Numerical Simulations of the Clap-Fling-Sweep Mechanism of Hovering Insects

The Lighthill-Weis-Fogh clap-fling-sweep mechanism is a movement used by some insects to improve their flight performance. As first suggested by Lighthill (1973), this mechanism allows large circulations around the wings to be established immediately as they start to move. Initially, the wings are clapped. Then they fling open like a book, and a non-zero circulation is established around each of them. Thus one wing can be considered as the starting vortex for the other. Then they sweep apart, carrying these bound vortices and generating lift. Since the insect wings have relatively low aspect ratio and rotate, 3d effects are important, such as spanwise flow and stabilization of the leading edge vortices (Maxworthy, 2007). To explore these effects, we perform direct numerical simulations of flapping wings, using a pseudo-spectral method with volume penalization. Comparing 2d and 3d simulations for the same setup clarifies the role of the three-dimensionality of the wake. Our results show that the 2d approximation describes very well the flow during fling, when the wings are near, but 3d effects become crucial when the wings move far apart. Possible extensions of the numerical method for modeling the interaction with thin elastic wings using FSI will also be presented.

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The Functional Role of Wing Corrugations in Living Systems

Journal of Fluids Engineering ◽

10.1115/1.3242550 ◽

1986 ◽

Vol 108 (1) ◽

pp. 93-97 ◽

Cited By ~ 22

Author(s):

R. H. Buckholz

Keyword(s):

Reynolds Number ◽

Functional Role ◽

Separated Flow ◽

Leading Edge ◽

Flow Region ◽

Wing Surface ◽

Living Systems ◽

Recirculation Region ◽

Insect Wings

Questions concerning the functional role of spanwise wing corrugation in living systems are experimentally investigated. Attention was initially directed to this problem by observation of the irregular shape of many insect wings as well as other studies indicating higher lift on these wings. First, a flow visualization scheme was used to observe and photograph streamlines around two different wing sections. One of these, a sheet metal model with geometry matching that of a butterfly wing, was studied at a chord Reynolds number of 1500 and at a Reynolds number of 80 based on corrugation depth. A steady-state recirculation region near the model leading edge was found, and the separated flow region above this recirculation zone formed a laminar reattachment to the model. A second thicker wing was corrugated on the upper surface. Closed streamlines inside these upper surface corrugations were photographed at Reynolds numbers of 8000 and 3800 based on chord length, and 200 and 90 based on corrugation depth. Reductions in pressures on the corrugated upper wing surface relative to a smooth upper wing surface were then measured.

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Numerical Flow Analysis in a Subsonic Vaned Radial Diffuser With Leading Edge Redesign

Volume 1: Aircraft Engine; Marine; Turbomachinery; Microturbines and Small Turbomachinery ◽

10.1115/97-gt-185 ◽

1997 ◽

Author(s):

E. Casartelli ◽

A. P. Saxer ◽

G. Gyarmathy

Keyword(s):

Static Pressure ◽

Flow Analysis ◽

Pressure Rise ◽

Leading Edge ◽

Inverse Design ◽

Navier Stokes ◽

Characteristic Lines ◽

3D Effects ◽

Design Software ◽

2D And 3D

The flow field in a subsonic vaned radial diffuser of a single stage centrifugal compressor is numerically investigated using a 3D Navier-Stokes solver (TASCflow) and a 2D analysis & inverse-design software package (MISES). The vane geometry is modified in the leading edge area (2D blade shaping) using MISES, without changing the diffuser throughflow characteristics. An analysis of the 2D and 3D effects of two redesigns on the flow in each of the diffuser subcomponents is performed in terms of static pressure recovery, total pressure loss production and secondary flow reduction. The computed characteristic lines are compared with measurements, which confirm the improvement obtained by the leading edge redesign in terms of increased pressure rise and operating range.

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Lift enhancement by bats' dynamically changing wingspan

Journal of The Royal Society Interface ◽

10.1098/rsif.2015.0821 ◽

2015 ◽

Vol 12 (113) ◽

pp. 20150821 ◽

Cited By ~ 11

Author(s):

Shizhao Wang ◽

Xing Zhang ◽

Guowei He ◽

Tianshu Liu

Keyword(s):

Numerical Simulations ◽

Nonlinear Interaction ◽

Mechanical Energy ◽

Leading Edge ◽

Direct Numerical Simulations ◽

Flow Structures ◽

Vortical Structures ◽

Geometrical Effect ◽

Lift Enhancement

This paper elucidates the aerodynamic role of the dynamically changing wingspan in bat flight. Based on direct numerical simulations of the flow over a slow-flying bat, it is found that the dynamically changing wingspan can significantly enhance the lift. Further, an analysis of flow structures and lift decomposition reveal that the elevated vortex lift associated with the leading-edge vortices intensified by the dynamically changing wingspan considerably contributed to enhancement of the time-averaged lift. The nonlinear interaction between the dynamically changing wing and the vortical structures plays an important role in the lift enhancement of a flying bat in addition to the geometrical effect of changing the lifting-surface area in a flapping cycle. In addition, the dynamically changing wingspan leads to the higher efficiency in terms of generating lift for a given amount of the mechanical energy consumed in flight.

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High‐resolution numerical simulations of electrophoresis using the Fourier pseudo‐spectral method

Electrophoresis ◽

10.1002/elps.202000259 ◽

2020 ◽

Author(s):

Prateek Gupta ◽

Supreet Singh Bahga

Keyword(s):

High Resolution ◽

Numerical Simulations ◽

Spectral Method ◽

Pseudo Spectral Method ◽

Pseudo Spectral

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Compressible MHD in Spherical Geometry

International Astronomical Union Colloquium ◽

10.1017/s0252921100079434 ◽

1991 ◽

Vol 130 ◽

pp. 80-85

Author(s):

Lorenzo Valdettaro ◽

Maurice Meneguzzi

Keyword(s):

Magnetic Field ◽

Temperature Scale ◽

Spherical Geometry ◽

Prandtl Numbers ◽

Pseudo Spectral Method ◽

Dynamo Effect ◽

Rayleigh Numbers ◽

Pseudo Spectral ◽

The Magnetic Field

AbstractThe generation of magnetic field by a conducting, compressible fluid inside a spherical shell is studied by direct numerical simulations. A pseudo-spectral method is used in order to resolve accurately all the scales present in the problem. The range of parameters considered is the following: a unit Prandtl number, Rayleigh numbers up to 100 times critical, Taylor number 625, an aspect ratio of 2, a Mach number slightly less than 1, and pressure and temperature scale heights of the order of the thickness of the shell. A dynamo effect is observed for magnetic Prandtl numbers larger than 1. We present the properties of the turbulent flow, the role of the helicity and of the differential rotation in the enhancement of the magnetic field, and the spectral properties of the flow fields.

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