Aerodynamic interference of three flapping wings in tandem configuration

Collective movements are common in nature, such as the swimming of fish schools and the flight of birds in formation. The aero/hydrodynamic performance of such movements is a research hotspot at present. As a continuation of the previous research [X. G. Meng et al., "Aerodynamic performance and flow mechanism of multi-flapping wings with different spatial arrangements," Phys. Fluids 34, 021907 (2022)], this study examined the aerodynamic interference effect of three tandem flapping wings at different morphological and kinematic parameters. Computational fluid dynamics was used with the aspect ratio (AR) of the wing ranging from 2.75 to 4.75, stroke amplitude (f) from 60? to 120?, advance ratio (J) from 0.25 to 0.6, and Reynolds number (Re) from 200 to 2000. The aerodynamic interference for the tandem flapping wings includes three effects, namely, the narrow channel effect, the downwash effect, and the wake capture effect. The AR, f, and J can significantly influence the evolution of the vortex structures of the three-flapping-wing system, especially the velocity of wake vortices developing downstream. As a result, the downwash effect in the downstroke and the wake capture effect in the upstroke change obviously with these parameters. Due to the decreasing viscous effect with the increase in Re, the wake capture effect, which can improve the thrust of the wings, is more obvious at higher Re. This study further deepens our insight into the flow physics of the multi-flapping wings and provides a theoretical basis for improving the aerodynamic performance of multi-flapping-wing vehicles in the future.