Numerical Investigation of Three-Dimensional Effects on Deep Dynamic Stall Experiments

Computational Fluid Dynamics simulations were carried out in two and three spatial dimensions to assess the suitability of numerical models for the simulation of deep dynamic stall experiments. The numerical results were compared to pressure measurements and Particle Image Velocimetry flow surveys carried out on a pitching NACA 23012 airfoil. The pitching cycles considered as test cases reproduce the deep dynamic stall condition for a helicopter rotor retreating blade section. The comparison of the airloads curves and of the pressure distribution over the airfoil surface shows that a three-dimensional numerical model can better reproduce the experimental airloads behaviour during the pitching cycles. The three-dimensional simulation results show also a better reproduction of the vortical structures observed by PIV. The solution of the simulation obtained over a three-dimensional grid independent from the wind tunnel geometry highlighted the relevance of three-dimensional effects on the flow field that are mainly due to the intrinsic three-dimensional nature of dynamic stall.