Meeting Abstract

84.5  Tuesday, Jan. 6  Aerodynamic Effect of Forewing-Hindwing Interactions in Hovering and Forward Flight of Dragonfly HU, Zheng; DENG, Xinyan*; University of Delaware; University of Delaware deng@udel.edu

Dragonflies move each wing independently and therefore may alter the phase differencebetween the forewing and hindwing stroke cycles. They are observed to change the phase difference for different flight modes. We investigated the aerodynamic effect of phase difference during hovering and forward flight with a 60 inclined stroke plane by using a pair of dynamically scaled robotic dragonfly model wings. Aerodynamic forces were measured while phase difference was systematically varied. The results showed that, i) for hovering flight, 0 phase difference enhanced the lift force on both forewing and hindwing; 180 was detrimental for lift generation, but was beneficial for vibration suppression and body stabilization. This result may help understand the dragonfly behavior that 0 was used in acceleration mode while 180 was used in hovering mode. ii) For forward flight, wing-wing interaction was always beneficial for forewing lift while detrimental for hindwing lift; the total lift was only slightly reduced with 0~90 phase difference and significantly decreased by 38% with 270 phase difference. This result may explain why dragonflies employ 50~100 during forward flight, while 270 is never favored. Thrust force was also reduced by wing-wing interaction to some extent. We experimentally investigated the wing-wing interaction mechanism and measured two types of interaction flow: sharp upwash and mild flow. The former was caused by the leading edge vortex (LEV) of hindwing and resulted in lift enhancement on the forewing, while the latter is a kind of local flow interaction which resulted in either an upwash or downwash.