Supplementary material from "Tandem-wing interactions on aerodynamic performance inspired by dragonfly hovering"

Dragonflies possess two pairs of wings and the interactions between forewing (FW) and hindwing (HW) play an important role in the dragonfly flight. The effects of tandem-wing interactions on the aerodynamic performance of dragonfly hovering have been investigated. Numerical simulations of single-wing hovering without interactions and tandem-wing hovering with interactions are conducted and compared. It is found that the tandem-wing 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, tandem-wing 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.