scholarly journals Computational Predictions for Boger Fluids and Circular Contraction Flow under Various Aspect Ratios

Fluids ◽  
2020 ◽  
Vol 5 (2) ◽  
pp. 85 ◽  
Author(s):  
J. Esteban López-Aguilar ◽  
Hamid R. Tamaddon-Jahromi
Keyword(s):  
Stress Response ◽  
Normal Stress ◽  
Contraction Flow ◽  
Pressure Drops ◽  
Aspect Ratios ◽  
Model Variant ◽  
Evolution Characteristics ◽  
Contraction Ratio ◽  
Boger Fluids ◽  
Experimental Findings

This work puts forward a modeling study contrasted against experimental, with focus on abrupt circular contraction flow of two highly-elastic constant shear-viscosity Boger fluids, i.e., a polyacrylamide dissolved in corn-syrup PAA/CS (Fluid-1) and a polyisobutylene dissolved in polybutene PIB/PB (Fluid-2), in various contraction-ratio geometries. Moreover, this work goes hand-in-hand with the counterpart matching of experimental pressure-drops observed in such 4:1 and 8:1 aspect-ratio contraction flows, as described experimentally in the literature. In this study, the experimental findings, for Boger fluids with severe strain-hardening features, reveal significant vortex-evolution characteristics, correlated with enhanced pressure-drop phasing and normal-stress response in the corner region. It is shown how such behavior may be replicated through simulation and the rheological dependencies that are necessary to bring this about. Predictive solutions with an advanced hybrid finite-element/volume (fe/fv) algorithm are able to elucidate the rheological properties (extensional viscosity and normal-stress response) that rule such vortex-enhancement evolution. This is accomplished by employing the novel swanINNFM(q) family of fluids, through the swIM model-variant, with its strong and efficient control on elongational properties.

scholarly journals On the use of continuous spectrum and discrete-mode differential models to predict contraction-flow pressure drops for Boger fluids

2017 ◽  
Vol 29 (12) ◽  
pp. 121613 ◽  
Author(s):  
J. E. López-Aguilar ◽  
M. F. Webster ◽  
H. R. Tamaddon-Jahromi ◽  
O. Manero ◽  
D. M. Binding ◽  
...  
Keyword(s):  
Continuous Spectrum ◽  
Contraction Flow ◽  
Pressure Drops ◽  
Discrete Mode ◽  
Boger Fluids ◽  
Flow Pressure

scholarly journals Numerical vs experimental pressure drops for Boger fluids in sharp-corner contraction flow

2016 ◽  
Vol 28 (10) ◽  
pp. 103104 ◽  
Author(s):  
J. E. López-Aguilar ◽  
H. R. Tamaddon-Jahromi ◽  
M. F. Webster ◽  
K. Walters
Keyword(s):  
Sharp Corner ◽  
Contraction Flow ◽  
Pressure Drops ◽  
Boger Fluids ◽  
Experimental Pressure

Hydrodynamic Entrance Lengths for Incompressible Laminar Flow in Rectangular Ducts

1960 ◽  
Vol 27 (3) ◽  
pp. 403-409 ◽  
Author(s):  
L. S. Han
Keyword(s):  
Rectangular Channel ◽  
Theoretical Data ◽  
Mathematical Expression ◽  
Smooth Transition ◽  
Navier Stokes ◽  
Entrance Length ◽  
Entire Region ◽  
Navier Stokes Equation ◽  
Pressure Drops ◽  
Aspect Ratios

The problem of determining the hydrodynamic entrance length in a rectangular channel is solved by the method of linearizing the Navier-Stokes equation. The resulting equation is regarded as an equation to generate a mathematical expression for the axial velocity in the entire region, making smooth transition from a uniform profile to the fully developed one. From this expression, the entrance length, defined as where 99 per cent of the fully developed center-line velocity is attained, is calculated for channels of six aspect ratios. The pressure drops are also calculated and presented herein. A comparison is made with the limited amount of experimental and theoretical data.

scholarly journals The Café Wall Illusion: Local and Global Perception from Multiple Scales to Multiscale

2017 ◽  
Vol 2017 ◽  
pp. 1-22 ◽  
Author(s):  
Nasim Nematzadeh ◽  
David M. W. Powers
Keyword(s):  
Peripheral Vision ◽  
Multiple Scales ◽  
Human Perception ◽  
Optical Illusions ◽  
Black And White ◽  
Difference Of Gaussians ◽  
Aspect Ratios ◽  
Geometrical Illusions ◽  
Model Variant ◽  
High Level

Geometrical illusions are a subclass of optical illusions in which the geometrical characteristics of patterns in particular orientations and angles are distorted and misperceived as a result of low-to-high-level retinal/cortical processing. Modelling the detection of tilt in these illusions, and its strength, is a challenging task and leads to the development of techniques that explain important features of human perception. We present here a predictive and quantitative approach for modelling foveal and peripheral vision for the induced tilt in the Café Wall illusion, in which parallel mortar lines between shifted rows of black and white tiles appear to converge and diverge. Difference of Gaussians is used to define a bioderived filtering model for the responses of retinal simple cells to the stimulus, while an analytical processing pipeline is developed to quantify the angle of tilt in the model and develop confidence intervals around them. Several sampling sizes and aspect ratios are explored to model variant foveal views, and a variety of pattern configurations are tested to model variant Gestalt views. The analysis of our model across this range of test configurations presents a precisely quantified comparison contrasting local tilt detection in the foveal sample sets with pattern-wide Gestalt tilt.

Increasing the stability of high contraction ratio flow of Boger fluids by pre-deformation

2013 ◽  
Vol 196 ◽  
pp. 27-35 ◽  
Author(s):  
Ashwin K. Sankaran ◽  
Douwe A. Dros ◽  
Hans J. Meerman ◽  
Stephen J. Picken ◽  
Michiel T. Kreutzer
Keyword(s):  
Contraction Ratio ◽  
Boger Fluids ◽  
The Stability

Normal stress differences in suspensions of rigid  fibres

2014 ◽  
Vol 758 ◽  
pp. 486-507 ◽  
Author(s):  
Braden Snook ◽  
Levi M. Davidson ◽  
Jason E. Butler ◽  
Olivier Pouliquen ◽  
Élisabeth Guazzelli
Keyword(s):  
Normal Stress ◽  
Fibre Length ◽  
Normal Stress Difference ◽  
Contact Forces ◽  
Stress Difference ◽  
Normal Stresses ◽  
First Normal Stress Difference ◽  
Second Normal Stress Difference ◽  
Aspect Ratios ◽  
Normal Stress Differences

AbstractMeasurements of normal stress differences are reported for suspensions of rigid, non-Brownian fibres for concentrations of $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}nL^2d=1.5\text {--}3$ and aspect ratios of $L/d=11\text {--}32$, where $n$ is the number of fibres per unit volume, $L$ is the fibre length and $d$ is the diameter. The first and second normal stress differences are determined experimentally from measuring the deformation in the free surface in a tilted trough and in a Weissenberg rheometer. Simulations are performed as well, and the hydrodynamic and contact contributions to the normal stresses are calculated. The experiments and simulations indicate that the second normal stress difference is negative and that its magnitude increases as the concentration is raised and the aspect ratio is lowered. The first normal stress difference is positive and its magnitude is approximately twice that of the second normal stress difference. Simulation results indicate that, for the concentrations and aspect ratios studied, contact forces between fibres form the dominant contribution to the normal stress differences.

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