Post-stall Aerodynamics Research Articles

Mesh and model requirements for capturing deep-stall aerodynamics in low-Mach-number flows

The paper 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 0012 and 0021 airfoils, with specific focus on the deep-stall regime. At high angles of attack (α), wind turbine blades routinely experience vortex-induced vibrations, which can cause significant structural damages. Accurate predictions of post-stall aerodynamics can identify the frequencies at which such vibrations maybe triggered. In this context, the NACA 0012 airfoil simulations are conducted at a chord-based Reynolds number, , with the k-ω Shear-Stress Transport Reynolds-Averaged Navier-Stokes (RANS) and Improved Delayed Detached Eddy Simulation (IDDES) hybrid RANS-Large Eddy Simulation turbulence models. The effect of mesh resolution both in the wall-normal and spanwise directions is investigated. Only the IDDES model with a minimum spanwise resolution of 24 cells per chord length correctly predicts the aerodynamic forces. Spectral analysis shows the peak primary shedding frequency at , which signifies the end of the stall region. In the post-stall regime, both lift and drag frequencies drop asymptotically with increasing α. The Strouhal number, based on normalised chord length, remains nearly constant in this region. Based on this study, NACA 0021 airfoil runs are performed with IDDES for and on the finest wall-normal mesh and three spanwise grids. Simulations conducted on the finer spanwise grids demonstrate grid independence and show good agreement with experiments. The effect of varying on the airfoil frequency statistics is investigated. Additionally, comparison studies are presented to investigate the impact of airfoil thickness on the frequency content at . The results from the study provide guidance on the choice of mesh resolution with the IDDES model to accurately capture aerodynamic quantities for complex industrial applications.

Unsteady 3D Post-Stall Aerodynamics Accounting for Effective Loss in Camber Due to Flow Separation

Unsteady 3D Post-Stall Aerodynamics Accounting for Effective Loss in Camber Due to Flow Separation

Insight into wind turbine stall and post‐stall aerodynamics

AbstractThe objective of this study was to evaluate measured NASA Ames Unsteady Aerodynamic Experiment post‐stall blade element data and to provide guidelines for developing an empirical approach that predicts post‐stall aerofoil characteristics. Blade element data were analysed from the five radial stations of the baseline 5·03 m radius rotor. A lifting surface/prescribed wake performance prediction method was used to determine a reference angle of attack that corresponds to the measured blade element data. Using the measured normal and tangential force coefficients and estimated angle of attack, spanwise distributions of lift and drag performance characteristics were derived along with the circulation distributions. Guidelines for a new stall and post‐stall model based on the measured trends in the aerofoil performance characteristics, along with flat plate theory, are proposed for predicting the peak and post‐peak power. Copyright © 2004 John Wiley & Sons, Ltd.