Lift Enhancement of an airfoil using Covert-inspired Dual-side Flexible Flaps

Abstract

The remarkable advancement of MAVs (Micro Aerial Vehicles) and UAVs (Unmanned Aerial Vehicles) has received significant attention due to their importance in various engineering applications such as search and rescue, cargo transport and urban mobility. However, despite advances in technology, MAVs’ and UAVs’ flight performance remains inferior to that of avian flyers, which has led to extensive investigations of the flow-structure interaction mechanisms associated with avian flight. In particular, covert feathers, which are flexible structures attached to both the upper (suction-side) and lower (pressure-side) surfaces of a bird’s wing, are known to be passively deployed in response to aerodynamic forces for lift enhancement and stall delay. Despite their functional importance and the influence of their attachment positions, most previous studies on bio-inspired flaps have investigated the aerodynamic effects of flaps placed on either the suction-side or pressure-side, without considering their combined roles. In the present study, we perform numerical simulations of a NACA0012 airfoil equipped with dual-side flexible flaps on both the suction and pressure sides to explore the effects of the dual-side configurations on aerodynamic performance by systematically varying the flap positions (xs, xp) and bending rigidity (γ) on both the suction-side and pressure-side. The dual-side flexible flap system achieves superior lift enhancement through synergistic flow control that fundamentally reorganizes vortex dynamics across both airfoil surfaces, a coordinated mechanism unattainable by modifying either surface independently. Through comprehensive wake stability analysis considering both lift enhancement and flow stability characteristics, an optimal dual-flap configuration (xs, xp, γ)=(0.4, 0.9, 0.0005) is identified that maximizes aerodynamic performance while maintaining stable periodic vortex shedding. Keywords: Fluid structure interaction, Lift enhancement, flow control, covert feather