The wing−wing interaction mechanism of bristled wing pair in fling motion

Smallest flying insects commonly have bristled wings and use novel aerodynamic mechanisms to provide flight forces, such as the fling mechanism. In the fling motion, the left and right wings are initially parallel to each other, and then the wings rotate around the trailing edge and “open” to form a V shape. Previous studies lacked the detailed flow around bristles, so the interaction mechanism of the two bristled wings in the fling motion was not well understood. In the present study, we obtained the detailed flow around each bristle numerically and revealed the interaction mechanism of two bristled wings. The results are as follows. During the fling, the vertical force of the bristled wings is similar to that of the corresponding flat-plate wings, but the drag of the bristled wings is much smaller. When the initial distance between wings is small, the opening drag of the bristled wings can be one order of magnitude smaller than that of the flat-plate wings. This is due to the different wing–wing interaction mechanisms of the two types of wings: for the flat-plate wings, during the fling motion, a “cavity” is created between the wings, producing a very large drag on the wings; for the bristled wings, there are gaps between the bristles and Stokes flows move through the gaps; thus, the cavity effect is much weaker. Very low “opening” drag may be one of the advantages of using bristled wings for the smallest insects.