A numerical investigation of nacelle anemometry for a HAWT using actuator disc and line models in CFX

In order to control a horizontal axis wind turbine (HAWT) in an optimal manner, one needs accurate measurements of the oncoming wind conditions. The method currently used by large wind power manufacturers is to measure wind speed and direction on top of the nacelle behind the rotor. In order for such measurements to give correct readings, a correction for the effect of rotor disturbance on the oncoming wind field is needed. This requires use of so-called nacelle transfer functions (NTF). An NTF is an empirical function that relates the undisturbed wind field to the measured wind speed and direction at the nacelle. Currently, the NTF is obtained through a series of costly and time consuming field measurement campaigns. The use of numerical methods, such as the one presented in this article, could both reduce the time needed to acquire an NTF and provide a means to improve NTF accuracy.