Hummingbirds generate bilateral vortex loops during hovering: evidence from flow visualization

Pournazeri, Sam; Segre, Paolo S.; Princevac, Marko; Altshuler, Douglas L.

doi:10.1007/s00348-012-1439-5

Cited by 28 publications

(31 citation statements)

References 42 publications

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“…In asymmetric hovering, the wake has been postulated to consist of a single vortex loop shed as the result of a powerful downstroke and in the case of an inactive upstroke no vortices are shed during the upstroke (figure 1c). Flow visualization of wakes in hummingbirds suggest the model in figure 1b as most plausible [4,12], or a more complex arrangement of bi-lateral vortices [14]. An aerodynamic analysis based on wingbeat kinematics of a hovering pied flycatcher (Ficedula hypeuca) suggested an active downstroke and an inactive upstroke [5], as expected for asymmetric hovering with an inclined stroke plane.…”

Section: Introductionmentioning

confidence: 78%

The wake of hovering flight in bats

Håkansson

Hedenström

Winter

et al. 2015

J. R. Soc. Interface.

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Hovering means stationary flight at zero net forward speed, which can be achieved by animals through muscle powered flapping flight. Small bats capable of hovering typically do so with a downstroke in an inclined stroke plane, and with an aerodynamically active outer wing during the upstroke. The magnitude and time history of aerodynamic forces should be reflected by vorticity shed into the wake. We thus expect hovering bats to generate a characteristic wake, but this has until now never been studied. Here we trained nectar-feeding bats, Leptonycteris yerbabuenae, to hover at a feeder and using time-resolved stereoscopic particle image velocimetry in conjunction with high-speed kinematic analysis we show that hovering nectar-feeding bats produce a series of bilateral stacked vortex loops. Vortex visualizations suggest that the downstroke produces the majority of the weight support, but that the upstroke contributes positively to the lift production. However, the relative contributions from downstroke and upstroke could not be determined on the basis of the wake, because wake elements from down-and upstroke mix and interact. We also use a modified actuator disc model to estimate lift force, power and flap efficiency. Based on our quantitative wake-induced velocities, the model accounts for weight support well (108%). Estimates of aerodynamic efficiency suggest hovering flight is less efficient than forward flapping flight, while the overall energy conversion efficiency (mechanical power output/metabolic power) was estimated at 13%.

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Section: Introductionmentioning

confidence: 78%

The wake of hovering flight in bats

Håkansson

Hedenström

Winter

et al. 2015

J. R. Soc. Interface.

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“…However, as observed in the smoke line video, the finch had a start vortex that began independently on both wings, just like the dove (supplementary material Movie 1). As a consequence of this right and left wingindependent vortex ring structure (Pournazeri et al, 2013), the measured circulation in the sagittal plane dorsal to the bird was 20-40% lower in the finch at the start of downstroke, suggesting a relatively smaller time interval over which circulation was created. This smaller time frame was a consequence of the wings of the finch beginning the downstroke farther from the midline of the bird (Fig.…”

Section: Aerodynamicsmentioning

confidence: 89%

Kinematics and aerodynamics of avian upstrokes during slow flight

Crandell

Tobalske

2015

Journal of Experimental Biology

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Slow flight is extremely energetically costly per unit time, yet highly important for takeoff and survival. However, at slow speeds it is presently thought that most birds do not produce beneficial aerodynamic forces during the entire wingbeat: instead they fold or flex their wings during upstroke, prompting the long-standing prediction that the upstroke produces trivial forces. There is increasing evidence that the upstroke contributes to force production, but the aerodynamic and kinematic mechanisms remain unknown. Here, we examined the wingbeat cycle of two species: the diamond dove (Geopelia cuneata) and zebra finch (Taeniopygia guttata), which exhibit different upstroke styles -a wingtip-reversal and flexed-wing upstroke, respectively. We used a combination of particle image velocimetry and near-wake streamline measures alongside detailed 3D kinematics. We show that during the middle of the wingtip-reversal upstroke, the hand-wing has a high angular velocity (15.3±0.8 deg ms ). The flexed-wing upstroke, in contrast, has low wingtip speed during mid-upstroke. Instead, later in the stroke cycle, during the transition from upstroke to downstroke, it exhibits higher angular velocities (45.5±13.8 deg ms ). In contrast, the flexed-wing upstroke imparts minimal momentum. Clap and peel in the dove enhances the time course for circulation production on the wings, and provides new evidence of convergent evolution on time-varying aerodynamic mechanisms during flapping in insects and birds.

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“…Hummingbird hovering kinematics are characterized by high stroke amplitudes [19,20], over which the wing translates for several chord lengths. This feature makes hummingbird hovering kinematics a suitable subject for quasi-steady analysis with revolving wings, in particular during midstroke when wing acceleration is zero and the time-history effects of stroke reversal are weak [21][22][23][24][25].…”

Section: Introductionmentioning

confidence: 99%

Hummingbird wing efficacy depends on aspect ratio and compares with helicopter rotors

Kruyt

Quicazan-Rubio

Heijst

et al. 2014

J. R. Soc. Interface.

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120

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Hummingbirds are the only birds that can sustain hovering. This unique flight behaviour comes, however, at high energetic cost. Based on helicopter and aeroplane design theory, we expect that hummingbird wing aspect ratio (AR), which ranges from about 3.0 to 4.5, determines aerodynamic efficacy. Previous quasi-steady experiments with a wing spinner set-up provide no support for this prediction. To test this more carefully, we compare the quasi-steady hover performance of 26 wings, from 12 hummingbird taxa. We spun the wings at angular velocities and angles of attack that are representative for every species and measured lift and torque more precisely. The power (aerodynamic torque Â angular velocity) required to lift weight depends on aerodynamic efficacy, which is measured by the power factor. Our comparative analysis shows that AR has a modest influence on lift and drag forces, as reported earlier, but interspecific differences in power factor are large. During the downstroke, the power required to hover decreases for larger AR wings at the angles of attack at which hummingbirds flap their wings ( p , 0.05). Quantitative flow visualization demonstrates that variation in hover power among hummingbird wings is driven by similar stable leading edge vortices that delay stall during the down-and upstroke. A side-byside aerodynamic performance comparison of hummingbird wings and an advanced micro helicopter rotor shows that they are remarkably similar.

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Hummingbirds generate bilateral vortex loops during hovering: evidence from flow visualization

Cited by 28 publications

References 42 publications

The wake of hovering flight in bats

The wake of hovering flight in bats

Kinematics and aerodynamics of avian upstrokes during slow flight

Hummingbird wing efficacy depends on aspect ratio and compares with helicopter rotors

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