Investigation into Reynolds number effects on a biomimetic flapping wing

Abstract

This research investigated the behavior of a Manduca sexta inspired biomimetic wing as a function of Reynolds number by measuring the aerodynamic forces produced by varying the characteristic wing length and testing at air densities from atmospheric to near vacuum. A six degree of freedom balance was used to measure forces and moments, while high speed cameras were used to measure wing stroke angle. An in-house created graphical user interface was used to vary the voltage of the drive signal sent to the piezoelectric actuator which determined the wing stroke angle. The Air Force Institute of Technology baseline 50 mm wing was compared to wings manufactured with 55, 60, 65, and 70 mm spans, while maintaining a constant aspect ratio. Tests were conducted in a vacuum chamber at air densities between 0.5% and 100% of atmospheric pressure. Increasing the wingspan increased the wing’s weight, which reduced the first natural frequency; and did not result in an increase in vertical force over the baseline 50 mm wing. However, if the decrease in natural frequency corresponding to the increased wing span was counteracted by increasing the thickness of the joint material in the linkage mechanism, vertical force production increased over the baseline wing planform. Of the wings built with the more robust flapping mechanism, the 55 mm wing span produced 95% more vertical force at a 26% higher flapping frequency, while the 70 mm wing span produced 165% more vertical force at a 10% lower frequency than the Air Force Institute of Technology baseline wing. Negligible forces and moments were measured at vacuum, where the wing exhibited predominantly inertial motion, revealing flight forces measured in atmosphere are almost wholly limited to interaction with the surrounding air. Lastly, there was a rough correlation between Reynolds number and vertical force, indicating Reynolds number is a useful modelling parameter to predict lift and corresponding aerodynamic coefficients for a specific wing design.

Recent progress in flapping wings for micro aerial vehicle applications

“…Hope et al. 84 studied the effect of Reynolds number on aerodynamic performance of five wings with a span of 50, 55, 60, 65, and 70 mm. They found that vertical force on wing increases with wingspan, for example, 70 mm wingspan produced 165% more vertical force with a 10% lower frequency than baseline wing of 50 mm.…”

A Numerical Study about the Flight of the Dragonfly: 2D gliding and 3D hovering regimes

“…It consists of a vortex with an appreciable spanwise flow maintained at the leading edge of the wing during the upstroke and downstroke. At pronation and supination, the vortex is shed, after which a new vortex is quickly formed [6]. Several studies have shown that the wing benefits from the attachment of the LEV because of the low-pressure core of the LEV acting on the wing.…”

“…In such particular environment, force generation mechanisms are based on vortex detachment: Amiralaei et al [2] and Yao et al [3] provided a general overview about all the vortices involved into low-Reynolds flight dynamics. The majority of the articles focus on the leading edge vortex (LEV), recognized as the principal actor in this scenario [4], [5], [6], [7], [8], [9]. Moreover, what emerges from the definition of MAV, is that is mandatory to reduce as much as possible both the payload and the space occupied by mechanical components.…”

A numerical study about the flight of the dragonfly: 2D gliding and 3D hovering regimes

“…It consists of a vortex with appreciable spanwise flow maintained at the leading edge of the wing during the upstroke and downstroke. At pronation and supination, the vortex is shed, after which a new vortex is quickly formed [21]. Several studies have shown that the wing benefits from the attachment of the LEV because of the low-pressure core of the LEV acting on the wing.…”