Comparative Flapping Aerodynamics of Smooth and Tubercle Wings in Forward Flight

ABSTRACT

In this talk, the near-wake flow dynamics and their influence on the aerodynamic thrust characteristics of high-aspect-ratio flapping wings with leading-edge tubercles, compared to a smooth leading-edge (baseline) counterpart, under forward flight conditions, will be discussed. Using numerical simulations validated with in-house water tunnel experiments, the aerodynamic performance is analysed across a range of non-dimensional flapping frequencies. The wing with sinusoidal tubercle geometry consistently underperforms the baseline wing in both time-averaged and transient thrust generation. This disparity arises from distinct wake dynamics. While the baseline wing sustains thrust through the formation of coherent leading-edge vortices, the tubercle wing generates counter-rotating vortex pairs (CRVPs) that lift away from the surface. The CRVP liftoff leads to the formation of secondary structures, including residual CRVPs and hairpin vortices, which impede thrust recovery. Moreover, the residual CRVPs form complex loops that interact with the wing surface, creating an unfavourable flow environment that exacerbates thrust loss. At higher flapping frequencies, these interactions intensify, revealing loop-like vortex formations along the wingspan, further reducing pressure differentials essential for thrust generation.