Three-dimensionality of organized structures in a plane turbulent wake

1989 ◽  
Vol 206 ◽  
pp. 375-404 ◽  
Author(s):  
Michio Hayakawa ◽  
Fazle Hussain
Keyword(s):  
Cross Sections ◽  
Coherent Structures ◽  
Near Field ◽  
Spatial Coherence ◽  
Three Dimensional ◽  
Quantitative Measure ◽  
Turbulent Wake ◽  
Topological Features ◽  
Plane Wake ◽  
Plane Turbulent Wake

This paper describes a quantitative study of the three-dimensional nature of organized motions in a turbulent plane wake. Coherent structures are detected from the instantaneous, spatially phase-correlated vorticity field using certain criteria based on size, strength and geometry of vortical structures. With several combinations of X-wire rakes, vorticity distributions in the spanwise and transverse planes are measured in the intermediate region (10d [les ] x [les ] 40d) of the plane turbulent wake of a circular cylinder at a Reynolds number of 13000 based on the cylinder diameter d. Spatial correlations of smoothed vorticity signals as well as phase-aligned ensemble-averaged vorticity maps over structure cross-sections yield a quantitative measure of the spatial coherence and geometry of organized structures in the fully turbulent field. The data demonstrate that the organized structures in the nominally two-dimensional wake exhibit significant three-dimensionality even in the near field. Using instantaneous velocity and vorticity maps as well as correlations of vorticity distributions in different planes, some topological features of the dominant coherent structures in a plane wake are inferred.

NESTED INVARIANT 3-TORI EMBEDDED IN A SEA OF CHAOS IN A QUASIPERIODIC FLUID FLOW

2009 ◽  
Vol 19 (07) ◽  
pp. 2181-2191 ◽  
Author(s):  
HOPE L. WEISS ◽  
ANDREW J. SZERI
Keyword(s):  
Fixed Point ◽  
Fluid Flow ◽  
Cross Sections ◽  
Coherent Structures ◽  
Three Dimensional ◽  
Elliptic Type ◽  
Two Phase ◽  
Dimensional Phase Space ◽  
Hyperbolic Fixed Point ◽  
Stream Functions

Nested invariant 3-tori surrounding a torus braid of elliptic type are found to exist in a model of a fluid flow with quasiperiodic forcing. The Hamiltonian describing the system is given by the superposition of two steady stream functions, one with an elliptic fixed point and the other with a coincident hyperbolic fixed point. The superposition, modulated by two incommensurate frequencies, yields an elliptic torus braid at the location of the fixed point. The system is suspended in a four-dimensional phase space (two space and two phase directions). To analyze this system we define two three-dimensional, global, Poincaré sections of the flow. The coherent structures (cross-sections of nested 2 tori) are found each to have a fractal dimensional of two, in each Poincaré cross-section. This framework has applications to tidal and other mixing problems of geophysical interest.

The evolution of the coherent structures in a uniformly distorted plane turbulent wake

1995 ◽  
Vol 291 ◽  
pp. 299-322 ◽  
Author(s):  
G. A. Kopp ◽  
J. G. Kawall ◽  
J. F. Keffer
Keyword(s):  
Coherent Structures ◽  
Large Scale ◽  
Turbulent Wake ◽  
Entrainment Rate ◽  
Rapid Distortion Theory ◽  
Vortex Model ◽  
Pattern Recognition Analysis ◽  
Preservation Theory ◽  
Far Wake ◽  
Plane Turbulent Wake

A plane turbulent wake generated by a flat plate is subjected to a uniform distortion. It is observed that nearly two-dimensional, quasi-periodic coherent structures dominate the distorted wake. Rapid distortion theory, applied to a kinematic vortex model of the coherent structures in the undistorted far wake, predicts many of the effects revealed by a hot-wire anemometry/pattern-recognition analysis of these structures. Specifically, rapid distortion theory predicts reasonably well the observed changes in the ensemble-averaged velocity patterns and the disproportionate amplification of the large-scale coherent structures relative to the smaller-scale ‘isotropic’ eddies. These results are consistent with the view that self-preservation of the distorted wake is not possible because of the selective amplification of the coherent structures, which control the development of the wake. As well, the entrainment rate in the distorted wake increases at a rate greater than that predicted by the self-preservation theory.

