cfd pro 14.5 ws05 catalytic converter cfx

2013 ANSYS, Inc. December 12, 2013 1 Release 14.5

14. 5 Release

Workshop 05 Catalytic Converter

Introduction to ANSYS

CFD Professional


Catalytic Converter

This workshop demonstrates flow through a housing that contains a catalytic layer.

To reduce solution times, half of the geometry will be modeled as flow is assumed to be symmetrical

A momentum sink will be implemented in a subdomain to produce the resistance to flow presented by the catalytic layer.

Multiple meshes are used in this simulation. They will need to be connected together in CFX-Pre using domain interfaces.

Catalytic Layer


Full Housing Dimensions:

Inlet duct diameter = 0.4 [m]

Central compartment cross-section = 1 [m] by 1 [m]

Catalytic layer thickness = 0.1 [m]

Total length inlet to outlet = 3.4 [m]

Due to vertical symmetry only half of the geometry is considered

Working fluid is Air at a temperature of 580 K

Flow conditions:

Inlet mass flow = 0.38 [ kg/s ]

Inlet temperature = 580 [ K ]

Outlet static pressure = 0 [ Pa ]

Catalyst resistance coefficient will be calculated later

Simulation Overview


1. Launch Workbench and save the project as CatConv.wbpj

2. From the Component Systems toolbox, drag a CFX system into the Project Schematic and double-click on Setup to open CFX-Pre

3. Right-click on Mesh in the Outline tree and select CFX-Mesh. Import the file ConvMain.gtm

4. Repeat the above step to import ConvCat.gtm

The Outline tree will now show two meshes. Later, the meshes will be connected using Domain Interfaces.

Start Simulation


To complete the mesh, we need to copy and rotate the mesh called ConvMain.gtm.

1. Right-click on ConvMain.gtm in the Outline tree and select Transform Mesh

2. Enter the Apply Rotation settings as shown

3. Enable Multiple Copies and then click OK

Rotate mesh


Composite Regions are labels for groups of existing primitive regions. They make selection easier when domains and boundary conditions are created

1. Select Insert > Regions > Composite Region from the main menu

2. Set the Name to Converter

3. Pick Combination as Union

4. Set Dimension to 3D

This just filters the Regions list to only show 3D regions

5. Pick Assembly, Assembly 2 and Assembly 3 in the Region List (use the icon)

These two assemblies make up the fluid domain

6. Click OK to create the Composite Region

Create a Composite Region


The next step is to create a material with properties representative of air at 580K

In the Materials section of the Outline Tree, right-click on Air at 25 C and select Duplicate. Rename the new material, Air at 580K

On the Material Properties tab change:

Density to 0.609 [kg m^-3] and

Dynamic Viscosity to 2.95e-05 [kg m^-1 s^-1] (first expand Transport Properties)

Create material


1. Right-click on Flow Analysis 1 in the Outline Tree and select Insert > Domain and enter the Name as Converter

2. Set Location to Converter and the Domain Type to Fluid Domain

3. Select Air at 580K as the Material and leave the Reference Pressure at the default value of 1 [ atm ]

4. On the Fluid Models tab set Heat Transfer Model to None

5. Leave the Turbulence Option set to the default k-Epsilon Model

6. Click OK to create the domain

Define Fluid Domain


The catalytic layer will be represented as a resistance to flow, i.e. a momentum sink. The sink is equivalent to a pressure gradient. When flow is turbulent, the pressure drop tends to scale with velocity2 and can expressed in the form:

For the catalyst layer Kloss is 400 m-1.

Due to the structure of the layer, there is much more resistance in the direction transverse to flow. ANSYS CFX offers a directional loss model specifically for this type of case.

