Wing-wake interaction: comparison of 2D and 3D flapping wings in hover flight

Area of Science:

• Fluid Dynamics
• Aerodynamics
• Bio-inspired Engineering

Background:

• Wing-wake interaction is crucial for hovering flight.
• Understanding the differences between 2D and 3D flapping wing aerodynamics is essential for bio-inspired designs.

Purpose of the Study:

• To investigate the impact of three-dimensionality on wing-wake interaction mechanisms in hovering flapping wings.
• To compare the aerodynamic performance and lift generation of 2D, quasi-3D, and 3D flapping wing configurations.

Main Methods:

• Numerical simulations were performed at a Reynolds number of 100.
• Flapping wing configurations were systematically varied from 2D to 3D using aspect ratio and Rossby number.
• Four primary aerodynamic mechanisms influencing wing-wake interaction were analyzed: induced jet, downwash/upwash, leading-edge vortex (LEV) shedding, and closely attached LEV formation.

Main Results:

• Three-dimensionality diminishes the role of LEV shedding due to previous stroke interactions and enhances the formation of a closely attached LEV, which boosts lift.
• The dual-peak lift coefficient pattern of 2D wings transforms into a single-peak pattern for 3D wings.
• Mean lift enhancement from wing-wake interaction decreases rapidly with increasing three-dimensionality.

Conclusions:

• Three-dimensionality significantly alters the dominant aerodynamic mechanisms in flapping wing flight.
• For parameters similar to natural flyers, wing-wake interaction provides minimal lift enhancement and a slight increase in energy cost.
• The study highlights the importance of considering three-dimensional effects in the design of flapping wing systems.