Turbulent mixing in uniform channels of irregular cross-section

It is argued on the basis of exact solutions for uniform vortices in straining fields that vortices of finite cross-section in a row will disintegrate if the spacing is too small. The results are applied to the organized vortex structures observed in turbulent mixing layers. An explanation is provided for the disappearance of these structures as they move downstream and it is deduced that the ratio of average spacing to width should be about 3·5, the width being defined by the maximum slope of the mean velocity. It is shown in an appendix that walls have negligible effect.

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Energetics of a linear array of hollow vortices of finite cross-section

Journal of Fluid Mechanics ◽

10.1017/s0022112080000523 ◽

1980 ◽

Vol 99 (1) ◽

pp. 97-100 ◽

Cited By ~ 2

Author(s):

Gregory R. Baker

Keyword(s):

Cross Section ◽

Ideal Fluid ◽

Turbulent Mixing ◽

Linear Array ◽

Mixing Layer ◽

Vortex Structures ◽

Turbulent Mixing Layer

The energetics of a linear array of hollow or stagnant-cored vortices of finite cross-section in an ideal fluid is studied in this paper. The results are useful in a discussion of the amalgamation of vortex structures in a turbulent mixing layer.

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Implementation of a Mixing Length Turbulence Formulation Into the Dynamic Wake Meandering Model

Journal of Solar Energy Engineering ◽

10.1115/1.4006038 ◽

2012 ◽

Vol 134 (2) ◽

Cited By ~ 13

Author(s):

Rolf-Erik Keck ◽

Dick Veldkamp ◽

Helge Aagaard Madsen ◽

Gunner Larsen

Keyword(s):

Cross Section ◽

Turbulent Mixing ◽

Eddy Viscosity ◽

High Fidelity ◽

Mixing Length ◽

Two Dimensional ◽

Wake Region ◽

Mean Velocity ◽

The Mean ◽

The Difference

The work presented in this paper focuses on improving the description of wake evolution due to turbulent mixing in the dynamic wake meandering (DWM) model. From wake investigations performed with high-fidelity actuator line simulations carried out in ELLIPSYS3D, it is seen that the current DWM description, where the eddy viscosity is assumed to be constant in each cross-section of the wake, is insufficient. Instead, a two-dimensional eddy viscosity formulation is proposed to model the shear layer generated turbulence in the wake, based on the classical mixing length model. The performance of the modified DWM model is verified by comparing the mean wake velocity distribution with a set of ELLIPSYS3D actuator line calculations. The standard error (defined as the standard deviation of the difference between the mean velocity field of the DWM and the actuator line model), in the wake region extending from 3 to 12 diameters behind the rotor, is reduced by 27% by using the new eddy viscosity formulation.

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Experimental and Numerical Investigation of the Growth of an Air/SF6 Turbulent Mixing Zone in a Shock Tube

Journal of Fluids Engineering ◽

10.1115/1.4036369 ◽

2017 ◽

Vol 139 (9) ◽

Cited By ~ 1

Author(s):

J. Griffond ◽

J.-F. Haas ◽

D. Souffland ◽

G. Bouzgarrou ◽

Y. Bury ◽

...

Keyword(s):

Shock Wave ◽

Shock Tube ◽

Cross Section ◽

Turbulent Mixing ◽

Test Chamber ◽

Weak Dependence ◽

Mixing Zone ◽

Nitrocellulose Membrane ◽

Mesh Spacing ◽

Zone Growth

Shock-induced mixing experiments have been conducted in a vertical shock tube of 130 mm square cross section located at ISAE. A shock wave traveling at Mach 1.2 in air hits a geometrically disturbed interface separating air and SF6, a gas five times heavier than air, filling a chamber of length L up to the end of the shock tube. Both gases are initially separated by a 0.5 μm thick nitrocellulose membrane maintained parallel to the shock front by two wire grids: an upper one with mesh spacing equal to either ms = 1.8 mm or 12.1 mm, and a lower one with a mesh spacing equal to ml = 1 mm. Weak dependence of the mixing zone growth after reshock (interaction of the mixing zone with the shock wave reflected from the top end of the test chamber) with respect to L and ms is observed despite a clear imprint of the mesh spacing ms in the schlieren images. Numerical simulations representative of these configurations are conducted: the simulations successfully replicate the experimentally observed weak dependence on L, but are unable to show the experimentally observed independence with respect to ms while matching the morphological features of the schlieren pictures.

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XUV Absorption Spectra of Carbon Ions

International Astronomical Union Colloquium ◽

10.1017/s0252921100107444 ◽

1988 ◽

Vol 102 ◽

pp. 71-73

Author(s):

E. Jannitti ◽

P. Nicolosi ◽

G. Tondello

Keyword(s):

Absorption Spectra ◽

Cross Section ◽

Theoretical Calculations ◽

Photoionization Cross Section ◽

Carbon Ions

AbstractThe photoabsorption spectra of the carbon ions have been obtained by using two laser-produced plasmas. The photoionization cross-section of the CV has been absolutely measured and the value at threshold, σ=(4.7±0.5) × 10−19cm2, as well as its behaviour at higher energies agrees quite well with the theoretical calculations.

