Simple turbine wake models depend on the thrust and the turbulence level at the turbine. The thrust is the downwind loading on the turbine and this force converts directly into a loss of momentum (or speed) in the wake. The turbulence information in contained in the on-site measured wind rose data.
The wake from one turbine will be detrimental on the wind speed and turbulence at down wind turbines. The effects of the wake spread out downwind and decay with distance according to generalised wake models. In practice a minimum physical separation between wind turbines of 3 to 4 diameters is usually specified . Smaller separations introduce additional uncertainty in the wake loss calculations.
More complex wake models using full incompressible flow models and Large Eddy Simulation techniques are available from Wind Measurement International.