Investigation of Corrugated Wing in Unsteady Motion

Abstract

Delayed stall is the most dominant lift enhancing factor in insect flapping motion. Micro air vehicle operates at Reynolds number 10 4 -10 5 ; slightly higher than the insects' Reynolds number (Re). In the present research, thefocus is to investigate "stall-absent" phenomenon at Re representative of the micro air vehicles, the effect of spanwiseflow on the leading edge vortex and also to study the effect of geometry variations on the aerodynamic performance of the wing in unsteady motion. Corrugated dragonfly airfoil with rectangular wing planform is used, however, with wing kinematics restricted to azimuth rotation only. Three-dimensionalfinitevolume method is used, through commercial software Fluent, to numerically solve time-dependent incompressible Navier-Stokes equations. Computed results at Re 34000 and 100,000 reveal the same phenomenon of delayed stall, as observed in the case of insects. Furthermore, the performance of flat plate, profiled and corrugated wing in a sweeping motion at a high angle of attack is also compared.

Three-dimensional wing structure attenuates aerodynamic efficiency in flapping fly wings

“…Noteworthy, in this study, we did not model wing stiffness and elasticity, which is in line with numerous previous studies on the significance of corrugation in dragonfly [21][22][24][25][30][31][32][33][34], bumblebee [15,35], locust [36] and fruit fly wings [6]. These studies used rigid wings and ignored any elastic deformation during wing flapping while focusing on the aerodynamic effects of surface structure.…”

“…Vortices and even stagnant air cushions may thus alter a wing's effective geometry. Trapped vortices were experimentally found in wings moving at relatively high Reynolds number [52][53], including an aerodynamic study that showed vortex trapping at Reynolds numbers between 34 000 and 100 000 but not at 3500 [33]. The latter value is at the upper end of Reynolds numbers typical for flying insects.…”

“…Although wing length-normalized mean membrane thickness in flies is only approximately 0.01% [1,12,[37][38][39][40][41], several previously published studies used an approximately 110-fold larger value (approx. 1.1%) for the mean membrane thickness [6,[31][32][33]35,42]. Our CFD simulation required a minimum wing thickness of approximately 1.17% wing length that corresponds to a thickness of 28, 75 and 114 µm in Drosophila, Musca and Calliphora, respectively (electronic supplementary material, table S1).…”

Wing Design in Flies: Properties and Aerodynamic Function

“…The majority of previously published studies used numerical or physical wing models at various Reynolds numbers for analysis and reported that wing corrugation either improves aerodynamic performance [ 56 , 58 , 65 , 66 , 118 , 135 , 136 , 137 ] or attenuates performance [ 56 , 59 , 65 , 66 , 134 , 137 , 138 , 139 ]. Other studies that reported little or no effect of corrugation on wing performance in beetles [ 55 ], dragonflies [ 140 ], bumblebees [ 141 ], hoverflies [ 142 ], and fruit flies [ 50 ] at Reynolds numbers between 35 and 34,000. Some studies, moreover, also reported inconsistent results on the significance of wing corrugation in dragonflies [ 63 , 64 , 143 , 144 ], bumblebees [ 54 ], and a generic model [ 59 ].…”

“…There is little difference in flow patterns between flat and three-dimensional fly wings but vortices and stagnant air cushions that are trapped in corrugation valleys of a wing may potentially improve lift production by changes in wing’s effective geometry [ 61 , 135 ]. Evidence for trapped vortices were experimentally found in wings moving at relatively high Reynolds number [ 63 , 64 ], including an aerodynamic study that demonstrated vortex trapping at the wing’s acceleration phase and at Reynolds numbers ranging from 34,000 to 10 5 , but not at 3500 [ 140 ]. The latter value is at the upper end of Reynolds numbers typical for flying insects.…”