cfx 5.7 catalytic converter simulation workshop 11 ansys cfx 5.7

CFX 5.7

Catalytic Converter Simulation

Workshop 11

ANSYS CFX 5.7

Workshop

CFX v5.7

October 1, 2004Inventory #002157

WS11-2© 2004 ANSYS, Inc. CFX 5.7

Introduction

The catalyst material in the center region is a honeycomb structure upon which reactions

take place

The honeycomb structure is too small to resolve in mesh; it is modeled with a flow

resistance instead.

Focus: use of CFX to set up a flow simulation in ANSYS Workbench (this workshop is based

on imported meshes; second focuses on CFX-Mesh)

Note: this is preview version!!!

Steps:

Preprocess in CFX-Pre, solve in CFX-Solver, and post-process in CFX-Post

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CFX v5.7



Catalytic Converter Geometry

First start the ANSYS Workbench...

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CFX v5.7



Starting the CFX in Workbench

Common starting point for

all ANSYS software

New Project – save

explicitly to start!

Select New Simulation

Advanced CFD tab will

open

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Starting the CFX-5 Preprocessor

Simulation files have *.cfx

extension

Create converter.cfx in your

working directory

Click on Save to save the

simulation file

Copy the following mesh files to your working directory

CatConvHousing.msh & CatConvMesh.gtm

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Importing the Hex Mesh

You will first import a mesh for

the central catalyst section

(right mouse click)

The hex mesh was created in

ICEM CFD Hex

Set the mesh format to ICEM

CFD and browse to your

working directory

Select CatConvHousing.msh,

set the mesh units to cm, and

click OK to import the mesh

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Importing the Hex Mesh

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You will now import a

tetrahedral mesh created for

the pipe and flange section

Set the mesh format to CFX-

5 GTM file

Select CatConvMesh.gtm,

and click OK to

import the mesh.

Importing the Tet Mesh

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Transforming a Mesh Assembly

The second end section is identical to the

first except that it has been rotated by 180

degrees about the center of the housing

You will copy and rotate the flange section

you imported by 180 degrees about an axis

parallel to the y-axis located at the center

of the catalyst housing

In the Mesh Workspace, select Mesh

Assembly 2 and right-mouse click to

Transform…

This brings up the Mesh Transformation

Editor

Ensure that the CFX-Pre working units are

set to SI System.

(Edit>Options>Common>Units)

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Mesh Transformation Editor

Set the Transformation to Rotation and set

Method to Rotation Axis

In the From boxes enter (0, 0, 0.16)

In the To boxes enter (0, 1, 0.16)

Under Angle, set the Option to Specified and

Angle to 180 degrees

In order to prevent the transformed mesh from

being deleted, enable the Multiple Copies

toggle. Click OK to transform the mesh

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Completed Transformation

Transformed Mesh

Original Mesh

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Defining a Domain

Next we will define the

fluid domain

Click Create, Flow

Objects and select

Domain.

Call the Domain

“CatConv”

Click Ok to Edit the

Domain

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Defining a Domain

On the General Options Panel on the Domain form:

Click in the Location box and hold the <CTRL> key

down and select all three mesh assemblies

(Assembly, Assembly 2, Assembly 3)

Set the Fluids List to Air Ideal Gas

Set the Reference Pressure to 1 atm

On the Fluid Models tab:

Set the Heat Transfer Model Option to Isothermal

and set the Fluid Temperature to 600 K.

Leave all other values at their default and click OK

to apply the form

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Defining a Subdomain

The catalyst-coated honeycomb structure will

be modeled using a subdomain with a

directional source of resistance.

For quadratic resistances, the pressure drop is

modeled as:

To create a subdomain, click on the Subdomain

icon from the main toolbar

Set the Name to Catalyst and click OK.

On the Basic Settings Panel, set the Location to

Assembly and then click the Sources tab

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Setting a Quadratic Resistance

On the Sources panel:

Turn on Sources, Momentum Source/Porous Loss, and Directional Loss Model

Under Streamwise Direction, set the Option to Cartesian Components and set:

X Component to 0

Y Component to 0

Z Component to 1

Under Streamwise Loss, set the Option to Linear and Quadratic Coefs

Turn on Quadratic Coefficient and enter a value of 650 kg/m^4

Click OK to create the subdomain

To create a subdomain, click on the Subdomain icon from the main toolbar

Set the Name to Catalyst and click OK.

On the Basic Settings Panel, set the Location to Assembly and then click the Sources

tab

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Inlet Boundary

Next, we will create inlet and outlet

boundary conditions to the fluid domain

Create a boundary condition called “inlet”

Set the Boundary type to Inlet and the

location to PipeEnd 2.

