Stereo PIV investigation of flapping beetle wings in forward flight

Understanding the unsteady aerodynamics of insect flight is vital for advancing bio-inspired micro aerial vehicles (MAVs). Insect flight dynamics are governed by the complex interplay between wing kinematics and the surrounding flow environment, especially in low Reynolds number regimes. To explore aerodynamic performance and wake evolution in flapping flight, we investigate the near-wake flow characteristics of the mango stem borer beetle (Batocera rufomaculata), which operates at chord-base Reynolds numbers on the order of 10³. Flow field measurements were conducted in the Trefftz plane behind a beetle hindwing undergoing symmetric flapping motion in an open-loop wind tunnel, simulating forward flight conditions. Flapping was driven by a mechanical actuation device operating at variable frequencies, enabling comparisons across wing sizes, wingbeat frequencies and wind conditions. Using stereo particle image velocimetry (StereoPIV), we captured three-component velocity fields in the near wake to study vortex evolution, momentum redistribution, and the development of spanwise coherent flow structures. Preliminary results depict distinct wake patterns and vortex dynamics that vary with wing morphology and flapping input, offering new insights into fluid-structure interactions and unsteady aerodynamic mechanisms. These findings advance the understanding of natural flapping systems and support the design of MAVs capable of navigating complex flow environments.