Numerical investigation of fluid-wing interaction during forward flapping flight under wind gust conditions with varying aspect ratios

Flapping wings, utilized for locomotion in various aerial organisms, frequently operate in turbulent environments where gust disturbances can significantly affect their aerodynamic performance. Due to the inherently unsteady nature of flapping flight, aerodynamic parameters such as forces and moments fluctuate within a bounded range. However, external disturbances may drive these parameters beyond their normal range. Depending on the flyer’s active mechanisms, such as wingbeat modulation, wing flexibility, stroke asymmetry, etc., the system may dampen the disturbance and restore aerodynamic parameters to their stable margins. While the role of interspecific variation in flight performance has been widely studied, the impact of intraspecific differences, particularly between individuals of varying size, remains poorly understood. This study focuses on the beetle Batocera rufomaculata, comparing the aerodynamic response of small and large individuals subjected to a downward step-profile gust. Notably, smaller individuals of Batocera exhibit enhanced aerodynamic performance, a trend that contrasts with general patterns observed across species, making this case particularly compelling for aerodynamic investigation.

To assess the gust response and potential flight stabilization, defined here as the ability to operate at their normal range, a three-dimensional numerical simulation is performed using the Reynolds-Averaged Navier-Stokes (RANS) approach. Two wings, representative of the small and large individuals, are modeled with corresponding aspect ratios and natural flapping kinematics, including heaving, pitching, and stroking, implemented via an overset mesh technique. Key performance metrics such as lift drop magnitude, lift recovery time, roll and pitch moments, and gust rejection ratio are evaluated and compared. The findings aim to shed light on the aerodynamic strategies underlying stability and lift control across varying wing geometries and kinematic patterns during forward flapping flight.