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.In this article, two different numerical models based on actuator disc and line techniques are implemented in Ansys CFX. The models are benchmarked against the Blade Element Momentum model (BEM) and against field measurements taken at the nacelle anemometer location of a Vestas V90 turbine. The overall agreement between the CFX actuator models and the reference data sources is found to be very satisfactory. The conclusion of the study is that the proposed models, in their current form, are suitable tools for research and development activities targeting nacelle anemometry or near wake aerodynamics. With some further development to include inflow turbulence and non-axial induction, the models have the potential to be used for generating a numerical NTF.

► The nacelle anemometry of wind turbines studied using two reduced-order CFD models.
► The models are based on actuator representation of the rotor via volume forces.
► The performance of the models is validated against BEM and full scale field data.
► The models are suitable for R&D activities targeting nacelle anemometry and NTF.