scholarly journals Multi-branching three-dimensional flow with substantial changes in vessel shapes

2008 ◽  
Vol 614 ◽  
pp. 329-354 ◽  
Author(s):  
R. I. BOWLES ◽  
N. C. OVENDEN ◽  
F. T. SMITH
Keyword(s):  
Three Dimensional ◽  
Longitudinal Vortex ◽  
Cross Sectional ◽  
Flow Rates ◽  
Relative Flow Rate ◽  
Wide Range ◽  
Flow Through ◽  
Sectional Shape ◽  
Area Expansion ◽  
Reversed Motion

This theoretical investigation of steady fluid flow through a rigid three-dimensional branching geometry is motivated by applications to haemodynamics in the brain especially, while the flow through a tube with a blockage or through a collapsed tube provides another motivation with a biomedical background. Three-dimensional motion without symmetry is addressed through one mother vessel to two or several daughters. A comparatively long axial length scale of the geometry leads to a longitudinal vortex system providing a slender-flow model for the complete mother-and-daughters flow response. Computational studies and subsequent analysis, along with comparisons, are presented. The relative flow rate varies in terms of an effective Reynolds number dependence, allowing a wide range of flow rates to be examined theoretically; also any rigid cross-sectional shape and ratio of cross-sectional area expansion or contraction from the mother vessel to the daughters can be accommodated in principle in both the computations and the analysis. Swirl production with substantial crossflows is found. The analysis shows that close to any carina (the ridge separating daughter vessels) or carinas at a branch junction either forward or reversed motion can be observed locally at the saddle point even though the bulk of the motion is driven forward into the daughters. The local forward or reversed motion is controlled, however, by global properties of the geometry and incident conditions, a feature which applies to any of the flow rates examined.

scholarly journals Microtubules soften due to cross-sectional flattening

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Edvin Memet ◽  
Feodor Hilitski ◽  
Margaret A Morris ◽  
Walter J Schwenger ◽  
Zvonimir Dogic ◽  
...  
Keyword(s):  
High Strain ◽  
Three Dimensional ◽  
Elastic Model ◽  
Softening Effect ◽  
Cross Sectional ◽  
Mechanical Compliance ◽  
Wide Range ◽  
Elastic Filament ◽  
New Interpretation ◽  
Effective Mechanical Properties

We use optical trapping to continuously bend an isolated microtubule while simultaneously measuring the applied force and the resulting filament strain, thus allowing us to determine its elastic properties over a wide range of applied strains. We find that, while in the low-strain regime, microtubules may be quantitatively described in terms of the classical Euler-Bernoulli elastic filament, above a critical strain they deviate from this simple elastic model, showing a softening response with increasing deformations. A three-dimensional thin-shell model, in which the increased mechanical compliance is caused by flattening and eventual buckling of the filament cross-section, captures this softening effect in the high strain regime and yields quantitative values of the effective mechanical properties of microtubules. Our results demonstrate that properties of microtubules are highly dependent on the magnitude of the applied strain and offer a new interpretation for the large variety in microtubule mechanical data measured by different methods.

Enamel Crystal Shape: History of an Idea

1987 ◽  
Vol 1 (2) ◽  
pp. 322-329 ◽  
Author(s):  
H. Warshawsky
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Cross Sections ◽  
Three Dimensional ◽  
Unit Cell ◽  
Cross Sectional ◽  
Transmission Electron ◽  
History Of ◽  
Sectional Shape ◽  
Imaging Plane

