PAPER PHYSICS. PIV measurements of flow through forming fabrics

2012 ◽  
Vol 27 (4) ◽  
pp. 783-789 ◽  
Author(s):  
Haiya Peng ◽  
Sheldon I. Green
Keyword(s):  
Test Section ◽  
Single Phase ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Flow Speed ◽  
Flow Loop ◽  
Cfd Simulations ◽  
Piv Measurements ◽  
Velocity Deviation ◽  
Flow Through

Abstract The three-dimensional velocity field in the single phase approach flow to a multiple layer woven forming fabric was measured using PIV. The measurements were conducted on a scaled-up model of a forming fabric in a water/glycerin flow loop. Each strand on the paper side of the model forming fabric had a filament diameter ( d) of 1 5 mm, and the flow loop test section was 3 1 0 mm squared, permitting the measurement of detailed velocity distributions over multiple strands of the fabric. The flow speed in the loop test section was varied to achieve screen Reynolds numbers between 12 and 6 5 . PIV measurements showed that when the distance t o the paper side of the fabric changes from 0.25d to 1 . 5d, the normalized ZD, CMD and MD velocity deviation decreases from 1 9 .7% to 4 .2%, 1 5 . 3 % to 1 .9% and 1 4 . 5 % t o 2 . 3 %, respectively; the ratio between maximum and minimum ZD velocity decreases from 3 .3 to 1 .2 . These findings indicate that the flow non-uniformity caused by the fabric weave is confined to a short distance above the fabric. CFD simulations of the same flow were consistent with the PIV measurements.

Numerical investigation of near-wake characteristics of cavitating flow over a circular cylinder

2016 ◽  
Vol 790 ◽  
pp. 453-491 ◽  
Author(s):  
Aswin Gnanaskandan ◽  
Krishnan Mahesh
Keyword(s):  
Circular Cylinder ◽  
Single Phase ◽  
Three Dimensional ◽  
Low Frequency ◽  
Reynolds Numbers ◽  
Cavitating Flow ◽  
Cylinder Surface ◽  
Near Wake ◽  
Eddy Simulation ◽  
Wake Characteristics

A homogeneous mixture model is used to study cavitation over a circular cylinder at two different Reynolds numbers ($Re=200$ and 3900) and four different cavitation numbers (${\it\sigma}=2.0$, 1.0, 0.7 and 0.5). It is observed that the simulated cases fall into two different cavitation regimes: cyclic and transitional. Cavitation is seen to significantly influence the evolution of pressure, boundary layer and loads on the cylinder surface. The cavitated shear layer rolls up into vortices, which are then shed from the cylinder, similar to a single-phase flow. However, the Strouhal number corresponding to vortex shedding decreases as the flow cavitates, and vorticity dilatation is found to play an important role in this reduction. At lower cavitation numbers, the entire vapour cavity detaches from the cylinder, leaving the wake cavitation-free for a small period of time. This low-frequency cavity detachment is found to occur due to a propagating condensation front and is discussed in detail. The effect of initial void fraction is assessed. The speed of sound in the free stream is altered as a result and the associated changes in the wake characteristics are discussed in detail. Finally, a large-eddy simulation of cavitating flow at $Re=3900$ and ${\it\sigma}=1.0$ is studied and a higher mean cavity length is obtained when compared to the cavitating flow at $Re=200$ and ${\it\sigma}=1.0$. The wake characteristics are compared to the single-phase results at the same Reynolds number and it is observed that cavitation suppresses turbulence in the near wake and delays three-dimensional breakdown of the vortices.

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.

