![]() ![]() Additionally, comparison studies are presented to investigate the impact of airfoil thickness on the frequency content at Re c=2.0×10 6. The effect of varying Rec on the airfoil frequency statistics is investigated. Simulations conducted on the finer spanwise grids demonstrate grid independence and show good agreement with experiments. Based on this study, NACA 0021 airfoil runs are performed with IDDES for Re c=2.7×10 5 and 2.0×10 6 on the finest wall-normal mesh and three spanwise grids. The Strouhal number, based on normalised chord length, remains nearly constant in this region. In the post-stall regime, both lift and drag frequencies drop asymptotically with increasing α. Spectral analysis shows the peak primary shedding frequency at α=30°, which signifies the end of the stall region. Only the IDDES model with a minimum spanwise resolution of 24 cells per chord length correctly predicts the aerodynamic forces. The effect of mesh resolution both in the wall-normal and spanwise directions is investigated. In this context, the NACA 0012 airfoil simulations are conducted at a chord-based Reynolds number, Re c=2×10 6, with the k-ω Shear-Stress Transport Reynolds-Averaged Navier-Stokes (RANS) and Improved Delayed more » Detached Eddy Simulation (IDDES) hybrid RANS-Large Eddy Simulation turbulence models. Accurate predictions of post-stall aerodynamics can identify the frequencies at which such vibrations maybe triggered. At high angles of attack (α), wind turbine blades routinely experience vortex-induced vibrations, which can cause significant structural damages. Here, this work presents a comprehensive computational fluid dynamics investigation of the effects of grid resolution and turbulence-model choice for capturing the unsteady three-dimensional aerodynamic performance of NACA 00 airfoils, with specific focus on the deep-stall regime. Furthermore, the potential benefit of reducing the airfoil drag is clearly illustrated by the presentation of the individual contributions of lift and drag to power. The airfoil shapes considered are the conventional airfoils NACA 0018 and NACA 0021, and the SNLA 0018/50 airfoil designed at Sandia. To achieve this goal, the streamtube model of Paraschivoiu (1988) is used to predict the performance of VAWTs equipped with blades of various airfoil shapes. ![]() This technical brief illustrates the benefits and losses resulting from using NLF airfoils on VAWT blades. These features are similar to those of Natural Laminar Flow airfoils (NLF) and gave birth to the SNLA airfoil series. Objectives formulated for the blade profile were: modest values of maximum lift coefficient, low drag at low angle of attack, high drag at high angle of attack, sharp stall, and low thickness-to-chord more » ratio. As these blades were designed for aviation applications, Sandia National Laboratories developed a family of airfoils specifically designed for VAWTs in order to decrease the Cost of Energy (COE) of the VAWT (Berg, 1990). Most VAWTs currently operating worldwide use blades of symmetrical NACA airfoil series. The successful design of an efficient Vertical Axis Wind Turbine (VAWT) can be obtained only when appropriate airfoil sections have been selected.
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