Analysis of Airfoil Stall Control Using Dynamic Mode Decomposition

Airfoil stall is a major inhibitor of aircraft performance. Many methods have been successfully shown to inhibit or eliminate stall. However, the underlying dynamics of control remains relatively obscure because of the highly nonlinear nature of turbulence. A major challenge is the a priori estimation of actuation parameters without resorting to trial and error. Such estimation of parameters requires a physics-based understanding of the flowfield and its response to actuation. To study this, high-fidelity large-eddy simulations are employed to analyze active control by exploring the key dynamic modes, without and with control, through dynamic mode decomposition. A NACA 0015 stalled airfoil is considered at a Reynolds number of 100,000 and a 15deg angle of attack. The results suggest that the dominant mode representing stall has an effective Strouhal number of two. Simulations are then performed by modeling control at St = 2 using a nanosecond-pulsed dielectric barrier discharge near the leading edge. Introduction of control at this frequency is shown to successfully mitigate stall. Further analyses show that control tends to excite and destabilize predominantly higher frequencies, but it specifically stabilizes the low-frequency large-scale structures associated with stall. The results establish promise of the methodology in a priori estimation of control frequency.