Numerical investigation of the aerodynamic benefits of wing-wing interactions in a dragonfly-like flapping wing

Numerical simulations are performed to investigate the aerodynamic benefits of wing-wing interactions on a dragonfly-like flapping wing while hovering, at a value of Reynolds number Re set to 630. The local phase shift ψ and wing spacing L* (L/c) are varied to observe their influence on aerodynamic performance. The results show that the aerodynamic benefits due to interactions are strongly dependent on both ψ and L*. The wing-wing interactions are beneficial for the in-phase stroking pattern at ψ = 0° when 1.2 ≤ L* ≤ 2.3, while it is extremely detrimental for the counter stroking pattern at ψ = 180° when 1.2 ≤ L* ≤ 2.3; these benefits and drawbacks are dependent on the timing of the interactions. The best case, when ψ = 0° and L* = 2.1, can increase the time-averaged vertical force coefficient C_v¯ up to ∼10 % in comparison to the without-interaction case. Two unsteady flow features namely the “enhanced dipole structure” and the “in-sync of wake capture and wing-wing interactions” are observed that increase the vertical force generation in hovering dragonflies. The overall downward momentum imparted by the wing is larger for ψ = 0° in comparison to ψ = 180° as the wake has high vertical velocities due to the constructive role played by wing-wing interactions.