scholarly journals Three-dimensional wing structure attenuates aerodynamic efficiency in flapping fly wings

2020 ◽  
Vol 17 (164) ◽  
pp. 20190804 ◽  
Author(s):  
Thomas Engels ◽  
Henja-Niniane Wehmann ◽  
Fritz-Olaf Lehmann
Keyword(s):  
Aerodynamic Force ◽  
Three Dimensional ◽  
Force Production ◽  
Reynolds Numbers ◽  
Dimensional Structure ◽  
Micro Computed Tomography ◽  
Venation Pattern ◽  
Aerodynamic Pressure ◽  
Inertial Loading ◽  
External Forces

The aerial performance of flying insects ultimately depends on how flapping wings interact with the surrounding air. It has previously been suggested that the wing's three-dimensional camber and corrugation help to stiffen the wing against aerodynamic and inertial loading during flapping motion. Their contribution to aerodynamic force production, however, is under debate. Here, we investigated the potential benefit of three-dimensional wing shape in three different-sized species of flies using models of micro-computed tomography-scanned natural wings and models in which we removed either the wing's camber, corrugation, or both properties. Forces and aerodynamic power requirements during root flapping were derived from three-dimensional computational fluid dynamics modelling. Our data show that three-dimensional camber has no benefit for lift production and attenuates Rankine–Froude flight efficiency by up to approximately 12% compared to a flat wing. Moreover, we did not find evidence for lift-enhancing trapped vortices in corrugation valleys at Reynolds numbers between 137 and 1623. We found, however, that in all tested insect species, aerodynamic pressure distribution during flapping is closely aligned to the wing's venation pattern. Altogether, our study strongly supports the assumption that the wing's three-dimensional structure provides mechanical support against external forces rather than improving lift or saving energetic costs associated with active wing flapping.

scholarly journals Tomography-based determination of permeability and Dupuit–Forchheimer coefficient of characteristic snow samples

2011 ◽  
Vol 57 (205) ◽  
pp. 811-816 ◽  
Author(s):  
Emilie Zermatten ◽  
Sophia Haussener ◽  
Martin Schneebeli ◽  
Aldo Steinfeld
Keyword(s):  
Mass Transport ◽  
Effective Properties ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Momentum Conservation ◽  
Micro Computed Tomography ◽  
Wide Range ◽  
Snow Microstructure ◽  
Semi Empirical

AbstractA tomography-based methodology for the mass transport characterization of snow is presented. Five samples, characteristic for a wide range of seasonal snow, are considered. Their three-dimensional (3-D) geometrical representations are obtained by micro-computed tomography and used in direct pore-level simulations to numerically solve the governing mass and momentum conservation equations, allowing for the determination of their effective permeability and Dupuit–Forchheimer coefficient. The extension to the Dupuit–coefficient is useful near the snow surface, where Reynolds numbers higher than unity can appear. Simplified semi-empirical models of porous media are also examined. The methodology presented allows for the determination of snow’s effective mass transport properties, which are strongly dependent on the snow microstructure and morphology. These effective properties can, in turn, readily be used in snowpack volume-averaged (continuum) models such as strongly layered samples with macroscopically anisotropic properties.

Visualization of a pillar-shaped fiber bundle in a model needle-punched nonwoven fabric using X-ray micro-computed tomography

2016 ◽  
Vol 87 (11) ◽  
pp. 1387-1393 ◽  
Author(s):  
Tatsuya Ishikawa ◽  
KyoungHou Kim ◽  
Yutaka Ohkoshi
Keyword(s):  
Fiber Bundle ◽  
Three Dimensional ◽  
Nonwoven Fabric ◽  
Fiber Bundles ◽  
Dimensional Structure ◽  
Micro Computed Tomography ◽  
X Ray ◽  
Needle Punching ◽  
Pet Fibers ◽  
Polyethylene Fibers

In the needle-punching process, the barbs of a needle catch fibers and orient them along the thickness direction of the fabric. The oriented fibers form a pillar-shaped fiber bundle, which acts as a bonding point of the fabric. The structure of the pillar-shaped fiber bundle thus governs the mechanical properties of needle-punched nonwoven fabric, and both are largely affected by the needle-punching conditions. However, the three-dimensional structure of pillar-shaped fiber bundles and their development under different needle-punching conditions have not been revealed. In the present study, we visualized the three-dimensional structure of a pillar-shaped fiber bundle in needle-punched nonwoven fabric, employing X-ray micro-computed tomography (XCT) on the basis of the difference in the X-ray absorption coefficient between polyethylene terephthalate (PET) and polyethylene fibers. For a material density ratio of less than 1.4 and PET fibers having a diameter of 40 µm, the pillar-shaped bundles of PET fibers were visualized by erasing 20-µm polyethylene fibers in XCT images. Furthermore, we investigated the effects of the penetration depth of the needle on the development of pillar-shaped fiber bundles. The number of fibers constituting a pillar largely increased at a penetration depth of 19.0 mm, and pillars protruded from the bottom surface of the fabric and formed a stitch structure. The XCT applied in this study is thus effective in analyzing the structure of pillar-shaped fiber bundles quantitatively without affecting the structure of the nonwoven fabric.

scholarly journals Morphological facilitators for vocal learning explored through the syrinx anatomy of a basal hummingbird

2020 ◽  
Author(s):  
Amanda Monte ◽  
Alexander F. Cerwenka ◽  
Bernhard Ruthensteiner ◽  
Manfred Gahr ◽  
Daniel N. Düring
Keyword(s):  
Sound Production ◽  
Three Dimensional ◽  
Vocal Learning ◽  
Dimensional Structure ◽  
Micro Computed Tomography ◽  
Vocal Production ◽  
Precise Control ◽  
Acoustic Space ◽  
Biomechanical Factors ◽  
Intrinsic Musculature

