Time-Delayed Active Control of Stall Flutter for an Airfoil via Camber Morphing

Abstract

This paper investigates a time-delayed active control for suppressing the stall flutter via camber morphing. A time-domain fluid–structure–control coupled solver is presented. This solver composes a computational fluid dynamics (CFD)-based flow solver with dynamic mesh techniques, a one- degree-of-freedom structural solver for a pitching airfoil, and a time-delayed proportional–differential controller that actuates the nonlinear camber morphing of the airfoil. The modules of the structural solver and the controller are both implanted into the CFD-based flow solver OpenFOAM. The proposed solver is first validated with the aerodynamic stall and stall-flutter experimental results, and then it is used for investigating the stall-flutter suppression performance in the time domain with nonlinear camber morphing. The numerical results with various time delays in the active control suggest that the time delay significantly impacts the response suppression effect of the stall flutter. The closed-loop controls with time delays ranging from 0.01 to 0.15 s can suppress stall flutter. The suppression effect reaches the best when as it reduces the amplitude of the limit-cycle response by 60%. The active control mechanism of the time-delayed camber morphing is analyzed in terms of the flow pattern and energy transfer in depth.