Perpendicular blade–vortex-interaction over an oscillating airfoil in light dynamic stall

An experimental and numerical study was performed to investigate the effects of perpendicular blade vortex interactions on the aerodynamic performance of an oscillating airfoil. The selected test cases studied the aerodynamic interaction of a stream-wise vortex impacting on a NACA 23012 airfoil oscillating in light dynamic stall regime, representing a typical condition of the retreating blade of a helicopter in forward flight. The analysis of particle image velocimetry surveys and time-accurate simulation results enabled to point out the different effects due to the blade pitching motion on the interacting flow field. Thus, numerical results enabled to achieve a detailed insight about the aerodynamic loads acting on the oscillating airfoil in the interacting cases. In particular, the comparison with the clean airfoil case shows that a severe loss of performance is produced by the interaction of the vortex during the airfoil downstroke motion, as the vortex impact triggers the local stall of the blade section.