Aerodynamic effect of stroke amplitude on hovering performance of a three-dimensional tandem flapping wing.

In the present numerical investigation we studied the effect of forewing and hindwing stroke amplitude (ϕo) on the aerodynamic performance of dragonfly (or damselfly) hovering flight. Three-dimensional numerical simulation was performed for two wings with a tandem arrangement flapping along an inclined stroke plane. Simulations were conducted for identical as well as non-identical stroke amplitudes of both wings, oscillating with three phase differences:γ= 0∘, 90∘and180∘. For identical stroke amplitudes, the higher stroke amplitude reduces the vertical force coefficients of both wings. Forγ= 0∘, forewing lift is significantly enhanced for higher stroke amplitudes due to leading edge vortex interaction. Forγ= 90∘and180∘, the wing-wing interaction is found to be detrimental to the vertical force coefficient of both wings. The presence of the forewing reduces hindwing lift for allγ, with maximum lift reduction observed forγ= 180∘. The maximum hovering efficiency for identical stroke amplitudes is obtained forϕo= 50∘whenγ= 0∘. For non-identical stroke amplitudes, the hindwing lift reduces with an increase in forewing stroke amplitude for allγ. Also, forewing lift increases with hindwing stroke amplitude whenγ= 0∘. However, forγ= 90∘and180∘, forewing lift is reduced for higher hindwing stroke amplitudes. It was found that non-identical stroke amplitudes are detrimental to the hovering efficiency of dragonfly flight. The present study will help us optimize wing kinematics during the development of dragonfly-inspired micro air vehicles.