Fluid-dynamic characteristics of a bristled wing

Sunada, Shigeru; Takashima, H; Hattori, Tomohiro; Yasuda, Kunio; Kawachi, Keiji

doi:10.1242/jeb.205.17.2737

Cited by 70 publications

(25 citation statements)

References 8 publications

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“…Wings with an appropriate distance between bristles (gap width) may even act as a solid surface and thus similar to a solid membrane [20]. Experimental work on translating rectangular wings with bristles confirmed this prediction [23]. Although leakiness attenuates force production, bristled wings might be beneficial in gusty exterior flows, reducing peak changes in aerodynamic force production compared to a solid surface [24].…”

Section: Introductionmentioning

confidence: 89%

Flight efficiency is a key to diverse wing morphologies in small insects

Engels

Kolomenskiy

Lehmann

2021

J. R. Soc. Interface.

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Insect wings are hybrid structures that are typically composed of veins and solid membranes. In some of the smallest flying insects, however, the wing membrane is replaced by hair-like bristles attached to a solid root. Bristles and membranous wing surfaces coexist in small but not in large insect species. There is no satisfying explanation for this finding as aerodynamic force production is always smaller in bristled than solid wings. This computational study suggests that the diversity of wing structure in small insects results from aerodynamic efficiency rather than from the requirements to produce elevated forces for flight. The tested wings vary from fully membranous to sparsely bristled and were flapped around a wing root with lift- and drag-based wing kinematic patterns and at different Reynolds numbers ( Re ). The results show that the decrease in aerodynamic efficiency with decreasing surface solidity is significantly smaller at Re = 4 than Re = 57. A replacement of wing membrane by bristles thus causes less change in energetic costs for flight in small compared to large insects. As a consequence, small insects may fly with bristled and solid wing surfaces at similar efficacy, while larger insects must use membranous wings for an efficient production of flight forces. The above findings are significant for the biological fitness and dispersal of insects that fly at elevated energy expenditures.

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Section: Introductionmentioning

confidence: 89%

Flight efficiency is a key to diverse wing morphologies in small insects

Engels

Kolomenskiy

Lehmann

2021

J. R. Soc. Interface.

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“…The membranous parts account for about 62% of the model-wing area and the brim-hair part accounts for about 38%. Sunada et al (2002) measured the lift and drag forces on a bristled model wing and a solid-plate wing of the same shape. Different wing-motion patterns were considered: azimuthally rotating (revolving) at a constant angular speed and at a constant angular acceleration;…”

Section: On the Study Limitationsmentioning

confidence: 99%

Very small insects use novel wing flapping and drag principle to generate the weight-supporting vertical force

Cheng

Sun

2018

J. Fluid Mech.

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The effect of air viscosity on the flow around an insect wing increases as insect size decreases. For the smallest insects (wing length R below 1 mm), the viscous effect is so large that lift-generation mechanisms used by their larger counterparts become ineffective. How the weight-supporting vertical force is generated is unknown. To elucidate the aerodynamic mechanisms responsible, we measure the wing kinematics of the tiny wasp Encarsia formosa (0.6 mm R) in hovering or very slow ascending flight and compute and analyze the aerodynamic forces. We find that the insects perform two unusual wing-motions. One is "rowing": the wings move fast downward and backward, like stroking oars; the other is the previously discovered Weis-Fogh 'fling'. The rowing produces 70% of the required vertical force and the Weis-Fogh 'fling' the other 30%. The oaring wing mainly produces an approximately up-pointing drag, resulting in the vertical force. Because each oaring produces a starting flow, the drag is unsteady in nature and much greater than that in steady motion at the same velocities and angles of attack. Furthermore, our computation shows that if the tiny wasps employed the usual wing kinematics of the larger insects (flapping back and forth in a horizontal plane), vertical force produced would be only 1/3 of that by the real wing kinematics; i.e. they must use the special wing movements to overcome the problem of large viscous effects encountered by the commonly used flapping kinematics. We for the first time observe very small insects using drag to support their weight and explain how a net vertical force is generated when the drag principle is applied.Although the wing of an insect beats at high frequency (usually above 100 Hz), the velocity of the wing relative the undisturbed air is small, owing to the small wing-length. As a result, the vertical force coefficient of the wing required to balance the weight is relatively high; the mean vertical force coefficient required is around 2

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“…It is important to highlight that the use of different averaging definitions for the velocity (2) and for the pressure (3) in the continuity of the stresses results to be appropriate thanks to presence of the porosity φ in the expression of the boundary condition. In the following, the superscript • , which indicate non-dimensional quantities, and the average brackets • will be omitted for sake of brevity.…”

Section: A Flow Configuration and Governing Equationsmentioning

confidence: 99%

“…Additionally, several minute insects such as the thrips (Thysanoptera) use hairy appendages for feeding and locomotion. These filaments-made wings have convenient lift to weight and lift to drag ratios with respect an impervious wing [2] and are typically modeled as porous rectangular cylinders [3]. In a similar fashion, the seeds of taraxacum (commonly known as dandelions) and of tragopon, are transported by the wind thanks to a particular umbrella-like extensions called pappus, which can be seen as the equivalent of a parachute.…”

Section: Introductionmentioning

confidence: 99%

Suppression of von Kármán vortex streets past porous rectangular cylinders

et al. 2018

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Although the stability properties of the wake past impervious bluff bodies have been widely examined in the literature, similar analyses regarding the flow around and through porous ones are still lacking. In this work, the effect of the porosity and permeability on the wake patterns of porous rectangular cylinders is numerically investigated at low to moderate Reynolds numbers in the framework of direct numerical simulation combined with local and global stability analyses.A modified Darcy-Brinkman formulation [1] is employed here so as to describe the flow behavior inside the porous media, where also the convective terms are retained to correctly account for the inertial effects at high values of permeability. Different aspect ratios of the cylinder are considered, varying the thickness-to-height ratios, t/d, from 0.01 (flat plate) to 1.0 (square cylinder).The results show that the permeability of the bodies has a strong effect in modifying the characteristics of the wakes and of the associated flow instabilities, while the porosity weakly affects the resulting flow patterns. In particular, the fluid flows through the porous bodies and, thus, as the permeability is progressively increased, the recirculation regions, initially attached to the rear part of the bodies, at first detach from the body and, eventually, disappear even in the near wakes.Global stability analyses lead to the identification of critical values of the permeability above which any linear instability is prevented. Moreover, a different scaling of the non-dimensional permeability allows to identify a general threshold for all the configurations here studied that ensures the suppression of vortex shedding, at least in the considered parameter space. arXiv:1805.11862v1 [physics.flu-dyn] 30 May 2018

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Fluid-dynamic characteristics of a bristled wing

Cited by 70 publications

References 8 publications

Flight efficiency is a key to diverse wing morphologies in small insects

Flight efficiency is a key to diverse wing morphologies in small insects

Very small insects use novel wing flapping and drag principle to generate the weight-supporting vertical force

Suppression of von Kármán vortex streets past porous rectangular cylinders

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