Wind tunnel validation of wind turbine load reducing concepts based on individual pitch control and blades with rigid leading edge slats

Abstract

To enable further increases in wind turbine dimensions, and thus to lower the levelized cost of energy, active and passive concepts for load reduction have to be further developed. One of such concepts is individual pitch control, which has been thoroughly analysed and validated in simulations and experiments (e.g., see [1] and references therein), and is currently used by some modern multi-megawatt wind turbines. On the other hand, although well known from aeronautics, concepts based on rotor blades with trailing edge flaps or leading edge slats have still not found any commercial application in wind energy. One obstacle is seen in the lack of a thorough and convincing validation of such concepts. In this work, we present our wind tunnel setup for experimental validation of advanced concepts for wind turbine load reduction, and analyse the interaction between rigid slats and the wind turbine control system in different inflow conditions. The wind tunnel at the University of Oldenburg has a nozzle of 3 m by 3 m and an active grid, which can impress a wide range of tailored turbulent flow conditions and coherent gusts on the wind flow (see Fig. 1) [2]. The fully controllable and aerodynamically scaled version of a 5 MW reference turbine MoWiTO (Model Wind Turbine Oldenburg) with a rotor diameter of 1.8 m features the measurement of flapwise blade root and tower bending moments, rotor speed, and torque [3]. MoWiTO can be operated with two sets of blades – a set with rigid leading edge slats [4] (see Fig. 1), and a reference set without slats. Additionally, the real-time hardware enables implementation of different control algorithms, but for the purpose of this work, two control algorithms will be used: a baseline controller for torque and collective pitch control, and an individual pitch controller designed to reduce once-per-revolution blade bending moments (see Fig. 1). Using the active grid, the capability of the rigid slats in combination with individual pitch control will be analysed in different inflow conditions, including turbulent and sheared flows, and wind gusts