Wake effect model

In WAsP, as well as in the old Park DOS-program from which the algorithm was derived, the calculation of mutual wake effects between the turbines in a wind farm is based on a model described in the following paper from the EWEA 1986 conference:

I. Katic, J. Højstrup and N.O. Jensen: "A Simple Model for Cluster Effeciency", European Wind Energy Association Conference and Exhibition, 7-9 October 1986, Rome, Italy.

The flow field used by the model to calculate wind turbine output is indicated below.

The effective wind speed deficit at the down-wind wind turbine ("1") is calculated using the following equation

U0 is the undisturbed wind speed at the up-wind turbine ("0") with rotor diameter D0, Ct the thrust coefficient, X01 the downwind horizontal distance between the wind turbines and k is the wake decay constant.

The thrust coefficient Ct is related to the thrust force FT, rho being the density of the air, as

The initial wind speed reduction from U0 to V, when passing the rotor plane, is related to Ct by: (1-Ct) = (V/U0)2.

The wake effect decay constant has the default value = 0.075 which according to our experience is adequate in most land-cases. In off-shore applications, however, we recommend to use a lower limit of k = 0.04.

  • predicted wind climates + WTG characteristics + wind farm layout —> wind farm wake losses