Project #4: Simulation of Fluid
Flow in the Screen-Bounded
Channel in a Fiber Separator
Lana Sneath and Sandra Hernandez
4th year - Biomedical Engineering
Faculty Mentor: Dr. Urmila Ghia
Department of Mechanical
and Materials Engineering
NSF Type 1 STEP Grant, Grant ID No.: DUE-0756921
Outline
• Motivation
• Introduction to Bauer
McNett Classifier
(separator)
• Problem Description
• Goals & Objectives
• Methodology
• Verification Case
• Porous Boundary
Model
• Future Work
1
Problem Background
• Toxicity of asbestos exposure varies with length of
asbestos fibers inhaled
• Further study of this effect requires large batches of
fibers classified by length
• The Bauer McNett Classifier (BMC) provides a
technology to length-separate fibers in large batches
Figure 1: Bauer McNett Classifier (BMC)
Figure 2: Schematic of BMC
2
Background – Bauer McNett
Classifier (BMC)
Open to
• Fiber separation occurs in
the deep narrow channel
with a wire screen on one
side wall
• Fibers align with local shear
stress vectors [1]
• For successful length-based
separation, the fibers must
be parallel to the screen
atmosphere
Wire
Screen
B
A
C
AL
= deep
1. Civelekogle-Scholey, G., Wayne Orr, A., Novak, I., Meister, J.-J.,
Schwartz, M. A., Mogilner, A. (2005), “Model of coupled transient
changes of Rac, Rho, adhesions and stress fibers alignment in
endothelial cells responding to shear stress”, Journal of Theoretical
Biology, vol 232, p569-585
open
channel
Figure 3: Top View of One BMC Tank
3
Background – Bauer McNett
Classifier (BMC)
Figure 4: Fibers
parallel to screen
Figure 5: Fibers
perpendicular to screen
Fibers length larger
than mesh opening
Fibers length
smaller than mesh
opening
Off-plane angle 0°
Off-plane angle 90°
4
Deep Open Channel Dimensions
General Dimensions:
• Length (x) = 0.217 m
• Height (y) = 0.2 m
• Width (z) = 0.02 m
• Aspect ratio = 10; Deep open
channel
Screen dimensions:
• Length (x) = 0.1662 m
• Height (y) = 0.1746 m
• Thickness (z) = 0.0009144 m
Figure 6: General Dimensions
Figure 7: Porous Model Dimensions
5
Goals and Objectives
Goal: Numerically study the fluid flow in a deep open
channel
Objectives:
a) Verify boundary conditions and variables of the porous
model
• Simplified porous plate problemas verification
case
b) Simulate and study the flow in the open channel of the
BMC apparatus, modeling the screen as a porous
boundary
c) Determine the orientation of shear stress vector on the
porous boundary
6
Methodology
•
Create channel geometry in CFD
software
•
Generate grid of discrete points
•
Determine the proper boundary
conditions to model the porous
boundary
Computational Grid
– Verification case: Laminar flow
over a porous plate
•
Enter boundary conditions into the
CFD software
•
Run simulation
•
Determine shear stress from flow
solutions
•
Interpret results
Figure 8: Porous Model Channel
Geometry in FLUENT
Table 1: Distribution of grid points and smallest
spacing near boundaries
7
Boundary Conditions
• u, v, w are the x, y, and
z components of
velocity, respectively
• Average Inlet Velocity=
0.25m/s
• Turbulent Flow
(Reynolds Number
>5000)
• Reynolds Stress Model
• Transient Simulation
Solid Wall Model
Porous Boundary Model
Free-Slip Wall, v=0, du/dy=0, dw/dy=0
No-Slip Wall, u = v = w = 0
Inlet, u = u(y,z), v = w =0
Outlet, pstat = 0
Porous-Jump, Permeability(K) = 9.6e10, Pressure-Jump
Coefficient(C2)=7610.7 1/m, screen
thickness = 9e-4 m; Values correspond
to a 16 mesh [5]
Figure 9: Boundary Conditions
8
Verification Case - Porous Plate
Objective
• Determine proper boundary conditions to
use in the Porous Boundary Model case
• Verify fluid flow behavior
• Observe how axial flow is inhibited by
the plate
Methodology:
• Create 2D geometry in Gambit
•
Calculate Reynolds number for
Laminar flow
•
Generate grid points
• Run simulations in FLUENT
•
Run 4 different cases: changing
the mesh boundary condition to
determine it’s effect
• Interpret results
Figure 10: Laminar Flow Across Porous Flat Plate
9
Verification Case - Boundary Conditions
Case #1:
All Solid Walls
(1 of 2)
Case #2:
Two Walls, One Pressure Outlet
10
Verification Case - Boundary Conditions
Case #3:
One Wall and Two Pressure Outlets
(2 of 2)
Case #4:
All Pressure Outlets
11
Verification Case - Velocity Magnitude Contours
Case #1:
Velocity Magnitude Contours for All Walls
Case #3:
Velocity Magnitude Contours for One Wall
and Two Pressure Outlets
Case #2:
Velocity Magnitude Contours for Two Walls
and One Pressure Outlet
Case #4:
Velocity Magnitude Contours for All Pressure Outlets
Conclusion:
• All cases show a boundary layer and flow crossing the porous plate
12
Verification Case Streamlines for Case #1: All Walls
13
Verification Case – Darcy’s Law
Model
Pressure Drop
Calculated Using
Darcy’s Law
Pressure Drop
Fluent
Percent Error
All Walls
3.48E-03
3.51781-03
1.19%
Two Walls and
One Pressure
Outlet
-3.73E-03
-3.679068E-03
1.25%
One Wall and Two
Pressure Outlets
2.54E-03
2.53E-03
0.32%
All Pressure Outlet
-8.593229E-03
-8.68129E-03
1.01%
Table 2: Pressure Drop Verification via Darcy’s Law
Conclusion:
• Hand calculations were equivalent to FLUENT’s values.
• Better understanding how FLUENT uses the porous-jump condition.
13
Porous Boundary Open Channel Velocity Magnitude Contours
Figure 11:
Isometric View of Axial Variation of
Velocity on Central Plane
Figure 12:
Front View of Axial Variation of Velocity
on Central Plane
14
Porous Boundary Open Channel - Shear Stress
Figure 13:
Axial Variation of Shear
Stress on the Back Wall
at y=0.1 z= 0
Figure 14:
Axial Variation of Shear
Stress on Screen at
y=0.1 z= 0.02
Figure 15:
Axial Variation of
Velocity at Line
y=0.1, z=0.01
15
Future Work
• Continue running the porous boundary open
channel model until the fluid flow solution has
been calculated for at least 3 minutes to
achieve a steady state solution
• Investigate reasoning behind the zero shear
stress at the porous boundary
• Compare verification case results for pressure
drop calculations to literature
• Interpret results further
16
Acknowledgements
• Dr. Ghia for being an excellent faculty mentor and taking
the time to make sure we fully understood the concepts
behind our research.
• Graduate Students Prahit, Chandrima, Deepak, Nikhil,
and Santosh for taking time out of their schedule to
teach us the software and help us with any problems we
encountered.
• Funding for this research was provided by the NSF
CEAS AY REU Program, Part of NSF Type 1 STEP
Grant, Grant ID No.: DUE-0756921
17
Appendix: Porous Plate Calculation
• Darcy’s Law pressure drop calculations:
18