Nevertheless, to keep lowering the levelised cost of energy (LCoE), onshore turbines need to produce more energy within the same swept area. Wind energy, over the last decades, increased its market share thanks to longer blades and a continuous increase in rated power. A dominant peak frequency is emerging in the aerodynamic polar coefficients, when adding a spoiler, which corresponds to a vortex shedding organisation. Another drawback of the spoiler addition is the unsteady effects. 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. Using the wall pressure distributions and the associated spatio-temporal organisation of the flow field, those fluctuations are well characterised. The spoiler induces an important wake behaviour linked to the apparition of global load fluctuations.
Analyses are then continued accounting for the flow unsteadiness. 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.
Comparing to existing literature, it is at least 1 order of magnitude larger than the size of the well-known Gurney flaps. The analysed spoiler is of commercial size with a height of approximately 33 % of the local chord. Computations were performed at the chord-based Reynolds number R e c = 3 × 10 6. 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. 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.
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