High Reynolds number wind turbine blade equipped with root spoilers. Part I: Unsteady aerodynamic analysis using URANS simulations

Abstract

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.

High Reynolds number wind turbine blade equipped with root spoilers. Part II: Impact on energy production and turbine lifetime

“…To overcome the single steady polar limitation and use the unsteady coefficient, we decided to generate three steady polars corresponding to the mean, minimum, and maximum C L , C D and C M for each turbine case: "no spoiler" and "spoiler" 75 (see Table 1). Those mean, minimum and maximum coefficients are representative of the states reached by the aerodynamic coefficients during the time series calculated using 2D CFD as found in Potentier et al (2021b) (see e.g. Figure 2).…”

“…In Potentier et al (2021b), the authors showed that a VSF can easily be found for a single aerofoil at a single angle of attack using 2D CFD velocity (or load) time series. Applying the same methodology for all aerofoils and for all angles of attack, 2D…”

“…The blade geometry is discretised more densely at the root of the blade since the spoiler is installed at this location. More details about the scan post-treatment are available in Potentier et al (2021b). The scanned blade was originally equipped with root spoilers.…”

“…The procedure described relies on steady polar to perform the iterative steps, it is an inherent BEM limitation. However, as highlighted in Potentier et al (2021b), aerodynamic properties becomes highly unsteady at the blade root when a spoiler is present. To overcome the single steady polar limitation and use the unsteady coefficient, we decided to generate three steady polars corresponding to the mean, minimum, and maximum C L , C D and C M for each turbine case: "no spoiler" and "spoiler" 75 (see Table 1).…”

“…One of the remaining challenge to predict even more accurately the turbine loads is to account for the local unsteadiness, self generated by the flow travelling around an aerofoil, that can be interacting with large scale unsteadiness. As detailed in Potentier et al (2021b), where thick blade profiles equipped with blade root AAO were studied with 2D CFD with low turbulence intensity free stream condition; the spoiler produces the desired higher lift by reorganising the flow and pressure distribution around the aerofoil. In consequence the unsteady behaviour (vortex shedding) behind the aerofoil is vastly different from the bare blade.…”