The purpose of this paper is to review evidence which casts doubt on the interpretation universally applied to hexagonal images seen in sectioned enamel. The evidence is based on two possible models to explain the hexagonal profiles seen in mammalian enamel with transmission electron microscopy. The "hexagonal ribbon" model proposes that hexagonal profiles are true cross-sections of elongated hexagonal ribbons. The "rectangular ribbon" model proposes that hexagonal profiles are caused by three-dimensional segments that are parallelepipeds contained in the Epon section. Since shadow projections of such rectangular segments give angles that are inconsistent with the hexagonal unit cell, a model based on ribbons with rhomboidal cut ends and angles of 60 and 120° is proposed. The "rhomboidal ribbon" model projects shadows with angles that are predicted by the unit cell. It is suggested that segments of such crystallites in section project as opaque hexagons on the imaging plane in routine transmission electron microscopy. Morphological observations on crystallites in sections - together with predictions from the hexagonal, rectangular, and rhomboidal ribbon models - indicate that crystallites in rat incisor enamel are flat ribbons with rhomboidal cross-sectional shape. Hexagonal images in electron micrographs of thin-sectioned enamel can result from rhomboidal-ended, parallelepiped-shaped segments of these crystallites projected and viewed as two-dimensional shadows.

scholarly journals The Influence of Flow Rate on the Wake in a Centrifugal Impeller

1982 ◽  
Author(s):  
M. W. Johnson ◽  
J. Moore
Keyword(s):  
Flow Rate ◽  
Incidence Angle ◽  
Three Dimensional ◽  
Stagnation Pressure ◽  
Centrifugal Impeller ◽  
Suction Surface ◽  
Cross Sectional ◽  
Flow Rates ◽  
Pressure Losses ◽  
Compressor Impeller

Three-dimensional flows and their influence on the stagnation pressure losses in a centrifugal compressor impeller have been studied. All 3 mutally perpendicular components of relative velocity and stagnation pressure on 5 cross-sectional planes, between the inlet and outlet of a 1 m dia shrouded impeller running at 500 rpm were measured. Comparisons were made between results for a flow rate corresponding to nearly zero incidence angle and two other flows, with increased and reduced flow rates. These detailed measurements show how the position of separation of the shroud boundary layer moved downstream and the wake’s size decreased, as the flow rate was increased. The wake’s location, at the outlet of the impeller, was also observed to move from the suction surface at the lowest flow rate, to the shroud at higher flow rates.

Use of CFD to Improve Control Valve Effectiveness

2019 ◽  
Author(s):  
Alton Reich
Keyword(s):  
Flow Control ◽  
Control Valve ◽  
Steam Pressure ◽  
Steam Flow ◽  
Effective Control ◽  
Flow Control Valve ◽  
Flow Rates ◽  
Wide Range ◽  
Flow Through ◽  
Inlet Conditions

Abstract Control valves are used to adjust fluid flow rates in an extremely wide variety of applications. This paper discusses a steam flow control valve that is required to operate with a fairly wide range of inlet conditions (steam pressure) and provide effective control over a fairly wide range of steam flow rates. In this particular case a valve design was developed using “classical” methods — a combination of experience and hand calculations. The valve was tested and it did not provide adequate control over the flow for the application. The valve redesign effort used CFD to gain insight into the flow through the valve in order to evaluate control performance before the valve was fabricated and assembled. Several internal geometries were assessed and compared in order to identify two configurations that would meet the flow control requirements. These configurations were fabricated and tested and deemed to be adequate.

Analysis of a Novel Y-Y Micromixer for Mixing at a Wide Range of Reynolds Numbers

2016 ◽  
Vol 138 (9) ◽  
Author(s):  
Vladimir Viktorov ◽  
Carmen Visconte ◽  
Md Readul Mahmud
Keyword(s):  
Three Dimensional ◽  
Interfacial Area ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Change Of Direction ◽  
Analysis Technique ◽  
Wide Range ◽  
Passive Micromixer ◽  
In Series ◽  
Flow Through

