CFD Analysis of Oscillating Blades for Small Horizontal Axis Wind Turbines in Dynamic Stall condition

Unsteady aerodynamics and specifically the dynamic stall phenomenon significantly affect the aerodynamic performance of the wind turbine blades. This paper presents a 2D computational investigation on the aerodynamic characteristics of three specific airfoils for small horizontal axis wind turbines subjected to unsteady viscous flow. The unsteady incompressible Navier-Stokes equations are considered, and ANSYS-Fluent CFD code is used for the flow simulation. The simulation method is validated by calculating the aerodynamic coefficients of a pitching NACA23012 airfoil and comparing the results with the corresponding published experimental data. A complete set of dynamic simulations is then performed to find lift and drag forces acting on the airfoils in different unsteady conditions such as various Reynolds numbers and different amplitude and frequency of pitching oscillations. The results of this study emphasize that the curvature of leading edge and the thickness of the airfoil have major roles in early flow separation and dynamic stall of a pitching airfoil. The dynamic stall has wide negative effects on the performance of the blades such as lift reduction, drag increment and delay in the flow reattachment that are discussed in this paper.