Numerical and Experimental Analysis of Single Phase Jet Interactions

2016 ◽  
Author(s):  
Freddy Hernandez-Alvarado ◽  
Randy Samaroo ◽  
Dinesh V. Kalaga ◽  
Taehun Lee ◽  
Sanjoy Banerjee ◽  
...  
Keyword(s):  
Single Phase ◽  
Tap Water ◽  
Liquid Jets ◽  
Reynolds Stresses ◽  
Cfd Simulations ◽  
Piv Measurements ◽  
Mass Transfer Processes ◽  
Image Velocimetry ◽  
Wide Range ◽  
Jet Interactions

Impinging liquid jets have many applications ranging from manufacturing processes to jet propulsion systems. In thermal applications, they are often used in atomization processes to cool the surfaces in extreme heat and mass transfer processes. In the present work, 2-D Particle Image Velocimetry (PIV) measurements have been performed to study the interaction of multiple vertical liquid jets in single-phase flow. A perforated Perspex plate with seven symmetrically placed holes was used to make the liquid jets of degassed tap water. From the PIV measurements, a wide range of liquid jet velocities were investigated, and hydrodynamic parameters such as the instantaneous velocity fields, axial (z) and radial (r) mean and RMS liquid velocities, vorticity, and in-plane Reynolds stresses have been derived. Transient 3-D CFD simulations have also been performed and compared with the experimental data. Good agreement has been found between the experimental and CFD simulations. Further, Reichardt’s hypothesis (1943) has also been examined to better understand the onset of instability for the single-phase multi jet flow.

Flow in a Mechanical Bileaflet Heart Valve at Laminar and Near-Peak Systole Flow Rates: CFD Simulations and Experiments

2005 ◽  
Vol 127 (5) ◽  
pp. 782-797 ◽  
Author(s):  
Liang Ge ◽  
Hwa-Liang Leo ◽  
Fotis Sotiropoulos ◽  
Ajit P. Yoganathan
Keyword(s):  
Heart Valve ◽  
Turbulence Modeling ◽  
Mechanical Heart Valve ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Cfd Simulations ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Flow Through

Time-accurate, fully 3D numerical simulations and particle image velocity laboratory experiments are carried out for flow through a fully open bileaflet mechanical heart valve under steady (nonpulsatile) inflow conditions. Flows at two different Reynolds numbers, one in the laminar regime and the other turbulent (near-peak systole flow rate), are investigated. A direct numerical simulation is carried out for the laminar flow case while the turbulent flow is investigated with two different unsteady statistical turbulence modeling approaches, unsteady Reynolds-averaged Navier-Stokes (URANS) and detached-eddy simulation (DES) approach. For both the laminar and turbulent cases the computed mean velocity profiles are in good overall agreement with the measurements. For the turbulent simulations, however, the comparisons with the measurements demonstrate clearly the superiority of the DES approach and underscore its potential as a powerful modeling tool of cardiovascular flows at physiological conditions. The study reveals numerous previously unknown features of the flow.

scholarly journals Turbulence Modeling in Three-Dimensional Stenosed Arterial Bifurcations

2006 ◽  
Vol 129 (1) ◽  
pp. 40-50 ◽  
Author(s):  
J. Banks ◽  
N. W. Bressloff
Keyword(s):  
Carotid Artery ◽  
Turbulence Modeling ◽  
Turbulent Viscosity ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Shape Variation ◽  
Severe Stenosis ◽  
Carotid Artery Bifurcation ◽  
Inflow Turbulence ◽  
Flow Through

Under normal healthy conditions, blood flow in the carotid artery bifurcation is laminar. However, in the presence of a stenosis, the flow can become turbulent at the higher Reynolds numbers during systole. There is growing consensus that the transitional k−ω model is the best suited Reynolds averaged turbulence model for such flows. Further confirmation of this opinion is presented here by a comparison with the RNG k−ϵ model for the flow through a straight, nonbifurcating tube. Unlike similar validation studies elsewhere, no assumptions are made about the inlet profile since the full length of the experimental tube is simulated. Additionally, variations in the inflow turbulence quantities are shown to have no noticeable affect on downstream turbulence intensity, turbulent viscosity, or velocity in the k−ϵ model, whereas the velocity profiles in the transitional k−ω model show some differences due to large variations in the downstream turbulence quantities. Following this validation study, the transitional k−ω model is applied in a three-dimensional parametrically defined computer model of the carotid artery bifurcation in which the sinus bulb is manipulated to produce mild, moderate, and severe stenosis. The parametric geometry definition facilitates a powerful means for investigating the effect of local shape variation while keeping the global shape fixed. While turbulence levels are generally low in all cases considered, the mild stenosis model produces higher levels of turbulent viscosity and this is linked to relatively high values of turbulent kinetic energy and low values of the specific dissipation rate. The severe stenosis model displays stronger recirculation in the flow field with higher values of vorticity, helicity, and negative wall shear stress. The mild and moderate stenosis configurations produce similar lower levels of vorticity and helicity.

