Aerodynamic and aeroacoustic characteristics of a bionic morphing flap

Abstract

Birds adapt to the changing flight conditions by performing intricate feather-movements to manipulate the airflow. The avian wings often undergo seamless transformations at the trailing-edge to achieve camber-reflexes for extended flight envelope. A novel bionic flap is introduced on a blade section having S809 airfoil profile, inspired by the avian wings. It produces non-linear smooth wave-like deformations at the trailing-edge to enact spanwise morphing. The aerodynamic enhancement is evaluated by comparing the performance of morphing- and conventional- flap-integrated blades, over a range of angles of attack: 0°−8°, and flap deflections: 5°−10°. Comprehensive investigations are conducted at the chord-based Reynolds number (Rec) of 0.5 million to analyze the evolution of- pressure and velocity fields, surface flow, skin friction, and velocity fluctuations. The analyses reveal significant influence of variable blade-camber on the aerodynamics, particularly at the moderate angles of attack. The morphing flaps exhibit relatively superior performance in delaying flow-separation, and suppressing Reynolds stress, at all the test conditions. However, aeroacoustic analysis reveals that morphing flaps produce relatively higher broadband noise compared to conventional flaps. Overall, this research establishes supremacy of the proposed spanwise morphing over the conventional hinge-based designs in terms of tailoring and/or achieving optimal aerodynamic performance.

Keywords

• S809 airfoil
• Morphing flap
• Reynolds stress
• Skin friction
• Flow separation
• Far-field noise