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Abstract
Dragonflies possess two pairs of wings and the interactions between forewing (FW) and hindwing (HW) play an important role in dragonfly flight. The effects of tandem-wing (TW) interactions on the aerodynamic performance of dragonfly hovering have been investigated. Numerical simulations of single-wing hovering without interactions and TW hovering with interactions are conducted and compared. It is found that the TW interactions reduce the lift coefficient of FW and HW by 7.36% and 20.25% and also decrease the aerodynamic power and efficiency. The above effects are mainly caused by the interaction between the vortex structures of the FW and the HW, which makes the pressure of the wing surface and the flow field near the wings change. During the observations of dragonfly flight, it is found that the phase difference (γ) is not fixed. To explore the influence of phase difference on aerodynamic performance, TW hovering with different phase differences is studied. The results show that at γ = 22.5°, dragonflies produce the maximum lift which is more than 20% of the body weight with high efficiency; at γ = 180°, dragonflies generate the same lift as the body weight.
Highlights
Most flying insects possess only one pair of wings (e.g. Diptera and Strepsiptera), or have their forewings (FWs) and hindwings (HWs) in contact (e.g. Hymenoptera and Lepidoptera) which cannot move independently [1]
Numerical simulation is carried out for TW hovering with γ = 180° and the hover of single wing with the same kinematics
Through the comparison of aerodynamic parameters and flow fields, it is shown that when γ = 180°, the interactions between tandem forewing (TF) and tandem hindwing (TH) make the lift force and efficiency less than that of the single-wing hovering
Summary
Most flying insects possess only one pair of wings (e.g. Diptera and Strepsiptera), or have their forewings (FWs) and hindwings (HWs) in contact (e.g. Hymenoptera and Lepidoptera) which cannot move independently [1]. Insects that can control the kinematics of their four wings independently with direct musculature at each 2 wing base to deal with complex flight conditions. They can hover [1], cruise up to 54 km h−1 [2], turn 90°–180° in two or three wing beats [3,4], fly sideways, fly backwards [5] and glide [6]. Interactions between FW and HW have an important effect on aerodynamic performance of dragonflies. Adjusting phase difference in a TW flapping might be an outstanding method to control flight performance
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