CFX 5.7
Heating Coil Simulation
Workshop 12
ANSYS CFX 5.7
Workshop
CFX - 5.7
October 1, 2004Inventory #002157
WS12-2CFX 5.7© 2004 ANSYS, Inc.
Introduction
The objective is to set up, solve and post-process a simplified CFD problem which
illustrates fluid flow and conjugate heat transfer.
The mesh resolution used in this workshop will not necessarily obtain accurate results,
but will enable the participants to work through test cases in the limited time available.
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WS12-3CFX 5.7© 2004 ANSYS, Inc.
Workshop Outline
Analysis of a heating coil surrounded by moving fluid
Open an existing workbench project containing the Design Modeler geometry
Open CFX Mesh: Set mesh parameters and create mesh
Preprocess: set fluid domain physics, boundary conditions, initial conditions, solver
parameters
Solution: monitor residuals, review out files
Post-process
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Heating Coil Workshop
Double click on to start the CFX5.7 launcher ...
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Getting Started
Ensure that the Working Directory
is set
Copy the following files to your
working directory
HeatCoil.wbdb & HeatCoil.agdb
Click on the CAD2Mesh icon to
start the ANSYS Workbench
environment
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Starting CFX Mesh
Select Open Project and
open the HeatCoil.wbdb
database.
On the project page, select
on the Design Modeler
database HeatCoil.agdb
With the Design Modeler
database selected, click
on Generate CFX Mesh.
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Mesher Environment
Mesher window appears
as tab on the Project Page
Layout is similar to Design
Modeler with parts tree on
left
Meshing Progress from
top to bottom of Tree
Feedback from mesher
appears at bottom left
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Mesher Environment
Perform tree
functions by right-
clicking on objects
Suppress or
unsuppress geometry
parts/bodies for
easier viewing
Mouse Usage:
to rotate (default)
+ shift to zoom
+ ctrl to translate
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Mesher Environment
Left clicking on selected
objects in the tree allows you
to change attributes of that
object
To change the geometry view
from solid (opaque) to
transparent mode, left click on
Geometry
Set % Transparency to 67
using the slider bar or by
typing in a number.
Experiment with different
transparencies and shine
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2D Region Creation 1
Define 2D regions for
placement of CFD
boundary conditions
Right-click on
Regions to Insert a
new Composite 2D
Region
Composite regions
can consist of one or
more surfaces
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2D Region Creation 2
Create the 2D Region
“cinlet” to define the
nearest end of the
cylinder
To select a location
on the geometry,
click None under
Composite 2D Region
at bottom left
Pick the nearest end
of the cylinder
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Save Often
Save your work often !
Save after each
significant change to
the mesh definition
Click Save As … and
save in your working
directory
For subsequent
saves, simply click
Save
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2D Region Creation 3
Surfaces selected for
2D regions will
appear as green in
the viewer window
Unfinished region
definitions appear
with a red-circled
exclamation mark
Click Apply to finish
defining the new 2D
region. Marks should
disappear
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2D Region Creation 4
Create 3 more 2D
regions:
coutlet for the far end
of the cylinder
hinlet for the end of
the coil nearest to the
inlet
houtlet for far end of
the coil
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2D Region Creation 7
We will now create a region coil
that defines the surfaces of the
coil which will be in contact with
the fluid.
Set the display to transparent so
that the interior structures of the
geometry become visible
Left click the Geometry object in
the tree
Use the slider bar to adjust the
transparency
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2D Region Creation 9
Orient the geometry so
that you are viewing the
side of the cylinder
Insert a new 2D Region “coil”
Click on None to set the Location
Box select the coil to
include all the coil
surfaces. Note that the
ends of the coil have
already been assigned to
hinlet and houtlet
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2D Region Creation 6
All the selected coil surfaces
should turn green.
Holding down the control key
select the two end surfaces of
the coil (previously defined as
hinlet and houtlet) to deselect
them
Click on apply to assign the
selected surfaces
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Mesh Controls 1
Some parameters are required to
control the density of the
tetrahedral mesh produced by
CFX-Mesh
Under Mesh in the Object Tree,
click on Default body spacing
and set to 0.12 mm.
Click on Default Face Spacing.
Set Angular resolution to 30
Degrees, Minimum and Maximum
Edge Lengths to 0.006 and 0.12
mm respectively
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Mesh Controls 2
Click on Inflation. Set
the number of Inflated
Layers to 3. Set the
Expansion Factor to
1.7.
Inflation controls the
mesh near the walls of
the geometry (more
later …)
Click on Options. Set
Overwrite Existing GTM
file to Yes.
