Wing-wake interaction of three-dimensional flapping wings

Experimental and numerical studies were conducted to investigate the effects of acceleration and deceleration durations on the wake capture effects on three-dimensional fruit-fly-inspired flapping wings. The contribution from the wake capture to lift and drag coefficients was isolated by comparing the forces generated by a wing in a quiescent fluid where the wake capture effect was absent, with the forces generated in a periodic flowfield where the full wake capture effect was encountered. The results showed that wake capture caused lift and drag coefficients to increase noticeably at the start of each flapping stroke. Also, a reduction in deceleration duration enhanced the wake capture effect, and a reduction in acceleration duration caused an earlier onset of wake capture with no significant effect on the force magnitudes contributed by the wake capture. Moreover, the effect of reducing the acceleration and deceleration durations in the same flapping motion resembled superposition of the two individual effects. The present study helps toward a better understanding of the fluid dynamics of the wing-wake interaction.