Physics of Dynamic Stall Vortex During Pitching Oscillation of Dynamic Airfoil

Dynamic stall, which has a significant effect on the aerodynamic performances of dynamic airfoils, is closely related to the physics of the dynamic stall vortex (DSV). The physics of the DSV on the NACA 0012 airfoil was experimentally studied using unsteady pressure measurements with high time accuracy. The experimental Reynolds number was Re = 1.5 × 106, and the reduced frequency was k = 0.069. The propagation of the unsteady pressure field during the dynamic stall process was analyzed in detail. The motion characteristics of the DSV were examined, including its near-wall development characteristics and near-wall evolution velocity. Moreover, the frequency characteristics of the near-wall DSV were studied using wavelet analysis combined with proper orthogonal decomposition (POD) technology. In addition, the effects of the mean angle of attack (AoA) and the amplitude on the DSV motion and frequency characteristics were examined in detail. The effects of the mean AoA on the near-wall DSV strength and the propagation velocity were linear, while the effects of amplitude were nonlinear. The mean AoA and amplitude had a significant influence on the frequency of the leading-edge vortex (LEV) at the initial stage of the DSV development (x/c = 0.10–0.20). This work allows the DSV physics to be understood more deeply. Graphic abstract