A novel passive micromixer, denoted as the Y-Y mixer, based on split-and-recombine (SAR) principle is proposed and studied both experimentally and numerically over Reynolds numbers ranging from 1 to 100. Two species are supplied to a prototype via a Y inlet, and flow through four identical elements repeated in series; the width of the mixing channel varies from 0.4 to 0.6 mm, while depth is 0.4 mm. An image analysis technique was used to evaluate mixture homogeneity at four target areas along the mixer. Numerical simulations were found to be a useful support for observing the complex three-dimensional flow inside the channels. Comparison with a known mixer, the tear-drop one, based on the same SAR principle, was also performed, to have a point of reference for evaluating performances. A good agreement was found between numerical and experimental results. Over the examined range of Reynolds numbers Re, the Y-Y micromixer showed at its exit an almost flat mixing characteristic, with a mixing efficiency higher than 0.9; conversely, the tear-drop mixer showed a relevant decrease of efficiency at the midrange. The good performance of the Y-Y micromixer is due to the three-dimensional 90 deg change of direction that occurs in its channel geometry, which causes a fluid swirling already at the midrange of Reynolds numbers. Consequently, the fluid path is lengthened and the interfacial area of species is increased, compensating for the residence time reduction.

Interference in a three-dimensional array of jets

2015 ◽  
Vol 26 (5) ◽  
pp. 795-819
Author(s):  
P. E. WESTWOOD ◽  
F. T. SMITH
Keyword(s):  
Cross Sections ◽  
Flow Direction ◽  
Three Dimensional ◽  
Cross Flow ◽  
Longitudinal Vortex ◽  
Cross Sectional ◽  
Dimensional Array ◽  
Unsteady Jets ◽  
The Cross ◽  
Jet Cross Sections

The theoretical investigation here of a three-dimensional array of jets of fluid (air guns) and their interference is motivated by applications to the food sorting industry especially. Three-dimensional motion without symmetry is addressed for arbitrary jet cross-sections and incident velocity profiles. Asymptotic analysis based on the comparatively long axial length scale of the configuration leads to a reduced longitudinal vortex system providing a slender flow model for the complete array response. Analytical and numerical studies, along with comparisons and asymptotic limits or checks, are presented for various cross-sectional shapes of nozzle and velocity inputs. The influences of swirl and of unsteady jets are examined. Substantial cross-flows are found to occur due to the interference. The flow solution is non-periodic in the cross-plane even if the nozzle array itself is periodic. The analysis shows that in general the bulk of the three-dimensional motion can be described simply in a cross-plane problem but the induced flow in the cross-plane is sensitively controlled by edge effects and incident conditions, a feature which applies to any of the array configurations examined. Interference readily alters the cross-flow direction and misdirects the jets. Design considerations centre on target positioning and jet swirling.

Destructive Vibration of Trashracks due to Fluid-Structure Interaction

1975 ◽  
Vol 97 (4) ◽  
pp. 1359-1365 ◽  
Author(s):  
S. H. Crandall ◽  
S. Vigander ◽  
P. A. March
Keyword(s):  
Vortex Shedding ◽  
Storage System ◽  
Water Channel ◽  
Scale Model ◽  
Original Design ◽  
Cross Sectional ◽  
Flow Rates ◽  
Pumped Storage ◽  
Sectional Shape ◽  
Lock In

Trashracks in pumped storage systems with high flow rates can develop fatigue failures due to excessive vibration excited by the flow past the rods in the rack. An experimental study of trashrack vibration was made on a half-scale model of a prototype rack design for the TVA Raccoon Mountain pumped storage system. The natural frequencies and loss factors of the first dozen natural modes of the rack were determined in air before placing the rack in a water channel. Under normal flow rates the rack developed “locked-in” pure tone vibrations of sufficient amplitude to cause early fatigue failure. Unexpectedly, the frequency of the vibration was not close to the vortex-shedding frequency and the motion of the rods was not transverse to the flow. The “locked-in” modes were identified as modes in which the bending displacements of the rods were parallel to the flow. Further investigation showed that the excitation mechanism involved synchronization between the fluctuating drag involved in vortex shedding and the fore-and-aft motion of the rods in sharply resonant modes. Modifications of the original design were introduced to defeat the identified mechanism. In order to completely eliminate the “lock-in” phenomenon it was necessary to change the bar cross-sectional shape and to introduce additional damping into the rack structure. A half-scale model of the modified design was built and tested to verify the absence of destructive vibrations.