Define resistance

iloss

i

UKdx

dp

2


1. Right-click on Converter in the Outline Tree and select Insert > Subdomain

2. Set the Name to Catalyst and the Location to B71

3. On the Sources tab check boxes for Sources, Momentum Source/Porous Loss and Loss Model. Set Option to Directional Loss

4. Enter 0 for the X and Y Component, and 1 for the Z Component to define the Streamwise Direction

5. For Streamwise Loss pick Permeability and Loss Coef, check the box for Resistance Loss Coefficient and set the value to 400

6. Leave the options for the Transverse Loss as the defaults

Define resistance


Next create the Inlet boundary condition:

1. Define an Inlet boundary condition named inlet using the Location named PipeEnd

Insert the boundary condition by right-clicking on the Converter domain so that the boundary condition is created in the correct domain

2. On the Boundary Details tab set a Mass Flow Rate of 0.38 [ kg s^-1 ] and use the default turbulence values

Now create an Outlet boundary condition:

1. Define an Outlet boundary condition in the fluid domain named outlet at the Location named PipeEnd 2

2. On the Boundary Details tab set Average Static Pressure to 0 [ Pa ]

Boundary Conditions


Create a Symmetry boundary condition

1. Right-click on Converter to insert a boundary called symmetry

2. Set the location to Entire Symmetry and PorousSym (When an Assembly is copied, a 2 is appended to the names of the new regions that are created. New composite regions are also created that group together the old and new regions, these are called Entire

Boundary Conditions


Domain Interfaces are required to connect the meshes

1. Right-click on Interfaces in the tree and select Insert > Domain Interface

2. Enter the Name as UpstreamInterface

3. Select the Interface Type to Fluid Fluid

4. For Interface Side 1 pick FluidSide from the Region List

5. For Interface Side 2 pick PorousSideUp from the Region List

6. Leave the Interface Models and Mesh Connection Method at their default settings. Click OK to create the interface

7. Create a second Fluid Fluid Domain Interface named DownstreamInterface with FluidSide 2 and PorousSideDown as side 1 and 2, respectively

NOTE: Ideally the meshes would have been conformal so that no interfaces were required

Domain Interfaces


Now set the initial conditions:

1. Right-click on Flow Analysis 1 and select Insert > Global Initialization.

2. Under Cartesian Velocity Components set Option to Automatic with Value

3. Set the U, V, W velocity components to 0, 0, 1 [ m s^-1 ]

4. Leave the option for Static Pressure as Automatic and leave Turbulence as Medium (Intensity = 5%)

5. Enable the Turbulence Eddy Dissipation check-box at the bottom of the panel

6. Click OK

Initialization


Close CFX-Pre

Save the Workbench project

In Workbench double-click Solution to launch the CFX-Solver Manager

Obtaining a solution


1. Create a new Monitor Plot (Workspace > New Monitor) to monitor the Imbalances for each equation during the solution

2. Change the scale for the Imbalance plot so that it uses a log scale by right-clicking on the monitor, selecting Monitor Properties, then enabling the Use Logarithmic Scale toggle on the Range Settings tab

3. Check the imbalances at the end of the run in the OUT file

Monitoring the Solution


1. Close the CFX-Solver Manager

2. Save the project

3. Double-click Results to launch CFD-Post

4. Make a vector plot of Velocity on the symmetry plane by picking the Location called symmetry

5. Make a Contour Plot of Pressure at the same location

CFD-Post


The plot of pressure contours and velocity vectors show the effect of the resistance on the flow.

Streamlines show how the resistances leads to a more uniform distribution of flow

CFD-Post


1. Switch to the Expressions tab

2. Right-click on Expressions and select New

3. Enter the Name as deltaP and then enter the Definition as: areaAve(Pressure)@FluidSide - areaAve(Pressure)@FluidSide 2. If using the drop-down menus, choose Locations > Composite

4. Click Apply to evaluate the expression

Calculate pressure drop


Next you will create a plot of Pressure along a line. First you must create the line:

1. Create a new Line object using the Location menu on the main toolbar

2. Define the line using the Two Points Method between the points (0, 0.5, 1.2) and (0, 0.5, -2.2)

3. Set the Line Type as Sample and set the Number of Samples to 100

4. Click Apply

Chart


5. Create a Chart object using the chart icon on the main tool bar

6. On the General tab of the chart details enter the Title as Pressure Through Centre Line. Make sure Display Title is checked and leave the Type as XY

7. On the Data Series tab set the Name to pressure and the Location to Line 1

8. On the X Axis tab set the Variable as Z and on the Y Axis tab set the Variable as Pressure then click Apply

Chart

The upstream side of the catalyst layer is at Z = -0.45m and the downstream side at Z = -0.55m. The pressure drop across the resistance region can been seen

cfd pro 14.5 ws05 catalytic converter cfx

Documents

release workshop

outline tree

composite regions

fluid domain

regions composite region

flow conditions

domain interfaces

inlet mass flow