Determination of the angle of attack from blade-resolved CFD, towards improved modelling of blade-vortex interaction on rotors

Details

Supervisors

Winckelmans, Grégoire

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil mécanicien, à finalité spécialisée

Abstract

This work investigates the accuracy of a method based on flow velocity for extracting the angle of attack (AoA) from CFD simulations. The post-processing approach uses the velocity, pressure and density fields extracted along iso-distance contours surrounding the airfoil to estimate the circulation and the AoA. The lift coefficient is then predicted using the Kutta–Joukowski law. Two-dimensional wall-resolved incompressible and weakly compressible simulations of a NACA0012 airfoil are first used to assess the circulation conservation and the accuracy of both the extracted AoA and the lift estimation along several extraction contours. The influence of weak compressibility effects is investigated up to Mach 0.5. Wall-resolved and wall-modeled RANS simulations are then compared to evaluate whether wall functions can accurately reproduce the near-wall flow behaviour while reducing the computational cost. Finally, the method is applied to three-dimensional configurations in which counter-rotating Lamb–Oseen vortices are imposed at the inlet to reproduce blade-vortex interaction. The results show that the circulation is not perfectly conserved between contours, even in incompressible configurations, due to a small amount of vorticity associated with numerical effects enclosed between the contours. Under weak compressibility conditions, the classical incompressible Kutta–Joukowski formulation remains a good approximation, although compressibility effects become more visible as the Mach number increases. The wall-modeled simulations remain consistent with the wall-resolved reference cases, which justifies their use in the subsequent three-dimensional simulations. In the three-dimensional simulations, the spanwise lift coefficient distribution is accurately estimated for the Ω0.25c contour. Strong spanwise variations in the estimated quantities are observed near the vortex cores, showing that the estimation is sensitive to localized vortical structures.