Planform Effects for Low-Reynolds-Number Thin Wings with Positive and Reflex Cambers

Abstract

To understand the planform effects on low-Reynolds-number aerodynamic characteristics for micro air vehicles, various cambered thin plate wings were studied by numerical simulations based on Reynolds-averaged Navier-Stokes solutions with transition modeling. Six wing planforms, with the same wing aspect ratio and area, a positive camber at the quarter chord location, and a reflex camber near the trailing edge for longitudinal stability were selected for the study. They include a rectangular wing, four taped wings with the same taper ratio but different leading-edge sweeps, a Zimmerman wing, and an inverse-Zimmerman wing. For validation with available windtunnel experimental data, an investigation of a circular wing planform with a similarly cambered profile is also presented. The results show that the Zimmerman wing planform gives the best lift-to-drag ratio at the design condition, whereas the tapered wing with higher leading-edge sweep produces higher maximum lift. Flow separation and vortical flow structures on the upper wing surface are presented to gain insight into the different aerodynamic characteristics for the different planforms.

Combined effects of body posture and three-dimensional wing shape enable efficient gliding in flying lizards

“…Song et al (2008) showed that for a rectangular latex wing membrane of 1.4 AR, camber resulted in a significant enhancement in lift at low AoA compared to rigid wings and exhibited a soft stall at AoA of over 40° 19 (and see 36 ). Similar benefits at low and especially high AoA regime have also been reported in studies of cambered Zimmerman airfoils 22 , 34 and cambered rectangular plates at comparable Re 35 , 37 . Altogether, these inferences supported our hypothesis of higher airfoil camber leading to increased C L and C D during the glide.…”

“…These flow structures can contribute to the overall lift production and energize the flow on the upper airfoil surface to keep the flow attached with increasing AoA, delaying stall 12 , 19 . Moreover, the delay in flow separation at high AoA could be facilitated by the placement of the lizard forelimbs at the leading edge of the patagium 21 , potentially acting as a leading edge slot and/or changing the leading-edge sweep angle 22 , 38 , although both these mechanisms remain untested.…”

“…Second, as a consequence of the lizard’s compliant airfoil along with previous observations of in-flight camber in mammalian gliders and Draco gliding lizards 2 , 3 , 18 , 20 , 21 , we hypothesized that Draco gliding lizards should also vary camber during the glide, affecting their aerodynamic force production. A higher airfoil camber would lead to greater C L and C D as seen in compliant wing models 19 , 22 . Finally, since the primary Draco wing is formed by the activation of the intercostal musculature to rotate the ribs and stretch open the patagial membrane laterally, it restricts wing movement outside the dorsal plane of the body 23 , 24 .…”