Three-dimensional Unsteady Aerodynamic Characteristics of Wing-body-vortex Interactions in Insects' Flapping Flight

Abstract

This paper investigates the unsteady aerodynamic features of wing-body-vortex interactions and the effects of geometric factors such as wing shape and body angle in insects' flapping motions under forward flight condition. A realistic wing trajectory, called the 'figure-of-eight' motion, is extracted from a blowfly (Phormia regina)'s tethered flight experiment under the freestream velocity of 2.75m/s. Since the flow field around the blowfly exhibits the characteristics of low-Reynolds number flow, three-dimensional unsteady incompressible Navier-Stokes equations are employed as the governing equations. In order to simulate the realistic insect flapping flight including geometric and kinematical complexity with a sufficient level of grid quality, the overset grid technique is used. From the authors' previous researches on two-and three-dimensional rigid wing simulation, it has been observed that the pattern of vortical flows and the interaction of vortices play an significant role in generating unsteady aerodynamic forces and determining the propulsive efficiency of flapping motion. Detailed numerical simulations of five types of wings are carried out under various body angles to examine unsteady flow characteristics resulting from the wing-body-vortex interactions, and the results are compared with those of the wing only case. Nomenclature c m = mean chord length U ∞ = freestream velocity U max = maximum wing velocity at aerodynamic mean chord ν = freestream kinematic viscosity Re = Reynolds number (=U max c m /ν)= flapping frequency in Hertz k = reduced frequency in terms of c m (= fc m /U max ) t = non-dimensional time T = non-dimensional flapping period χ = body angle α(t) = pitch angle motion ф(t) = position angle motion θ(t) = elevation angle motion