scholarly journals Viscous flow through microfabricated axisymmetric contraction/expansion geometries

2020 ◽  
Vol 61 (9) ◽  
Author(s):  
Francisco Pimenta ◽  
Kazumi Toda-Peters ◽  
Amy Q. Shen ◽  
Manuel A. Alves ◽  
Simon J. Haward
Keyword(s):  
Creeping Flow ◽  
Sudden Expansion ◽  
Viscoelastic Flows ◽  
Micro Particle Image Velocimetry ◽  
Numerical Predictions ◽  
Deformation Dynamics ◽  
Radial Dimension ◽  
Microfabrication Technique ◽  
Hyperbolic Contraction ◽  
Laser Induced Etching

Abstract We employ a state-of-the-art microfabrication technique (selective laser-induced etching) to fabricate a set of axisymmetric microfluidic geometries featuring a 4:1 contraction followed by a 1:4 downstream expansion in the radial dimension. Three devices are fabricated: the first has a sudden contraction followed by a sudden expansion, the second features hyperbolic contraction and expansion profiles, and the third has a numerically optimized contraction/expansion profile intended to provide a constant extensional/compressional rate along the axis. We use micro-particle image velocimetry to study the creeping flow of a Newtonian fluid through the three devices and we compare the obtained velocity profiles with finite-volume numerical predictions, with good agreement. This work demonstrates the capability of this new microfabrication technique for producing accurate non-planar microfluidic geometries with complex shapes and with sufficient clarity for optical probes. The axisymmetric microfluidic geometries examined have potential to be used for the study of the extensional properties and non-linear dynamics of viscoelastic flows, and to investigate the transport and deformation dynamics of bubbles, drops, cells, and fibers. Graphic abstract

Laser Velocimeter Measurements in Highly Turbulent Recirculating Flows

1984 ◽  
Vol 106 (2) ◽  
pp. 173-180 ◽  
Author(s):  
W. H. Stevenson ◽  
H. D. Thompson ◽  
R. R. Craig
Keyword(s):  
Turbulent Flows ◽  
Turbulence Model ◽  
Quantitative Description ◽  
Sudden Expansion ◽  
Laser Doppler Velocimeter ◽  
Bias Error ◽  
Mean Velocity ◽  
One Dimensional ◽  
Numerical Predictions ◽  
Velocity Bias

This paper presents the results of an extensive study of subsonic separated flows using a laser Doppler velocimeter. Both a rectangular rearward facing step and cylindrical (axisymmetric) sudden expansion geometry were studied. The basic objectives were to resolve the question of whether a velocity bias error does, in fact, occur in LDV measurements in highly turbulent flows of this type and, if so, how it may be eliminated; map the velocity field (mean velocity, turbulence intensity, Reynolds stress, etc.) including the entire recirculation zone; and compare experimental results with numerical predictions based on the k-ε turbulence model. Measurements were carried out using a one-dimensional LDV operating in forward scatter with signal processing by means of a commercial counter-type processor. Results obtained show that velocity bias does occur in turbulent flows and that it can be overcome by proper data acquisition procedures. The results also indicate that the important mean velocity and turbulence quantities can be obtained with reasonable accuracy using a one-dimensional LDV system. Although the k-ε turbulence model provides a good qualitative picture of the flow field, it does not yield a completely adequate quantitative description. Results obtained here illustrate the discrepancies to be expected and provide a basis for further model development.

Comparison of Lagrangian and Eulerian Simulations of Slurry Flows in a Sudden Expansion

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
P. Frawley ◽  
A. P. O’Mahony ◽  
M. Geron
Keyword(s):  
Impact Angle ◽  
Measured Data ◽  
Sudden Expansion ◽  
Dispersed Phase ◽  
Reattachment Point ◽  
Eulerian Model ◽  
Two Phase ◽  
Technical Literature ◽  
Numerical Predictions ◽  
Erosion Profiles

From a review of technical literature, it was not apparent if the Lagrangian or the Eulerian dispersed phase modeling approach was more valid to simulate dilute erosive slurry flow. In this study, both modeling approaches were employed and a comparative analysis of performances and accuracy between the two models was carried out. Due to an impossibility to define, for the Eulerian model already implemented in FLUENT, a set of boundary conditions consistent with the Lagrangian impulsive equations, an Eulerian dispersed phase model was integrated in the FLUENT code using subroutines and user-defined scalar equations. Numerical predictions obtained from the two different approaches for two-phase flow in a sudden expansion were compared with the measured data. Excellent agreement was attained between the predicted and observed fluid and particle velocity in the axial direction and for the kinetic energy. Erosion profiles in a sudden expansion computed using the Lagrangian scheme yielded good qualitative agreement with measured data and predicted a maximum impact angle of 29 deg at the fluid reattachment point. The Eulerian model was adversely affected by the reattachment of the fluid phase to the wall and the simulated erosion profiles were not in agreement with the Lagrangian or measured data. Furthermore, the Eulerian model under-predicted the Lagrangian impact angle at all locations except the reattachment point.

Radial and Axial Turbulent Flow Measurements With an LDV in an Axisymmetric Sudden Expansion Air Flow

1988 ◽  
Vol 110 (4) ◽  
pp. 367-372 ◽  
Author(s):  
R. P. Durrett ◽  
W. H. Stevenson ◽  
H. D. Thompson
Keyword(s):  
Radial Velocity ◽  
Air Flow ◽  
Sudden Expansion ◽  
Radial Velocity Component ◽  
Flow Measurements ◽  
Numerical Predictions ◽  
Index Matching ◽  
Cylindrical Tubes ◽  
Refractive Index Matching ◽  
Matching Techniques

Radial velocity component measurements in cylindrical tubes have been difficult to make because of optical aberrations introduced by the curved tube wall. This is particularly troublesome in gas flows where refractive index matching techniques cannot be employed. The present investigation utilized a specially designed correction lens system to overcome this problem. As a result it was possible to map the axial and radial velocity behavior in detail for the air flow downstream of a sudden expansion in a cylindrical duct. Quantities measured and derived included mean velocities, turbulence intensities, turbulent kinetic energy and Reynolds stress. The weak secondary recirculation zone existing just below the sudden expansion was clearly identified and mapped. Where possible the measurements were compared with numerical predictions based on a k-ε model.

