Numerical and Experimental Study of a Covert-Inspired Passively Deployable Flap for Aerodynamic Lift Enhancement

Bio-inspired flow control techniques have the potential to overcome the operational and environmental limitations of traditional flow control techniques. One of those bio-inspired flow control techniques is covert-inspired flaps. Covert bird feathers act as aeroelastic high-lift devices capable of controlling separation and mitigating stall. This study investigates the performance characteristics of a covert-inspired passive flow control technique using numerical simulations and experiments at two significantly different Reynolds numbers (Re), Re = 1000 and Re = 2 × 10⁵, respectively. The covert feathers are modeled as passively deployable, torsionally hinged flaps on the upper surface of a NACA2414 airfoil. We perform a systematic parametric study, where we varied the flap hinge location, hinge stiffness, and rotational inertia of the flap. Results from this study quantify the effects of the hinge stiffness and flap inertia on lift improvements and flap dynamics across Reynolds number. A key feature of this study is the assessment of critical similarities and differences in the physics of the covert-inspired flap FSI system across these different Reynolds numbers. We perform this comparison by measuring and contrasting the flow and flap dynamics as well as the average and instantaneous lift force.