WIND ENGINEERING VOLUME 37, NO. 6, 2013 PP 617-636 617 Effects of Wind Turbine Rotor Modelling on Nacelle Anemometry Khaled Ameur* and Christian Masson* Ph.D candidate Email: k-ameur@hotmail.com Professor Research Laboratory on Nordic Environment Aerodynamics of Wind Turbines Email: Christian.Masson@etsmtl.ca Received: November 06, 2012; Revised: September 09, 2013; Accepted: September 26, 2013 ABSTRACT A numerical analysis of the flow near the nacelles of two wind turbines is performed through 3D RANS simulations with the k -ω sst turbulence model. The rotor is modeled using three approaches:two techniques based on the actuator disk and one based on the actuator line. The effects of the rotor representation on the predicted flow at the location of the nacelle anemometer are quantified. In general, agreement with measurements is better for the actuator line than the actuator disk which tends to underestimate the wind speed in the very near wake. At low wind speeds, the three rotor modelling techniques predict nearly identical nacelle transfer functions; differences appear at higher wind speed where the the actuator line is slightly better compared to the other techniques. Keywords: Wind turbine, 3D RANS, actuator disk, actuator line, turbulence modelling, nacelle anemometry, nacelle transfer function. 1. INTRODUCTION Determination of the free stream wind speed (FSWS) at the location of a wind turbine is crucial to constructing its power curve and thus identifying any problems related to low energy production. The draft document IEC61400-12-2 [1] recommends using nacelle anemometry to estimate the FSWS based on the measured wind speed of the nacelle- mounted anemometer. This is an especialy attractive method as no meteorological mast is needed [2–4]. However, it requires the relationship, known as the Nacelle Transfer Function (NTF), between the FSWS and the Nacelle Wind Speed (NWS) to be known. To build this relationship, it is important to consider the structure of the very near wake, where vortices shed from root blade could interact with the nacelle. Within the framework of Reynolds-Averaged Navier-Stokes (RANS) simulations, the most complete numerical simulation of the flow around a wind turbine should consider all length scales, including those of the atmospheric surface layer and the blade and nacelle boundary layers. In such simulations, the blade, nacelle, tower and ground are completely described in the computational domain. Such an approach is very expensive since it requires a large number of cells to form the grid and the consideration of blade rotation in a fixed reference *École de technologie supérieure, Département de génie mécanique, 1100 Notre-Dame Ouest, Montréal, Québec, H3C 1K3, Canada.