Flow separation and control on a 35% thick wind turbine airfoil: experiments, simulations and data driven analysis

Modern wind turbine blades increasingly employ very thick airfoil profiles, particularly near the blade root, due to structural, manufacturing and transport constraints. These profiles are prone to flow separation, which leads to reduced performance and unstable aerodynamic loading. This type of flow is commonly controlled by passive Vortex Generators (VGs). The three-dimensional (3D) and unstable character of the flow, with or without VGs, makes it challenging to model physically or computationally and has not been sufficiently studied. This work highlights the intricacies of the 3D separated flow over very thick wind turbine airfoils and illustrates the need for rigorous analysis tailored to engineering applications. We investigate the flow over a 35% thick airfoil (DU00-W2-350), with and without flow separation control, using wind tunnel experiments, Reynolds-Averaged Navier–Stokes simulations and data driven analysis methods. We analyse force symmetry and correlations, pressure distributions, and flow instability metrics, employing Hidden Markov Models to identify and quantify unstable flow regimes. The results demonstrate that the unstable and asymmetric loading on the airfoil is effectively suppressed by the presence of VGs on both sides of the airfoil. Numerical results show strong agreement with experimental data when full-span 3D CFD models are used, while lower-cost 3D-slice models are shown to accurately capture performance trends. The paper suggests that when airfoils experience 3D separation advanced metrics should be considered instead of the commonly used time averaged values. Further, it is shown that affordable, limited-width computational modelling is sufficient in terms of flow control efficiency prediction.