Coherent Structures in a Three-Dimensional Wall Jet

1990 ◽  
Vol 112 (4) ◽  
pp. 462-467 ◽  
Author(s):  
Hisashi Matsuda ◽  
Sei-ichi Iida ◽  
Michio Hayakawa
Keyword(s):  
Coherent Structures ◽  
Large Scale ◽  
Near Field ◽  
Three Dimensional ◽  
Sampling Technique ◽  
Wall Jet ◽  
Structure Model ◽  
Streamwise Vortices ◽  
Lateral Velocity ◽  
Circular Nozzle

The formation mechanism of streamwise vortices in the near field of the three-dimensional wall jet discharging from a circular nozzle along a flat plate is studied experimentally using a conditional sampling technique. Ensemble-averages of the lateral velocity component indicate the presence of large-scale horseshoe-like structures, whose legs are inclined and stretched to form the streamwise vortices in the mixing region of the jet. Based on the present result, a coherent structure model for the near field of the wall jet is proposed.

Evolution of coherent structures in the plane turbulent wake of a porous body

1993 ◽  
Vol 7 (2) ◽  
pp. 151
Author(s):  
Z. Huang ◽  
J.G. Kawall ◽  
J.F. Keffer ◽  
J.A. Ferré
Keyword(s):  
Coherent Structures ◽  
Porous Body ◽  
Turbulent Wake ◽  
Plane Turbulent Wake

scholarly journals Spatial coherence of light inside three-dimensional media

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Marco Leonetti ◽  
Lorenzo Pattelli ◽  
Simone De Panfilis ◽  
Diederik S. Wiersma ◽  
Giancarlo Ruocco
Keyword(s):  
Random Media ◽  
Degrees Of Freedom ◽  
Near Field ◽  
Spatial Coherence ◽  
Three Dimensional ◽  
Theoretical Description ◽  
Spatially Resolved ◽  
Theoretical Predictions ◽  
Physical Access ◽  
Physical Phenomena

AbstractSpeckle is maybe the most fundamental interference effect of light in disordered media, giving rise to fascinating physical phenomena and cutting edge applications. While speckle formed outside a sample is easily measured and analysed, true bulk speckle, as formed inside random media, is difficult to investigate directly due to the obvious issue of physical access. Furthermore, its proper theoretical description poses enormous challenges. Here we report on the first direct measurements of spatially resolved intensity correlations of light inside a disordered medium, using embedded DNA strings decorated with emitters separated by a controlled nanometric distance. Our method provides in situ access to fundamental properties of bulk speckles as their size and polarization degrees of freedom, both of which are found to deviate significantly from theoretical predictions. The deviations are explained, by comparison with rigorous numerical calculations, in terms of correlations among polarization components and non-universal near-field contributions at the nanoscale.

The dynamics of the near field of strong jets in crossflows

1989 ◽  
Vol 200 ◽  
pp. 95-120 ◽  
Author(s):  
Sergio L. V. Coelho ◽  
J. C. R. Hunt
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Near Field ◽  
Three Dimensional ◽  
Vortex Sheet ◽  
Transverse Component ◽  
Viscous Effects ◽  
Mean Velocity ◽  
Pressure Drag ◽  
The Cross

An inviscid three-dimensional vortex-sheet model for the near field of a strong jet issuing from a pipe into a crossflow is derived. The solution for this model shows that the essential mechanisms governing this idealized flow are the distortion of the main transverse vorticity by the generation of additional axial and transverse vorticity within the pipe owing to the pressure gradients induced by the external flow, and the convection of both components of vorticity from the upwind side of the jet to its downwind side.The deformation of the cross-section of the jet which is predicted by this model is compared with the deformation predicted by the commonly used time-dependent two-dimensional vortex-sheet model. Differences arise because the latter model does not take into account the effects of the transport of the transverse component of vorticity. The complete three-dimensional vortex-sheet model leads to a symmetrical deformation of the jet cross-section and no overall deflection of the jet in the direction of the stream.To account for viscous effects, the initial region of a strong jet issuing into a uniform crossflow is modelled as an entraining three-dimensional vortex sheet, which acts like a sheet of vortices and sinks, redistributing the vorticity in the bounding shear layer and inducing non-symmetrical deformations of the cross-section of the jet. This leads to a deflection of the jet in the direction of the stream, and the loci of the centroids of the cross-sections of the jet describe a quadratic curve.Deformations predicted by each of the three models are compared with measurements obtained from photographs of the cross-sections of a jet of air emerging into a uniform crossflow in a wind tunnel. Mean velocity measurements around the jet made with a hot-wire anemometer agree with the theory; they clearly invalidate models of jets based on ‘pressure drag’.

scholarly journals Coherent Streamwise Vortex Structure of a Three-Dimensional Wall Jet

