Simulation of Fluid Flow in the Deep Open Channel of the BMC Apparatus
Lana Sneath and Sandra Hernandez
Biomedical Engineering Class of 2015, University of Cincinnati
Faculty Mentor: Dr. Urmila Ghia, Department of Mechanical and Material Engineering
Introduction
Boundary Conditions: Calculating K and C2
Asbestos toxicity has been shown to vary with fiber length. To conduct
larger scale studies on this effect, a fiber separator capable of filtering
large batches of fibers based on length is needed. Fibers align with
local shear stress vectors, therefore fibers will be filtered when the
shear stress is parallel to the wire-mesh. This study evaluates the
effectiveness of the Bauer McNett Classifier (BMC) as a fiber separator.
To model a porous boundary in FLUENT, the values of the permeability
(k), pressure-jump coefficient (C2), and the thickness of the porous
boundary need to first be determined.
Results: Porous Boundary Model
= Deep Open
Channel
Methods and Materials
Results: Solid Side Walls Model
Materials:
Computational Fluid Dynamic (CFD) tools FLUENT and Gambit
Methodology:
a) Define channel geometry
b) Set up channel geometry in Gambit and generate a computational
grid
c) Enter boundary conditions and obtain flow solutions
i. Verification Case – Flow over porous plate
ii. Porous Boundary Model
d) Compute shear stress on flow solutions
Geometry and Boundary Conditions
Total Shear Stress – Solid Wall Model
Shear Stress Magnitude
(Pascals)
Goal: Numerically study the fluid flow in a deep open channel
Objectives :
a)Determine boundary conditions and geometry
• Porous plate verification case
b) Simulate the open channel in FLUENT
• Model the screen as a porous boundary
c) Determine the orientation of shear stress vectors on the screen
2
1,8
1,6
1,4
1,2
1
0,8
0,6
0,4
0,2
0
14
12
10
8
6
4
2
0
0
0,1
Total
Stress
Off Plane
Shear
Stress
Angle
0,2
Y
Z
180 45
∆Ymin
0.000
05
0,05
0,10
0,16
0,21
X-Position (m)
• The lower velocity in the channel at porous-jump boundary is due to
the addition of the screen and increased area.
• The shear stress distribution on the z= 0m wall in the porousboundary model is similar to the solid wall case.
X-Position (m)
Figure 5: Axial variation of shear stress and off plane angle (secondary yaxis) along the Z-Wall; line at y= 0.1 m (mid-plane), z= 0.0 m
• These findings indicate that the total shear stress value is greatest at
the inlet, and quickly drops down as the x-position increases.
• In the solid-wall model, the highest out-plane angle where the screen
lies in the actual BMC channel is 8 degrees, which is primarily
tangential to the wall.
Discussion
The results obtained are only for 0.5 seconds of the fluid flow, whereas
the time period for the flow to travel across the channel is 0.87 seconds.
Hence, it is expected that the results will be significantly different once
the simulation is complete.
Conclusions:
• Off plane angle of the solid-wall model is significant and shows that
fibers will primarily align parallel to the screen
• These findings aid in understanding the chances in fluid flow behavior
with the addition of the porous-jump boundary condition
Free-Slip Wall, v=0, du/dy=0, dw/dy=0
No-Slip Wall, u = v = w = 0
Acknowledgements
Inlet, u = u(y,z), v = w =0
We would like to thank Dr. Ghia for being an excellent faculty mentor
Thank you to our sponsor, the National Science Foundation , Grant ID No.: DUE-0756921
Porous Boundary Model
Figure 4. Boundary Conditions
Total X
Points
40500 50
0
1,8
1,6
1,4
1,2
1
0,8
0,6
0,4
0,2
0
0,00
Future Work
• Further research shear stress across the porous-boundary condition
• Continue simulation until the fluid flow solution completes 4 to 5
cycles through the channel (at least 3 minutes)
Solid Wall Model
Table 1. Distribution of grid points and
smallest spacing near boundaries
Total Shear Stress - Porous-Boundary Model
Figure 8: Axial variation in shear stress on solid wall at y-0.1m, z=0.02m
Results: Porous Boundary Verification Case
Figure 3. Channel Geometry in Gambit
Figure 7: Contour plot of the X-velocity (Axial velocity) component.
Shear Stress Magnitude
(Pascals)
Figure 2. Top view of elliptical tank in the BMC
Off Plane Angle (degrees)
Figure 1. Side view of BMC apparatus
For a 16 mesh, wire diameter = 0.0004572. Screen thickness is 2d,
equal to 0.0009144. F and K/d^2 are standard coefficients for a 16
mesh [5]
These values are entered into FLUENT to analyze the flow in the
porous boundary model.
∆Zmin
Outlet, pstat = 0
0.000
7
Porous-Jump, K = 9.6e-10, C2=7610.7
1/m, screen thickness = 9e-4 m;
Values correspond to 16 a mesh [5]
References
Figure 6: Contour plot of the X-velocity (Axial velocity) component.
• Boundary layer forms around porous plate
• Cross-over of flow across the porous plate
• Further understood porous-boundary condition
1. Jana, C. (2011), “Numerical Study of Three-Dimensional Flow Through a Deep Open Channel-Including a WireMesh Segment on One Side Wall.” M.S. Mechanical Engineering Thesis, University of Cincinnati.
2. White, F. M. (2003) “ Fluid Mechanics”, McGraw-Hill, 5th Edition.
3. Fluent 6.3 User’s Guide.
4. Gambit 2.4 User’s Guide.
5. Tamayol, A., Wong, K. W., Bahrami, M. (2012) “Effects of microstructure on flow properties of fibrous porous media
at moderate Reynolds number”, American Physical Society, Physical Review E 85.