Abstract. A wind turbine blade equipped with root spoilers is analysed using 2D Computational Fluid Dynamics (CFD) to assess the unsteady impact of passive devices. Several metrics such as lift and drag coefficients, pressure and instantaneous velocity field around the aerofoil, Power Spectral Density and Strouhal number are used in the 2D unsteady analysis. The spoiler is found to efficiently rearrange the flow, adding lift throughout the positive angles of attack. However, the drawback is a high drag penalty coupled with high unsteadiness of the aerodynamic forces.

Abstract. A commercial wind turbine blade equipped with root spoilers is analysed using 2D URANS computational fluid dynamics (CFD) to assess the unsteady impact of passive devices. In this work, we present the 2D CFD unsteady results from a non-rotating single thick section located at the root end of the blade with and without spoiler. Computations were performed at the chord-based Reynolds number Rec=3×106. The analysed spoiler is of commercial size with a height of approximately 33 % of the local chord. Comparing to existing literature, it is at least 1 order of magnitude larger than the size of the well-known Gurney flaps. The analysis is first performed in the steady state at a single angle of attack using global aerodynamic forces, the local pressure distributions, and flow field analysis. Analyses are then continued accounting for the flow unsteadiness. The spoiler induces an important wake behaviour linked to the apparition of global load fluctuations. Using the wall pressure distributions and the associated spatio-temporal organisation of the flow field, those fluctuations are well characterised. Globally, in terms of lift gain, adding a spoiler is found to be detrimental for the negative angles of attack while of high interest for higher angles of attack. Another drawback of the spoiler addition is the unsteady effects. A dominant peak frequency is emerging in the aerodynamic polar coefficients, when adding a spoiler, which corresponds to a vortex shedding organisation.

Abstract. A wind turbine blade equipped with root spoilers is analysed using time domain aeroelastic blade element momentum (BEM) simulations to assess the impact of passive devices on the turbine annual energy production (AEP) and lifetime. Previous 2D computational fluid dynamics (CFD) showed a large unsteadiness in aerodynamic coefficients associated with the spoiler, and such behaviour is captured by the OpenFAST simulations when all degrees of freedom are switched off. Once the turbine is fully flexible, a novel way to account for aerofoil-generated unsteadiness in the fatigue calculation is proposed and detailed. The outcome shows that spoilers, on average, can increase the AEP of the turbine. However, the structural impacts on the turbine can be severe if not accounted for initially in the turbine design.