Numerical investigation into the effects of stroke trajectory on the aerodynamic performance of insect hovering flight

Abstract

Various stroke trajectories may be observed in insect hovering flight in nature; however their influences on the flight performance of insect are not well estimated. In this study, a numerical investigation into the effects of stroke trajectories on the aerodynamic performance of insect hovering flight is carried out through the solution of the two-dimensional unsteady incompressible Navier-Stokes equations. An insect wing model with ellipse cross section in hovering flight is considered for the purpose and four types of idealized trajectories (Named linear, oval, figure-eight and double-eight) which possess different deviation characteristics from the stroke plane are examined. The influences of the deviation amplitude of trajectory, the attack angle of wing and the inclined angle of stroke plane on the aerodynamic characteristics of hovering wing are systematically analyzed. The results show that in the case of the wing in a normal hovering flight where the stroke plane is horizontal, the trajectory deviation from the stroke plane weakens the aerodynamic performance for each trajectory case considered, and this deteriorative effect becomes more serious as the amplitude of deviation increases. With regard to the influence of the angle of attack, the results show that the time-averaged drag force and power consumption increase monotonically with the angle, whereas the time-averaged lift force and the lifting efficiency increase first and then decrease as the angle increases further. In the case of a hovering flight with an inclined stroke plane, distinctly different trends from a normal hovering flight are obtained.