scholarly journals Flow through pipe orifices at low Reynolds numbers

1930 ◽  
Vol 126 (801) ◽  
pp. 231-245 ◽  
Keyword(s):  
Turbulent Flow ◽  
Discharge Coefficient ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Orifice Diameter ◽  
Vortex System ◽  
Low Reynolds Numbers ◽  
Commercial Practice ◽  
Flow Through ◽  
Low Reynolds

Most of the experimental work in connection with the flow of fluids through diaphragm orifices in pipe lines has been directed to the establishment of the orifice as a flow meter, and has been carried out at the velocities of flow commonly encountered in commercial practice. As a result of such research the coefficients relating the volumetric discharge of incompressible fluids to the differential head across an orifice are well known over a large range of high Reynolds numbers. For a particular diameter ratio ( i. e., orifice diameter ÷ diameter of pipe line) the discharge coefficient is nearly constant under conditions of turbulent flow. Over the range from steady to turbulent flow, however, very appreciable variations occur in the value of the discharge coefficient, suggest­ing that the accompanying variations in the nature of the flow through and beyond the orifice will be no less marked. As regards the turbulent flow pattern, an investigation, in which the author collaborated, of the airflow downstream of a flat plate suggests that an orifice in a pipe will in general give rise to a vortex system, probably having some points of resemblance to the well-known Kármán street which is a feature of the two-dimensional flow past a bluff obstacle, but doubtless exhibiting interesting differences arising from the symmetrical and three-dimensional character of the flow through an orifice. At sufficiently low Reynolds numbers, on the other hand, perfect flow free from periodic vorticity will occur. The stages connecting these two extreme conditions present many points of interest not only as regards the nature of the vortex system downstream of the orifice and the conditions of flow covering its inception, but also as regards the accom­panying pressure-velocity relation during the transition.

Experimental Study of Three-Dimensional Laminar Wall Jets of Non-Newtonian Fluid

2009 ◽  
Author(s):  
Kofi K. Adane ◽  
Mark F. Tachie
Keyword(s):  
Newtonian Fluid ◽  
Open Channel ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Jet Flows ◽  
Wall Jet ◽  
Particle Image Velocimetry Technique ◽  
Piv Measurements ◽  
Image Velocimetry ◽  
Shear Thinning Fluid

A particle image velocimetry technique was employed to study three-dimensional laminar wall jet flows of a non-Newtonian shear-thinning fluid. The wall jet was created using a circular pipe of diameter 7 mm and flows into an open channel. The Reynolds numbers based on the pipe diameter and jet exit velocity were varied from 250 to 800. The PIV measurements were performed in various streamwise-transverse and streamwise-spanwise planes. From these measurements, the velocity profiles, jet growth rate and spread rates were obtained to study the characteristics of three-dimensional wall jet flows of a non-Newtonian fluid.

Laminar Flow through a Rectangular Horizontal Channel with Asymmetrical Contraction

2009 ◽  
Vol 15 ◽  
pp. 21-26
Author(s):  
O.A. Morales-Contreras ◽  
J.G. Barbosa-Saldaña ◽  
J.A. Jiménez-Bernal ◽  
Claudia del Carmen Gutiérrez Torres
Keyword(s):  
Numerical Simulation ◽  
Laminar Flow ◽  
Recirculation Zone ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Step Height ◽  
Axial Component ◽  
Parabolic Profile ◽  
Flow Through ◽  
Stream Direction