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Elastic Scattering in Electron Microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100071703 ◽

1973 ◽

Vol 31 ◽

pp. 252-253

Author(s):

J. Langmore ◽

M. Isaacson ◽

J. Wall ◽

A. V. Crewe

Keyword(s):

Electron Microscopy ◽

Elastic Scattering ◽

Cross Section ◽

Quantum Noise ◽

Dark Field ◽

Elastic Cross Section ◽

Biological Molecules ◽

Dark Field Microscopy ◽

Field Systems ◽

Effects Of Radiation

High resolution dark field microscopy is becoming an important tool for the investigation of unstained and specifically stained biological molecules. Of primary consideration to the microscopist is the interpretation of image Intensities and the effects of radiation damage to the specimen. Ignoring inelastic scattering, the image intensity is directly related to the collected elastic scattering cross section, σɳ, which is the product of the total elastic cross section, σ and the eficiency of the microscope system at imaging these electrons, η. The number of potentially bond damaging events resulting from the beam exposure required to reduce the effect of quantum noise in the image to a given level is proportional to 1/η. We wish to compare η in three dark field systems.

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A New Approach to the Demonstration of Oxidase-Localization Using Tannic Acid Or Catechin

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100073933 ◽

1973 ◽

Vol 31 ◽

pp. 698-699

Author(s):

V. Mizuhira ◽

Y. Futaesaku

Keyword(s):

Cross Section ◽

Tannic Acid ◽

Elastic Fiber ◽

The Other ◽

New Approach ◽

Tissue Block ◽

Active Reaction ◽

The Cross

Previously we reported that tannic acid is a very effective fixative for proteins including polypeptides. Especially, in the cross section of microtubules, thirteen submits in A-tubule and eleven in B-tubule could be observed very clearly. An elastic fiber could be demonstrated very clearly, as an electron opaque, homogeneous fiber. However, tannic acid did not penetrate into the deep portion of the tissue-block. So we tried Catechin. This shows almost the same chemical natures as that of proteins, as tannic acid. Moreover, we thought that catechin should have two active-reaction sites, one is phenol,and the other is catechole. Catechole site should react with osmium, to make Os- black. Phenol-site should react with peroxidase existing perhydroxide.

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Electron Irradiation Effects in Polyoxymethylene Crystals Grown Inside Trioxane Crystals

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010006444x ◽

1971 ◽

Vol 29 ◽

pp. 78-79

Author(s):

J. P. Colson ◽

D. H. Reneker

Keyword(s):

Cross Section ◽

Cross Sections ◽

Detailed Examination ◽

The Other ◽

Electron Micrograph ◽

Irradiation Effects ◽

Threefold Axis ◽

Typical Sample ◽

Polymer Crystals ◽

Chain Axis

Polyoxymethylene (POM) crystals grow inside trioxane crystals which have been irradiated and heated to a temperature slightly below their melting point. Figure 1 shows a low magnification electron micrograph of a group of such POM crystals. Detailed examination at higher magnification showed that three distinct types of POM crystals grew in a typical sample. The three types of POM crystals were distinguished by the direction that the polymer chain axis in each crystal made with respect to the threefold axis of the trioxane crystal. These polyoxymethylene crystals were described previously.At low magnifications the three types of polymer crystals appeared as slender rods. One type had a hexagonal cross section and the other two types had rectangular cross sections, that is, they were ribbonlike.

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Freeze-Fracture Replication of Frozen Outer Segments of Rat Retinal Rods

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100063871 ◽

1969 ◽

Vol 27 ◽

pp. 392-393

Author(s):

Thomas S. Leeson ◽

C. Roland Leeson

Keyword(s):

Electron Microscopy ◽

Cross Section ◽

Outer Segment ◽

Freeze Fracture ◽

X Ray Diffraction ◽

X Ray ◽

Outer Segments ◽

Retinal Rods ◽

Temperature Electron ◽

Freeze Etching

Numerous previous studies of outer segments of retinal receptors have demonstrated a complex internal structure of a series of transversely orientated membranous lamellae, discs, or saccules. In cones, these lamellae probably are invaginations of the covering plasma membrane. In rods, however, they appear to be isolated and separate discs although some authors report interconnections and some continuities with the surface near the base of the outer segment, i.e. toward the inner segment. In some species, variations have been reported, such as longitudinally orientated lamellae and lamellar whorls. In cross section, the discs or saccules show one or more incisures. The saccules probably contain photolabile pigment, with resulting potentials after dipole formation during bleaching of pigment. Continuity between the lamina of rod saccules and extracellular space may be necessary for the detection of dipoles, although such continuity usually is not found by electron microscopy. Particles on the membranes have been found by low angle X-ray diffraction, by low temperature electron microscopy and by freeze-etching techniques.

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