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Mesh Controls 3
Click on Preview. This section of
the tree controls mesh
visualization. Set Mesh Render
Mode to Wireframe
Set the mesh Face Colour Mode to
Uniform and choose a color by
clicking on the colored bar
Next, we will select the surfaces
on which to display the finished
mesh.
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Mesh Preview 1
Mesh Preview allows the definition
of surfaces on which to view the
mesh before exporting to CFD
Right click on Preview and Insert a
Preview Group. Label the group
“coilsurface”.
Click on None under Preview
Group to select surfaces and box
select the entire Coil
Click Apply to accept the selection
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Mesh Preview 2
Create a second Preview
Group called “all”
Click on None to select the
defining surfaces
Box Select the entire
geometry
Click Apply to accept the
selection
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Mesh Generation 1
CFX Mesh generates surface
meshes first, then makes the
volume mesh
To generate a surface mesh for the
coil, left-click on the coilsurface
Preview region and select Generate
This Surface Mesh
A progress bar appears at the
bottom of the window.
When the coil surface mesh is
complete, it appears in the viewer
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Mesh Generation 2
To generate a surface mesh
for the coil, left-click on the all
Preview region and select
Generate This Surface Mesh
A progress bar appears at the
bottom of the window.
When the surface mesh is
complete, it appears in the
viewer
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Mesh Generation 3
Next we will define the characteristics of the
mesh near the walls of the geometry
Insert Inflated Boundary “cylinder” and set
the maximum thickness to 0.12 mm
Click on None next to Location box and
select, the inner and outer cylinders. (Note:
Use the control key for multiple selections)
Click on Apply to accept
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Mesh Generation 4
Now we will view the changes produced by
defining inflation.
Click on Preview and Set Mesh Render
Mode to Solid Face
Right-click on Preview region all and
generate the surface mesh
Mesh appears as solid and shaded. The
meshed surfaces shown represent the
interface between the inflation layer and
the tetrahedral mesh
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Mesh Generation 5
Generate the volume mesh (this step
writes out a mesh *.gtm file)
Use the icon at the top right corner of
the meshing window,
Or right click on the Mesh object in
the tree
Volume meshing uses the constraints
created during surface meshing
A progress bar will appear at the
bottom left of the mesher window
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Saving the Mesh file
Save the CFX Mesh
database.
Return to the Project
Page by clicking the
Project Tab
Save the project and exit
Workbench
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Starting CFX-5 Pre
Click on CFX-Pre 5.7
The CFX-Pre Splash Screen should appear
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Starting CFX-5 Pre
Click on Open Simulation
Set the file type to be GTM Database
Select the GTM file written out by CFX Mesh (HeatCoil.gtm)
Click on Open to start CFX Pre.
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Preprocessing 1
Click on the Physics Tab to start defining the problem parameters
Click Create, Flow Objects and select Simulation Type.
Set the Simulation Type to Steady State.
Click Ok
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Preprocessing 2
Next we will define the working fluid around the coil
Click Create, Flow Objects and select Domain.
Call the Domain “fluid”
Click Ok to Edit the Domain
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Preprocessing 3
The Edit Domains Form has three sections
Under General Options set the location to B2.P3, the fluid to Water and the reference Pressure to 1 atm
Under Fluid Models, set the Heat Transfer Model to Thermal energy and the Turbulence Model to k-Epsilon
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Preprocessing 4
Under Initialization, set the fluid Relative Pressure to 0 Pa. This is the pressure relative to the reference pressure set for the domain
Click on the checkbox next to Turbulence Eddy Dissipation to set it
Leave the initialization as automatic
Click OK to save all the Domain settings and close the form
Click on initialconditions checkboxto activate initialization
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Preprocessing 5
Note that the Tree at the left now has a new object called fluid
This is the domain created in the last few steps
Create a second domain and call it coil
Click OK to edit the coil domain
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Preprocessing 6
Set the Location to B1.P3. This should highlight the coil mesh in the viewer window
Set the Domain Type to Solid and select Copper from the Solids List
Under the Solid Models tab, note the the Heat Transfer Option is already set to Thermal Energy
Leave the Radiation Model as None
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Preprocessing 7
Click on Initial Conditions to Activate initialization
Set the Temperature Option to Automatic (this is default if the Initialization is not activated)
Click OK to save the domain settings and exit the form
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Preprocessing 8
Next we will specify a heat source in the coil location
Create a Subdomain
Label it “heatsource”
Make sure the Domain is set to coil
Click OK to accept the selection
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Preprocessing 9
Set the location to B1.P3 (Note: the heat source will be specified for the entire volume of the coil)