Cross-sectional shape effect of a diffuser micropump on flow rates

2011 ◽  
Vol 6 (8) ◽  
pp. 682 ◽  
Author(s):  
Chang-Ju Park ◽  
Byung-Phil Mun ◽  
Sung-Keun Yoo ◽  
Jong-Hyun Lee
Keyword(s):  
Shape Effect ◽  
Cross Sectional ◽  
Flow Rates ◽  
Sectional Shape

Simulation of Fluid Flow Through a Granular Bed

2006 ◽  
Author(s):  
Arezou Jafari ◽  
S. Mohammad Mousavi
Keyword(s):  
Stokes Equations ◽  
Numerical Study ◽  
Fluid Velocity ◽  
Three Dimensional ◽  
Packed Bed ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Wide Range ◽  
Duct Geometry ◽  
Flow Through

Numerical study of flow through random packing of non-overlapping spheres in a cylindrical geometry is investigated. Dimensionless pressure drop has been studied for a fluid through the porous media at moderate Reynolds numbers (based on pore permeability and interstitial fluid velocity), and numerical solution of Navier-Stokes equations in three dimensional porous packed bed illustrated in excellent agreement with those reported by Macdonald [1979] in the range of Reynolds number studied. The results compare to the previous work (Soleymani et al., 2002) show more accurate conclusion because the problem of channeling in a duct geometry. By injection of solute into the system, the dispersivity over a wide range of flow rate has been investigated. It is shown that the lateral fluid dispersion coefficients can be calculated by comparing the concentration profiles of solute obtained by numerical simulations and those derived analytically by solving the macroscopic dispersion equation for the present geometry.

scholarly journals A Comprehensive Observational Study of Graupel and Hail Terminal Velocity, Mass Flux, and Kinetic Energy

2018 ◽  
Vol 75 (11) ◽  
pp. 3861-3885 ◽  
Author(s):  
Andrew Heymsfield ◽  
Miklós Szakáll ◽  
Alexander Jost ◽  
Ian Giammanco ◽  
Robert Wright
Keyword(s):  
Reynolds Number ◽  
Kinetic Energy ◽  
Mass Flux ◽  
Three Dimensional ◽  
Acrylonitrile Butadiene Styrene ◽  
Terminal Velocity ◽  
Three Dimensions ◽  
Cross Sectional ◽  
Wide Range ◽  
3D Volume

Abstract This study uses novel approaches to estimate the fall characteristics of hail, covering a size range from about 0.5 to 7 cm, and the drag coefficients of lump and conical graupel. Three-dimensional (3D) volume scans of 60 hailstones of sizes from 2.5 to 6.7 cm were printed in three dimensions using acrylonitrile butadiene styrene (ABS) plastic, and their terminal velocities were measured in the Mainz, Germany, vertical wind tunnel. To simulate lump graupel, 40 of the hailstones were printed with maximum dimensions of about 0.2, 0.3, and 0.5 cm, and their terminal velocities were measured. Conical graupel, whose three dimensions (maximum dimension 0.1–1 cm) were estimated from an analytical representation and printed, and the terminal velocities of seven groups of particles were measured in the tunnel. From these experiments, with printed particle densities from 0.2 to 0.9 g cm−3, together with earlier observations, relationships between the drag coefficient and the Reynolds number and between the Reynolds number and the Best number were derived for a wide range of particle sizes and heights (pressures) in the atmosphere. This information, together with the combined total of more than 2800 hailstones for which the mass and the cross-sectional area were measured, has been used to develop size-dependent relationships for the terminal velocity, the mass flux, and the kinetic energy of realistic hailstones.

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