Effect of butterfly-scale-inspired surface patterning on the leading edge vortex growth

Abstract

The effects of longitudinal square grooves on the growth of the leading edge vortex (LEV) produced by an impulsively-started flat plate are investigated experimentally. The Reynolds numbers are 1416, 2833 and 5667, and the maximum vortex formation time is 2.8. The square grooves are inspired by the surface patterning (scales) on butterfly wings. It is hypothesized that the grooves play a role in the LEV formation and development by creating a stronger secondary vortex near the LE that impedes the growth of the LEV. To evaluate this hypothesis, circulation curves of the total positive vorticity field and LEV of a smooth plate and grooved plate are compared. Also, the secondary vorticity generated by the LEV interaction with the patterned surface is studied, as well as the subsequent effect on the LEV’s growth rate and peak circulation. The vortex development process varies for each Reynolds number. At the lowest number, the effects of the grooves are minimal; however, they are most significant at the highest Reynolds number where the unsteady interactions between the secondary vortex and the leading edge shear layer become stronger for the grooved plate causing an earlier separation of the LEV. Therefore, contrary to the hypothesis, the data shows that stronger secondary vortex causes a stronger LEV with an earlier separation. The stronger secondary vortex interacts more rigorously with the LE shear layer causing the latter to feed more concentrated vorticity to the LEV.