wind turbine generates electricity from the energy in the wind, the wind leaving the turbine must have a lower energy content than the wind arriving in front of the turbine. This follows directly from the fact that energy can neither be created nor consumed.
A wind turbine will always cast a wind shade in the downwind direction.
In fact, there will be a wake behind the turbine, i.e. a long trail of wind which is quite turbulent and slowed down, when compared to the wind arriving in front of the turbine (the expression wake is obviously derived from the wake behind a ship).
The wake trailing behind a wind turbine can be seen, if smoke is added to the air passing through the turbine, as was done in the picture (this particular turbine was designed to rotate in a counterclockwise direction which is somewhat unusual for modern wind turbines).
Wind turbines in parks are usually spaced at least three rotor diameters from one another in order to avoid too much turbulence around the turbines downstream. In the prevailing wind direction turbines are usually spaced even farther apart, as explained in the next page.
- Wake effects: general notes
- Wake velocities for pitch/stall machines: values from BEM, graph
- Measured (nearer) wakes: graphs and notes for spacing
- Wake effects: velocities at 10D behind a turbine
- Wake interference: more graphs, wind farm
- Jensen's (far) wake model: simple model, explanation
- Ainslie wake model: advanced model, explanation