On the Boundary Details panel, set the

Option to Normal Speed and set a value of

25 m/s. Apply the form.

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Outlet Boundary

Create a boundary condition called “outlet”

Set the Boundary type to Outlet and the

location to PipeEnd.

On the Boundary Details panel, set the

Option to Static Pressure (not Average Static

Pressure) and Relative Pressure to 0 Pa.

Apply the form.

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Boundary Conditions

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Domain Interfaces

Domain interfaces are also used to join dissimilar

meshes together. You will need to create GGI

interfaces between the inlet pipe section mesh and

the catalyst housing and between the catalyst

housing and the outlet pipe section

Click on the Domain Interfaces icon

and set the name to InletSide

On the Basic Settings panel, set the Interface Type to

Fluid Fluid.

Set the Side 1 Filter to All Domains and select

FlangeEnd 2 in Region List 2

Set the Side 2 Filter to All Domains and select INLET in

Region List 1 Click Ok to apply the form.

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Domain Interfaces

Similarly create a second domain interface

named OutletSide


FlangeEnd in Region List 1.


OUTLET in Region List 2. Click Ok to apply

the form.

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Domain Interfaces

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Initialisation

Click on the Global Initialisation icon

You will set a guess for the initial velocity based on

uniform flow through the catalyst housing. If the

inlet velocity is scaled by the ratio of areas between

the inlet pipe and housing cross-section, a value of

approximately 2 m/s results

Under Cartesian Velocity Components, set the

Option to Automatic with Value. Set U and V to 0

m/s and W to –2 m/s (flow goes through in the –z

direction)

Toggle on Turbulence Eddy Dissipation and leave

the Option as Automatic. Apply the form.

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Solver Settings

Click on the Solver Control icon

Set a Physical Timescale of 0.04 s and

set the Maximum Number of Iterations

to 100

Click Ok to apply the form

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Select the Write a Solver File icon

Set File Name to converter.def.

Set Operation to Start Solver Manager.

Turn on report Summary of Interface

Connections

Press OK

A report of the GGI interfaces you created will be

displayed. Click OK in the information window.

Exit Pre and Click Yes on Save Changes window to

save the cfx file

Writing a Definition File

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Defining the Run

When the Define Run form

comes up click the Start Run

button to start the run.

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Launching CFX POST

Click on ‘Post Process’ icon

Choose to shut down the Solver

Manager and click OK to launch

CFX – Post with the current

results file

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Viewing the Domain Interfaces

Turn off visibility of the

Wireframe.

Make InletSide Side CatConv

Part 1 visible and double-

click it in the list.

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Under the Render tab, turn on Draw Lines and

color the lines red. Turn off Draw Faces and

click Apply

Repeat these steps for InletSide Side CatConv Part 2 but color the lines green.

Orient the view as shown on the next slide to see the interface between the dissimilar meshes clearly.

Turn off visibility of the interface boundaries and toggle visibility of the Wireframe back on

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Click on the Create Plane icon in the main tool bar

Create a ZX plane through Y = 0 and color the plane

according to Pressure. You can see the pressure falls

steadily through the housing.

Make the plane invisible and create a vector plot on it.

The flow through the housing is uniform as expected

although there is some separation where the inlet pipe

expands into the flange.

Creating a Slice Plane

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Creating a Polyline

Make the vector plot invisible

You will create a polyline to plot the pressure as a

function of the z coordinate.

Click on the polyline icon from the main toolbar

and accept the default name. On the form, set the

Method to Boundary Intersection.

Set the Boundary List to CatConv default, inlet and outlet

(hold the <CTRL> down for multiple select)

Set Intersect With to Plane 1

Click on the Color tab and choose a bright color for

the polyline. Click on the Render tab and increase the

Line Width to 3. Apply the form.

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Creating a Chart

You will create a chart to plot the pressure as a function of the z coordinate on the polyline you just created.

Click on the chart icon from the main toolbar and accept the default name.

Set the X Axis to Z and the Y Axis to Pressure

Click Apply.

You can see that the pressure drops linearly through the main body of the housing due to the resistance of the catalyst.

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Exporting Data

From the Main Menu select File/Export.

Make sure that Export Geometry Information is

toggled on. This will cause X, Y, and Z values to

be sent to the output file. The connectivity

information could be used to create a file that you

could read back in as a polyline.

Select Pressure in the Select Variable(s) list.

Click the Formatting tab and set the Precision to 3.

Click Save to export the results. The file

export.csv will be written to the current working

directory. You can view this file in any text editor.

cfx 5.7 catalytic converter simulation workshop 11 ansys cfx 5.7

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