Flow Structure and Force Generation on Flapping Wings at Low Reynolds Numbers Relevant to the Flight of Tiny Insects

Abstract

In contrast to larger species, little is known about the flight of the smallest flying insects, such as thrips and fairyflies. These tiny animals range from 300 to 1000 microns in length and fly at Reynolds numbers ranging from about 4 to 60. Previous work with numerical and physical models have shown that the aerodynamics of these diminutive insects is significantly different from that of larger animals, but most of these studies have relied on two-dimensional approximations. There can, however, be significant differences between two-and three-dimensional flows, as has been found for larger insects. To better understand the flight of the smallest insects, we have performed a systematic study of the forces and flow structures around a three-dimensional revolving elliptical wing. We used both a dynamically scaled physical model and a three-dimensional computational model at Reynolds numbers ranging from 1 to 130 and angles of attacks ranging from 0 • to 90 •. The results of the physical and computational models were in good agreement and showed that dimensionless drag, aerodynamic efficiency, and spanwise flow all decrease with decreasing Reynolds number. In addition, both the leading and trailing edge vortices remain attached to the wing over the scales relevant to the smallest flying insects. Overall, these observations suggest that there are drastic differences in the aerodynamics of flight at the scale of the smallest flying animals.

Neuromechanical wave resonance in jellyfish swimming

“…Numerical simulations were performed using a fully coupled fluid-structure interaction (FSI) model of an elastic bell body in a viscous fluid. To simulate this problem, we used a hybrid immersed boundary/finite element framework (40)(41)(42) that has been applied to a variety of biological FSI problems (43)(44)(45)(46). The hemiellipsoid jellyfish bell model that is used in this study was previously validated in forward-swimming studies (32,47).…”

Collective locomotion of two-dimensional lattices of flapping plates. Part 2. Lattice flows and propulsive efficiency

“…We have studied propulsive properties of flapping lattices of plates at Re = 10-70, where the flows often become time periodic within 5-30 flapping periods. This Re range is typical for submillimetre-to centimetre-scale flying and swimming organisms (Childress & Dudley 2004;Miller & Peskin 2004, 2009Jones et al 2015;Santhanakrishnan et al 2018;Skipper, Murphy & Webster 2019), and is relevant to the increasing number of robotic flying and swimming vehicles that inhabit this size range (Chen et al 2017;Hu et al 2018;Zhang & Diller 2018;Chen et al 2019;Ren et al 2019). Froude efficiency is typically much lower in this Re range than in the higher Re range typical of most fish and birds (Shyy, Berg & Ljungqvist 1999;Triantafyllou, Triantafyllou & Yue 2000;Fish & Lauder 2006), so collective locomotion may be relatively more important for achieving locomotion (efficiently, or at all, at very low Re where it is no longer possible for an isolated flapping body).…”

“…2015; Santhanakrishnan et al. 2018; Skipper, Murphy & Webster 2019), and is relevant to the increasing number of robotic flying and swimming vehicles that inhabit this size range (Chen et al. 2017; Hu et al.…”

Pausing after clap reduces power required to fling wings apart at low Reynolds number

“…The attached LEV delays stall and helps in lift generation (Dickinson et al 1999, Ellington 1999. In contrast, both the LEV and TEV do not separate from a wing during linear translation (Miller & Peskin 2004) and revolution for Re c ≤ 32 (Santhanakrishnan et al 2018). This LEV-TEV 'vortical symmetry' has been proposed to decrease lift in tiny insect flight (Miller & Peskin 2004), due to reduction in the time rate of change of the first moment of vorticity (Wu 1981).…”