Three-dimensional flow and lift characteristics of a hovering ruby-throated hummingbird

Abstract

A three-dimensional computational fluid dynamics simulation is performed for a ruby-throated hummingbird (Archilochus colubris) in hovering flight. Realistic wing kinematics are adopted in the numerical model by reconstructing the wing motion from high-speed imaging data of the bird. Lift history and the three-dimensional flow pattern around the wing in full stroke cycles are captured in the simulation. Significant asymmetry is observed for lift production within a stroke cycle. In particular, the downstroke generates about 2.5 times as much vertical force as the upstroke, a result that confirms the estimate based on the measurement of the circulation in a previous experimental study. Associated with lift production is the similar power imbalance between the two half strokes. Further analysis shows that in addition to the angle of attack, wing velocity and surface area, drag-based force and wing-wake interaction also contribute significantly to the lift asymmetry. Though the wing-wake interaction could be beneficial for lift enhancement, the isolated stroke simulation shows that this benefit is buried by other opposing effects, e.g. presence of downwash. The leadingedge vortex is stable during the downstroke but may shed during the upstroke. Finally, the full-body simulation result shows that the effects of wing-wing interaction and wing-body interaction are small.

Flight mechanics and control of escape manoeuvres in hummingbirds II. Aerodynamic force production, flight control and performance limitations

“…Our calculations showed that a hovering downstroke generated more than twice the lift of an upstroke (two times for magnificent hummingbirds and 2.7 times for black-chinned hummingbirds), consistent with previous studies (Song et al, 2014b;Warrick et al, 2005). We attribute this disparity between half strokes to spanwise twist of the wing, which was greater during upstroke (Cheng et al, 2016).…”

“…It has been argued that the limits may derive from physiological constraints in muscle contractile force and speed, anatomical constraints of wing motion or aerodynamic constraints (Altshuler et al, 2010a;Ellington, 1991). For the majority of these studies (Chai and Millard, 1997;Dickinson et al, 1998;Fry et al, 2005), muscle-specific power has been estimated using a simplified aerodynamic model derived from the work of Ellington (1984), which substantially underestimates power according to modern analyses based on more accurate estimation of aerodynamic forces (Song et al, 2014b;Sun and Tang, 2002).…”

Evolution of avian flight: muscles and constraints on performance

“…Present understanding is that the pectoralis via downstroke provide the majority of the work and power necessary for flapping flight [12,31] even in hummingbirds, where the upstroke contribution during hovering and slow flight is 25-30% of the total lift production [19,20,62,63]. The fibre composition of the pectoralis is remarkably uniform among most species, including only fast-twitch fibres with relatively limited variation in myosin isoforms [64,65].…”

“…Techniques that would improve confidence in the accuracy of aerodynamic estimates of power include using flow visualization (e.g. [19,62,63]) and sophisticated computational fluid dynamic (CFD) modelling [20,83].…”

Flow pattern similarities in the near wake of three bird species suggest a common role for unsteady aerodynamic effects in lift generation

“…Gardiner et al [34] simulated the wing flapping of geese to study wing kinematics and estimated lift and drag. Recently, Song et al [35] reconstructed a hummingbird's wing motion using high-speed images generating a motion-simulated wing. Yet, the flexibility, feathers and muscle activity were not considered.…”