Two-Dimensional Aerodynamic Analysis of Flight in the Smallest Insects

Two-dimensional immersed boundary simulations were performed to determine how stroke plane angle and wing flexibility affect aerodynamic efficiency and energetic pseudo-efficiency for the smallest flying insects. Experimental data pertaining to small insect flight is limited and therefore, their flight mechanisms are still largely unknown. The immersed boundary method was used to solve the fully-coupled fluid-structure interaction problem of a flexible wing immersed in a two-dimensional viscous fluid. We considered five different strokes: a horizontal stroke, three hybrid strokes, and a vertical stroke. We also considered five different wing flexibilities ranging from rigid to highly flexible. Aerodynamic efficiency was defined as the ratio of the average vertical force coefficient to the average total force coefficient and energy pseudo-efficiency was defined as the ratio of the average vertical force generated by a wing to the average power delivered by the wing to the surrounding fluid. Our results indicate that at Reynolds numbers relevant to small insect flight, aerodynamic efficiency and energy efficiency decrease with increasing stroke plane angle regardless of wing flexibility and a rigid wing is aerodynamically and energetically more efficient than flexible wings.