Abstract: Using the CBS (Characteristic-Based Split) finite element method, this paper studies in detail the nonlinear dynamics of stall of airfoil NACA0012.First, the Instantaneous streamline patterns and the angle of attack lift coefficient curves of flows around the static airfoil are presented, and much attention is paid to the hysteresis and jumping phenomena in the angle of attack lift coefficient curve.Next, on the basis of the fixed point bifurcation theory in the map, by introducing a map into the flow field numerical simulation the static stall is proved numerically to be a kind of saddle-node bifurcation which involves the hysteresis and jumping phenomena. Additionally the dynamic stall of the airfoil is investigated by the ALE (Arbitrary Lagrangian-Euler) method, since the saddle-node bifurcation is sensitive to external excitation, which is the pitching-motion of the airfoil around the stall attack angle.The numerical results show that the specific external excitation could significantly enhance the lift coefficient and effectively delay the stall, and it may be considered a powerful control strategy of stall.

Key words: airfoil, stall, bifurcation, nonlinear analysis, vortex shedding