Blade aerodynamic model for thick airfoils of the series NACA00xx in pre-stall conditions

Abstract

Blade aerodynamic modeling is needed for design, control, and aeroelastic studies of wind turbines. The ultimate aim of this study is to establish a blade aerodynamic model with well-quantified accuracy for thick airfoils, predominant in wind turbine blades. The study is limited to pre-stall conditions, involving only attached and trailing-edge separated flows. The account of dynamic stall will be considered in further studies. The analysis of the Glasgow University database on the family of symmetrical airfoils NACA 00xx (xx = 12,…,30) has been made by considering particularly the 2D spatiotemporal contours of the surface pressure coefficients on the suction side. Such contours provide a clear visualization of flow regime type (attached, separated or stalled) and, therefore, allow the selection of oscillatory test cases in attached or trailing-edge separated flows. The aerodynamic model of the normal force coefficient is established by improving the Beddoes–Leishman BL model. An important modification is carried on the calculation of the delayed angle of attack using the Goman–Khrabrov model, instead of the complex original procedure. There is a new aerodynamic component for simulating the trailing-edge separation. The present model, although limited to pre-stall conditions, involves ten parameters for the unsteady aerodynamic behavior. They can be obtained with the global optimization of the deviations between experimental results and model predictions. Previous optimization studies of the parameters of the BL model involve all flow regimes for test cases and do not lead to conclusive results. The parameter values obtained in the present study show a coherent and physics-expected variation with airfoil thickness that is not negligible.