AbstractVocal learning is a rare evolutionary trait that evolved independently in three avian clades: songbirds, parrots, and hummingbirds. Although the anatomy and mechanisms of sound production in songbirds are well understood, little is known about the hummingbird’s vocal anatomy. We use high-resolution micro-computed tomography (μCT) and microdissection to reveal the three-dimensional structure of the syrinx, the vocal organ of the black jacobin (Florisuga fusca), a phylogenetically basal hummingbird species. We identify three unique features of the black jacobin’s syrinx: (i) a shift in the position of the syrinx to the outside of the thoracic cavity and the related loss of the sterno-tracheal muscle, (ii) complex intrinsic musculature, oriented dorso-ventrally, and (iii) ossicles embedded in the medial vibratory membranes. Their syrinx morphology allows vibratory decoupling, precise control of complex acoustic parameters, and a large redundant acoustic space that may be key biomechanical factors facilitating the occurrence of vocal production learning.

Three-dimensional structure of confined swirling jets at moderately large Reynolds numbers

2008 ◽  
Vol 20 (4) ◽  
pp. 044104 ◽  
Author(s):  
E. Sanmiguel-Rojas ◽  
M. A. Burgos ◽  
C. del Pino ◽  
R. Fernandez-Feria
Keyword(s):  
Three Dimensional ◽  
Reynolds Numbers ◽  
Dimensional Structure ◽  
Swirling Jets ◽  
Three Dimensional Structure

Simulations of three-dimensional viscoelastic flows past a circular cylinder at moderate Reynolds numbers

2010 ◽  
Vol 651 ◽  
pp. 415-442 ◽  
Author(s):  
DAVID RICHTER ◽  
GIANLUCA IACCARINO ◽  
ERIC S. G. SHAQFEH
Keyword(s):  
Circular Cylinder ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Viscoelastic Flow ◽  
Dimensional Structure ◽  
Recirculation Region ◽  
Viscoelastic Flows ◽  
Cylinder Wake ◽  
Complex Flows

The results from a numerical investigation of inertial viscoelastic flow past a circular cylinder are presented which illustrate the significant effect that dilute concentrations of polymer additives have on complex flows. In particular, effects of polymer extensibility are studied as well as the role of viscoelasticity during three-dimensional cylinder wake transition. Simulations at two distinct Reynolds numbers (Re = 100 and Re = 300) revealed dramatic differences based on the choice of the polymer extensibility (L2 in the FENE-P model), as well as a stabilizing tendency of viscoelasticity. For the Re = 100 case, attention was focused on the effects of increasing polymer extensibility, which included a lengthening of the recirculation region immediately behind the cylinder and a sharp increase in average drag when compared to both the low extensibility and Newtonian cases. For Re = 300, a suppression of the three-dimensional Newtonian mode B instability was observed. This effect is more pronounced for higher polymer extensibilities where all three-dimensional structure is eliminated, and mechanisms for this stabilization are described in the context of roll-up instability inhibition in a viscoelastic shear layer.

The three-dimensional structure of the wake of a circular cylinder

1966 ◽  
Vol 25 (1) ◽  
pp. 143-164 ◽  
Author(s):  
J. H. Gerrard
Keyword(s):  
Circular Cylinder ◽  
Growth And Development ◽  
Free Stream ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
The Body ◽  
Dimensional Structure ◽  
Vortex Wake ◽  
Vortex Lines ◽  
Critical Scrutiny

A critical scrutiny of the nature of the three-dimensional characteristics of the vortex wake of a circular cylinder serves to suggest lines for further investigation and furnishes some ideas on the nature of the growth and development of these non-uniformities. It is suggested that the basic occurrence in the growth of three-dimensionality is the continuation of vortex lines, oriented more or less parallel to the body, into the direction of the free stream. The causes of this vary, as do the details of the development with the particular situation considered.Experiments were performed in a wind tunnel at Reynolds numbers based on cylinder diameter of 85, 235 and 2 × 104, at which stable, transitional and turbulent vortices were investigated.

scholarly journals Centrifugal instability of Stokes layers in crossflow: the case of a forced cylinder wake

2015 ◽  
Vol 471 (2178) ◽  
pp. 20150011 ◽  
Author(s):  
Juan D'Adamo ◽  
Ramiro Godoy-Diana ◽  
José Eduardo Wesfreid
Keyword(s):  
Three Dimensional ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Dimensional Structure ◽  
Cylinder Wake ◽  
Theoretical Frameworks ◽  
Three Dimensional Structure ◽  
Recent Experimental Study ◽  
Centrifugal Instability ◽  
Secondary Instabilities

The wake flow around a circular cylinder at Re ≈100 performing rotatory oscillations has been thoroughly discussed in the literature, mostly focusing on the modifications to the natural Bénard–von Kármán vortex street that result from the forced shedding modes locked to the rotatory oscillation frequency. The usual experimental and theoretical frameworks at these Reynolds numbers are quasi-two-dimensional, because the secondary instabilities bringing a three-dimensional structure to the cylinder wake flow occur only at higher Reynolds numbers. In this paper, we show that a three-dimensional structure can appear below the usual three-dimensionalization threshold, when forcing with frequencies lower than the natural vortex shedding frequency, at high amplitudes, as a result of a previously unreported mechanism: a pulsed centrifugal instability of the oscillating Stokes layer at the wall of the cylinder. The present numerical investigation lets us in this way propose a physical explanation for the turbulence-like features reported in the recent experimental study by the present authors.

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