Limitations of the Boundary-Layer Equations for Predicting Laminar Symmetric Sudden Expansion Flows

1986 ◽  
Vol 108 (2) ◽  
pp. 208-213 ◽  
Author(s):  
J. P. Lewis ◽  
R. H. Pletcher
Keyword(s):  
Boundary Layer ◽  
Initial Conditions ◽  
Boundary Layer Equation ◽  
Reynolds Numbers ◽  
Equation Model ◽  
Sudden Expansion ◽  
Boundary Layer Equations ◽  
Flow Parameters ◽  
Numerical Predictions ◽  
Global Iteration

A finite-difference solution scheme is used to study the limitations and capabilities of the boundary-layer equation model for flow through abrupt, symmetric expansions. Solutions of the boundary-layer equations are compared with previous numerical predictions and experimental measurements. Some flow parameters are not well predicted for Reynolds numbers below 200. Global iteration over the flow field to include upstream effects does not significantly influence the predictions. Axisymmetric and two-dimensional flows are investigated. The effect of initial conditions is discussed

The plane Symmetric sudden-expansion flow at low Reynolds numbers

1993 ◽  
Vol 248 ◽  
pp. 567-581 ◽  
Author(s):  
F. Durst ◽  
J. C. F. Pereira ◽  
C. Tropea
Keyword(s):  
Maximum Flow ◽  
Reynolds Numbers ◽  
Sudden Expansion ◽  
Channel Height ◽  
Low Reynolds Numbers ◽  
Plane Symmetric ◽  
Numerical Predictions ◽  
Flow Through ◽  
Volume Method ◽  
Good Agreement

Detailed velocity measurements and numerical predictions are presented for the flow through a plane nominally two-dimensional duct with a Symmetric sudden expansion of area ratio 1:2. Both the experiments and the predictions confirm a symmetry-breaking bifurcation of the flow leading to one long and one short Separation zone for channel Reynolds numbers above 125, based on the upstream channel height and the maximum flow velocity upstream. With increasing Reynolds numbers above this value, the short separated region remains approximately constant in length whereas the long region increases in length.The experimental data were obtained using a one-component laser-Doppler anemometer at many Reynolds number values, with more extensive measurements being performed for the three Reynolds numbers 70, 300 and 610. Predictions were made using a finite volume method and an explicit quadratic Leith type of temporal discretization. In general, good agreement was found between measured and predicted velocity profiles for all Reynolds numbers investigated.

scholarly journals Turbulent Flow in a Micro-Channel

2006 ◽  
Author(s):  
Tomasz A. Kowalewski ◽  
Slawomir Blonski ◽  
Piotr M. Korczyk
Keyword(s):  
Experimental Data ◽  
Energy Dissipation ◽  
Turbulent Flow ◽  
High Speed ◽  
Pure Water ◽  
Nano Particles ◽  
Flow Measurements ◽  
Micro Particle Image Velocimetry ◽  
Micro Piv ◽  
Numerical Predictions

Turbulent flow of water in a narrow gap of an emulsifier is investigated experimentally using micro-PIV (micro Particle Image Velocimetry) technique and compared with numerical predictions performed using the commercial code Fluent. The purpose of the investigations is to develop a procedure for well-controlled generation of mono-disperse suspension of micro droplets. These droplets will form a matrix for collection of nano-particles into well-structured configuration [1]. The micro-flow measurements are based on epi-fluorescence illumination and high-speed imaging. The experimental data are compared with the numerical results obtained using both turbulent and laminar flow models. It was found that, due to small channel dimensions and very small flow development length, the turbulent energy dissipation takes place mainly in the gap and shortly behind it. Very low amount of oil-phase fraction in investigated emulsions justifies us to use mean energy dissipation estimated for pure water to predict mean diameter of oil droplets. These predictions are validated using experimental data for the emulsion.

Three component velocity measurements of an isothermal confined swirling flow

1997 ◽  
Vol 211 (2) ◽  
pp. 113-122 ◽  
Author(s):  
S A Ahmed
Keyword(s):  
Swirling Flow ◽  
Sudden Expansion ◽  
Recirculation Region ◽  
Laser Doppler Velocimeter ◽  
Velocity Measurements ◽  
Radial Velocity Component ◽  
Numerical Predictions ◽  
Velocity Gradients ◽  
Component Velocity ◽  
High Turbulence

A two-component fibre-optic laser Doppler velocimeter (LDV) system has been employed to measure the flowfield characteristics of a confined, isothermal strongly swirling flow in a combustor model. The primary objectives are to understand such complex flowfields and to provide complete benchmark data for comparisons with numerical predictions based on practical models for turbulent swirling flows, and thereby guide the development of such models. For this confined strongly swirling flow, the measurements show the radial velocity component (close to the swirler exit) to be of the same order as the axial and swirl components. Comprehensive and detailed data show a large central recirculation region close to the dump plane which extends beyond the last measurement station. High velocity gradients and high turbulence activities are common for this type of flow and the current set of data confirms these previous findings. Generally speaking, most of the mixing takes place in the shear layer between the annular swirling jet and the corner recirculation region due to the sudden expansion.

Sign in / Sign up

Export Citation Format

Share Document