Comparison between Wind Tunnel and Field Experiments on Wind Turbine Wake Meandering

Abstract

In order to determine the physics driving the wind turbine wake meandering process [4], a previous study has been performed in an atmospheric boundary layer wind tunnel focusing on the unsteady behaviour of a modelled wind turbine wake (i.e. physical modelling based on the actuator disc concept). It was proven that the presence of turbulent scales larger than the wind turbine diameter could be responsible for a random flapping of the whole wake (i.e. wake meandering) [2]. This is indeed the case in full-scale environments, since the large turbulent scales of the atmospheric boundary layer typically are several hundred meters, whereas the diameter of a modern wind turbine rotor is around one hundred meters. PIV measurements of the scaled wind turbine wakes have been performed, and a specific image processing technique enabled to determine the instantaneous deviations of the wake position from its time-average location, as well as the width of the instantaneous wake. The image processing technique originally applied was based on determination of the wake deficit borders through a velocity threshold applied on the instantaneous velocity fields.