Numerical simulation for the three-dimensional laminar flow through a forward facing step channel was simulated by Fluent 6.3 code. Four Reynolds numbers and four step lengths were analyzed. The results showed that the length of the recirculation zone upstream the step depends on Reynolds number, as well as on the step height (h), while the height of the recirculation zone extends about 70% of the step height. In addition, it was found that the velocity profile in the stream direction at the channel exit presents a fully developed profile for the axial component. Nonetheless, the profile along the transversal direction does not have a parabolic profile, even for a length of 60h

Analysis of Swirl Flow by Tube Inserts for CFD Study

2015 ◽  
Author(s):  
Salem Bouhairie
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Single Phase ◽  
Tube Bundle ◽  
Reynolds Numbers ◽  
Swirl Flow ◽  
Twisted Tape ◽  
Cfd Simulations ◽  
Flow Length ◽  
Mechanical Methods

The petroleum and petrochemical industries continually seek mechanical methods to improve heat transfer in shell-and-tube heat exchangers. Tube bundle inserts are popular mechanical devices that help improve performance. The increase in the tubeside heat transfer coefficient by the insert allows for a decrease in required shellside flow length, assuming single tube pass. The flow length reduction allows for designing higher velocities and subsequent shellside shear rates, to help reduce crude oil fouling potential. This work presents some of HTRI’s ongoing experimental measurements and preliminary Computational Fluid Dynamics (CFD) simulations. CFD visualization of swirl flow dynamics and heat transfer inside the augmented tube provides insight on complex flow physics, which is misunderstood. Heat Transfer Research, Inc. (HTRI) collected experimental data for in-tube single-phase flow using twisted tape inserts in the Tubeside Single-Phase Unit (TSPU) situated in the Research and Technology Center (RTC). Our data will be used to calibrate ANSYS FLUENT CFD simulations of a tube with a twisted tape swirl insert. We first performed plain tube simulations and compared the heat transfer results with open literature measurements, for validation. We will modify the CFD tube model to have a swirl flow insert, and compare numerical results against open literature experimental data of diabatic single-phase swirl flow. In future, we will compute heat transfer (heating and cooling) and pressure drop for tube insert configurations at laminar and turbulent Reynolds numbers from 3000 to 500000. The range of tubeside Reynolds numbers required the use of the laminar, transition, and Realizable k-epsilon turbulence models with scalable wall functions. This study describes some of the mechanisms behind turbulent swirl flow augmentation inside a tube, as well as the limitations of conventional in-tube heat transfer correlations applied to swirl flow inserts.

Steady Inspiratory Flow in a Model Symmetric Bifurcation

1994 ◽  
Vol 116 (4) ◽  
pp. 488-496 ◽  
Author(s):  
Yao Zhao ◽  
Baruch B. Lieber
Keyword(s):  
Test Section ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Axial Position ◽  
Flow Loop ◽  
Low Velocity ◽  
Cross Sectional ◽  
Branching Angle ◽  
Head Pressure ◽  
Constant Head

Flow in a bifurcating tube system typifying a major bronchial bifurcation is studied experimentally with a two color, two velocity component laser Doppler anemometer. The flow loop is composed of a pumping station, flow stratifiers and a constant head pressure tank; it can accommodate steady, pulsatile or oscillatory flow. The test section is a symmetric bifurcation of constant cross sectional area and has a branching angle of 70 deg. The test section is a cast of clear silicon rubber in a plexiglass mold that was milled on a numerically controlled milling machine. The flow division ratio from the parent to daughter branches is about unity. Steady flow results that model the inspiratory phase at Reynolds numbers of 518, 1036 and 2089, corresponding to Dean numbers of 98, 196 and 395, show that in the bifurcation plane velocity profiles in the daughter branches are skewed toward the inner wall. In the transverse plane, “m” shaped velocity profiles are found with low velocity at the center. Secondary flow patterns, which are responsible for such phenomena, are first observed at the axial position where the flow begins to turn. Flow separation was not observed at any point in the bifurcation.

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