Fluids ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 35
Author(s):  
Lhendup Namgyal ◽  
Joseph W. Hall
Keyword(s):  
Coherent Structures ◽  
Near Field ◽  
Three Dimensional ◽  
Streamwise Vortex ◽  
Relative Strength ◽  
Vortex Structures ◽  
Wall Jet ◽  
Streamwise Vorticity ◽  
Lateral Velocity ◽  
Near Wall

The dynamics of the coherent structures in a turbulent three-dimensional wall jet with an exit Reynolds number of 250,000 were investigated using the Snapshot Proper Orthogonal Decomposition (POD). A low-dimensional reconstruction using the first 10 POD modes indicates that the turbulent flow is dominated by streamwise vortex structures that grow in size and relative strength, and that are often accompanied by strong lateral sweeps of fluid across the wall. This causes an increase in the bulging and distortions of streamwise velocity contours as the flow evolves downstream. The instantaneous streamwise vorticity computed from the reconstructed instantaneous velocities has a high level of vorticity associated with these outer streamwise vortex structures, but often has a persistent pair of counter-rotating regions located close to the wall on either side of the jet centerline. A model of the coherent structures in the wall jet is presented. In this model, streamwise vortex structures are produced in the near-field by the breakdown of vortex rings formed at the jet outlet. Separate structures are associated with the near-wall streamwise vorticity. As the flow evolves downstream, the inner near-wall structures tilt outward, while the outer streamwise structures amalgamate to form larger streamwise asymmetric structures. In all cases, these streamwise vortex structures tend to cause large lateral velocity sweeps in the intermediate and far-field regions of the three-dimensional wall jet. Further, these structures meander laterally across the jet, causing a strongly intermittent jet flow.

scholarly journals Infrared Nanoscopy and Tomography of Intracellular Structures

2021 ◽  
Author(s):  
Katerina Kanevche ◽  
David Burr ◽  
Andreas Elsaesser ◽  
Pascal-Kolja Hass ◽  
Dennis Nuernberg ◽  
...  
Keyword(s):  
Cross Sections ◽  
Infrared Radiation ◽  
Near Field ◽  
Three Dimensional ◽  
Infrared Image ◽  
Chemical Imaging ◽  
Subcellular Structure ◽  
Covalent Bonds ◽  
20 Nm ◽  
Microscopic Techniques

Abstract The few microscopic techniques that simultaneously gather morphological and chemical data often rely on the use of specific markers. To eliminate this flaw, we have developed a method of examining cellular cross sections using the imaging power of scattering-type scanning near-field optical microscopy and Fourier-transform infrared spectroscopy at a spatial resolution far beyond the diffraction limit. Herewith, nanoscale surface and volumetric chemical imaging is performed using the intrinsic contrast generated by the characteristic absorption of mid-infrared radiation by the covalent bonds. We employ infrared nanoscopy to study the subcellular structures of eukaryotic (Chlamydomonas reinhardtii) and prokaryotic (Escherichia coli) species, revealing chemically distinct regions within each cell such as the microtubular structure of the flagellum. Serial 100 nm-thick cellular cross-sections were compiled into a tomogram yielding a three-dimensional infrared image of subcellular structure distribution at 20 nm resolution. The presented methodology is able to image biological samples competing current fluorescence nanoscopy but at less interference due to the low energy of infrared radiation and the absence of labeling.

scholarly journals Low-dimensional dynamics of a turbulent axisymmetric wake

2014 ◽  
Vol 755 ◽  
Author(s):  
G. Rigas ◽  
A. R. Oxlade ◽  
A. S. Morgans ◽  
J. F. Morrison
Keyword(s):  
Vortex Shedding ◽  
Coherent Structures ◽  
Three Dimensional ◽  
Symmetry Plane ◽  
Turbulent Wake ◽  
Axisymmetric Body ◽  
The Body ◽  
Slow Rotation ◽  
Mean Pressure ◽  
Low Dimensional

AbstractThe coherent structures of a turbulent wake generated behind a bluff three-dimensional axisymmetric body are investigated experimentally at a diameter-based Reynolds number of $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}{\sim }2\times 10^5$. Proper orthogonal decomposition of base pressure measurements indicates that the most energetic coherent structures retain the structure of the symmetry-breaking laminar instabilities and are manifested as unsteady vortex shedding with azimuthal wavenumber $m={\pm }1$. In a rotating reference frame, the shedding preserves the reflectional symmetry and is linked with a reflectionally symmetric mean pressure distribution on the base. Due to a slow rotation of the symmetry plane of the turbulent wake around the axis of the body, statistical axisymmetry is recovered in the time average. The ratio of the time scales associated with the slow rotation of the symmetry plane and the vortex shedding is of order 100.

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