1. Workshop 6 Modeling of Catalytic Convertor
Introductory FLUENT Training

2. Ceramic Monolith Substrate
Introduction
A workshop to demonstrate how to model porous media in FLUENT
Workshop models a catalytic convertor. Nitrogen flows in though inlet with an uniform velocity 22.6 m/s, passes through a ceramic monolith substrate with square shaped channels, and then exits through the outlet.
Substrate is impermeable in Y and Z directions, which is modeled by specifying loss coefficients 3 order higher than in X direction
Ceramic Monolith Substrate
I’d like to remind everyone that some matters that will be discussed during this presentation may constitute forward-looking statements that involve risks and uncertainties, which could cause actual results to differ from those projected.
In addition, I would also like to mention that we will not be able to discuss or answer any questions regarding previously provided guidance, as our Company policy is that we only comment on company guidance in a public forum.
Inlet
Outlet

3. Starting Fluent in Workbench
Open the Workbench (Start > Programs > ANSYS 12.0 > ANSYS Workbench)
Drag FLUENT into the project schematic
Change the name to Catalytic
Double click on Setup
Choose 3D and Double Precision under Options and retain the other default settings

4. Import Mesh
This starts a new Fluent session and the first step is to import the mesh that has already been created:
Under the File menu select Import> Mesh
Select the file catalytic_converter_125k.msh.gz and click OK to import the mesh
After reading the mesh, check the grid using Mesh>Check option
or by using Check under Problem Setup>General

5. Setting up the Models
Select Pressure Based, Steady state solver Problem Setup>General>Solver
Specify Turbulence model
Problem Setup > Models > Viscous
Double click and select k-epsilon (2 eqn) under Model and Realizable under k-epsilon model and retain the default settings for the other parameters
Make sure that the Energy Equation is disabled
Problem Setup > Models> Energy

6. Materials Define the materials. Problem Setup > Materials
Click on air to open Create/Edit Materials panel
Click on FLUENT Database…> Select nitrogen(n2) from the list > Copy
Click on Change/Create

7. Fluid Zone Conditions
Under Problem Setup >Cell Zone >Double click on part-in under Zone
Select Material Name : nitrogen
Default values for other settings
Click to OK
Similarly, visit to part-out Zone and
select the same settings as above

8. Fluid Zone Conditions (2)
Under Problem Setup ->Cell Zone ->Double click on part-catalyst under Zone
Select Material Name : nitrogen
Select and click on Porous Zone
Under Direction-1 Vector, specify as: 1, 0, 0
Under Direction-2 Vector, specify as: 0, 1, 0
Specify as per GUI under Viscous Resistance and Inertia Resistance
Default values under Power law Model and Porosity

9. Operating Conditions
Under Problem Setup >Cell Zone Conditions (operating conditions are also in BC panel)
Click on Operating Conditions… and set the Operating Pressure (Pascal) to pascal

10. Boundary Conditions Under Problem Setup > Boundary Conditions
Select inlet under Zone and choose velocity-inlet from the drop down menu under Type
Now double click on inlet under Zone
Input all the parameters in Momentum tab as shown below

11. Boundary Conditions (2)
Under Problem Setup > Boundary Conditions
Select outlet under Zone and choose pressure-outlet from the drop down menu under Type
Now double click on outlet under Zone
Input all the parameters in Momentum tab as shown below

12. Boundary Conditions (3)
Under Problem Setup > Boundary Conditions
Wall type boundary condition for the Zone: wall-part-catalyst, wall-part- in and wall-part-out
Interior type of boundary condition for the rest

13. Solution Methods Under Problem Setup > Solution Methods
Select Coupled under Pressure-Velocity Coupling
Select Green-Gauss Node Based under Gradient
Default under other options

14. Solution Controls Under Problem Setup > Solution Controls
Use default settings

15. Residual Monitors Residual Monitoring Solution > Monitors
Double click on Residuals (By default it is on)
Enable Plot under Options.
Specify Absolute Criteria for continuity: 1e-4

16. Surface Monitors Surface Monitors
Monitor points are used to monitor quantities of interest during the solution. They should be used to help judge convergence. In this case you will monitor the Mass Flow Rate at outlet and Static Pressure at inlet.
Solution > Monitors > Surface Monitors

17. Initialization
Before starting the calculations we must initialize the flow field in the entire domain
Solution > Monitors > Solution Initialization
Initializing the flow field with near steady state conditions will result in faster convergence
Select Compute from: inlet
Click on Initialize to initialize the solution

18. First Order Solution
The solution process can be started in the following manner
Solution >Run Calculation
Enter 100 for Number of Iterations and click on Calculate
During the iteration process, the residuals and monitor plots will be shown in different windows. You will see that both monitors become flat at 100 iterations. However, this is a solution of first order discretization scheme. To get an accurate solution, we will use higher order discretization scheme for pressure and momentum equations and run further.

19. Higher Order Solution
Under Solution>Solution Methods setup the parameters as shown below
The solution process can be started in the following manner
Solution >Run Calculation
Enter 100 for Number of Iterations and click on Calculate

20. Convergence history of the solution
Convergence history of the solution can be found from the plots
Scaled Residuals
Convergence history of
Mass Flow Rate on outlet
Convergence history of
Static Pressure on inlet

21. Write Case/Data File
You can now save the project and proceed to write a case file for the solver:
To save the project, go to Project Page
File>Save as
To write the case/data files, go to FLUENT session
File>Export>Case and Data..
Case/Data File: catalytic_converter_second.cas.gz

22. Post Processing To Draw Contours of Static Pressure on walls
Display > Graphics and Animations
Double Click on Contours, a new window will pop up
Select Pressure under Contours of and Static Pressure below that
Select all walls under Surfaces

23. Post Processing
To get the pressure drop between inlet to outlet boundaries using the porous media model
Reports > Surface Integrals
Select as per the GUI and click to Compute
You will get the information below
Hence, the pressure drop is around 734 pascal

24. Post Processing
You can postprocess any results using the FLUENT postprocessing tools and/or CFD-Post.