Effects of Flexible Wings in Hover Flight at Fruit Fly Scale

Abstract

Fruit flies have flexible wings that deform significantly. To explore the fluid-structure interaction of flexible wings, we use a well-validated Navier-Stokes equation solver, fullycoupled with a structural dynamics solver. A hover flight is considered at a Reynolds number of Re = 100, equivalent to that of fruit flies. The thickness and density of the simulated wing also corresponds to a fruit fly wing. The wing stiffness and motion amplitude are varied to assess their influences on the resulting aerodynamic performance and structural response. Highest lift of 3.3 is obtained at the lowest-amplitude, highest-frequency motion (reduced frequency of 3.0) at the lowest stiffness (frequency ratio of 0.7) wing, although the corresponding power required is also high. Optimal efficiency of 0.6 was achieved for a lower reduced frequency of 0.3 and frequency ratio 0.35. Compared to the previously reported results at water tunnel scale, the aerodynamic characteristics were similar, while the structural response varied significantly. Despite these differences, the time-averaged lift scaled with the shape deformation parameter γ. The resulting flexible wing motion for the most efficient case was closely aligned to the the fruit fly measurements, suggesting that fruit fly flight aims to conserve energy, rather than to generate large forces.