Clap and Fling in Tiny Insect Flight: Role of the Porous Flow Introduced by Bristled Wings

Abstract

In contrast to the flapping flight of insects of length scales ranging from the fruit fly to the hawk moth, the aerodynamics of flight in insects such as thrips that are 1 mm or less in length is not as well understood. These smallest insects typically fly at Reynolds numbers (Re) of 10 or lower and are of ecological and agricultural importance. Flight aerodynamics change at Re in the range of 5−10 due to increased viscous forces, and the ratio of lift to drag forces decreases significantly. Nevertheless, these insects are capable of traveling long distances. A detailed study of the relevant aerodynamics is thus necessary to connect their locomotion to the observed ecological behavior and dispersal mechanics. These tiny insects have been proposed to augment lift through adaptations in flight kinematics, wing flexibility and wing morphology. With reference to flight kinematics, thrips and other tiny insects clap their wings at the end of each upstroke and fling them apart at the beginning of each downstroke. These insects also have highly bristled wing surfaces as opposed to solid wings. We explore the role of bristled wings by modeling them as porous structures. 2D numerical fluid−structure interaction simulations are then used to quantify aerodynamic forces generated during porous−wing clap and fling. The input parameters for the simulations are obtained from high−speed video recordings of actual insects. An idealized form of the clap and fling motion of two wings immersed in fluid is then considered. The effect of having bristles on the flow field is examined and compared to that of an equivalent solid wing.

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