Under The Sources Tab, set the Energy Sources Option to Total Source
Specify a total heat source of 50 kg m^2 s^-3 (50 W)
Click OK to save the subdomain setting and exit the form
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Preprocessing 10
Next, we will create inlet and outlet boundary conditions to the fluid domain
Create a boundary condition called “inlet”
Make sure that the domain is set to fluid
Click OK to accept and specify the inlet conditions
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Preprocessing 11
Edit the inlet boundary conditions
Under Basic Settings, set the Boundary Type to Inlet and the Location to cinlet
Under Boundary Details, set the Normal Speed to 0.1 m/s and the Temperature to 300 K
Click OK to save the boundary settings and exit the form
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Preprocessing 12
Note that creating objects automatically adds them to the tree at left
To make changes to any object, simply double click to bring up the appropriate form
The inlet boundary is shown as flow arrows in the viewer
Create a second boundary condition called “outlet” for the domain fluid and click OK to edit it
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Preprocessing 13
Edit the outlet boundary conditions
Under Basic Settings, set the Boundary Type to Outlet and the Location to coutlet
Under Boundary Details, set the Mass and Momentum Option to Average Static Pressure
Set the Relative Pressure to 0 Pa
Click OK to save the boundary settings and exit the form
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Preprocessing 14
We are now ready to set the CFD Solver Specifications
Create a Solver Control Flow Object
This will bring up a form on which the discretization scheme and fluid/solid time scales can be set
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Preprocessing 15
For most problems, only the Basic Settings Tab is used
The default discretization is High Resolution and is also most accurate and robust.
The fluid will have a much shorter timescale than the solid
Use a physical timescale of 0.01 s for the fluid and 5 s for the solid
Set the Conservation target for equation balances to 0.01
Click OK to save and exit the form
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Preprocessing 16 (optional)
Click on File -- Export ccl to save the problem setup
Turn off ‘Save All Objects’ and select the Flow & Library objects.
Save the setup as coil.ccl
Saving setup files will allow the boundary conditions to be read in quickly if the grid is changed
The .ccl file is a text file that can be edited using any text editor
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Preprocessing 17
Click on File -- Write Solver (.def) file to write a file to the solver
Save the setup as HeatCoil.def
Set the Operation to Start Solver Manager and turn ON the Report Summary Interface Connections option.
Click OK to save and exit the form
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Preprocessing 18
Minimize the Solver Manager window.
Notice that a domain interface has been automatically created by PRE, to connect the fluid and solid domains.
Click OK on the information window.
Save the CFX Pre database and exit.
Restore the Solver Manager window.
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Starting the Solver
On the Define Run form click on Start Run to start the solver
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The Solver Manager Workspace
All the functions available from the icons at the top of the Solver Manager window are also available from the Workspace menu
Use the Workspace menu or the icon tool tips to see what various icons do
Note that once a workspace has been changed, this custom setting can be saved and recalled when needed
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Viewing the residual plots
Click on the Heat Transfer tab to see the solution residuals for the solid (coil) and fluid energy equations
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RMS Residual Diagnostics
Click on the Turbulence Quantities tab to see the solution residuals for the fluid turbulence
The text window at the right shows the solution progress and the numerical values of the solution residuals
As the solution progresses, the Rate of convergence should fall below 1.0
Values from 0.4 - 0.8 are indicative of a well chosen timestep
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Changing the Layout
The Solver Manager can be reconfigured to view all diagnostics simultaneously.
Click on the Toggle Layout Type icon at the top of the Solver Manager Window
Click on the Arrange Workspace icon afterward to organize the extra windows that appear, or use the Workspace Menu
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Multiple Residual Plots
Seeing all the solution residual plots simultaneously makes it easier to diagnose the trends in a run
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Changing the plot windows
The RMS (root mean square) residuals are the default plot for the Solver Manager
To see the maximum residuals, click on the View Max Residuals icon at the top of the Solver Manager window
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Interpreting Residual Plots
All the plots should change to show the maximum residuals
Maximum residuals will generally be a one or more orders of magnitude higher than RMS residuals
Note that the convergence rates on the right are now between 0.5 and 0.9
Flat residual plots indicate that the timestep should be increased
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Changing individual plot formats
Right clicking on the residual plots allows the plot format to be changed
Right click on the Momentum and Mass Max residuals plot and select Monitor Properties
The Monitor Properties form for Momentum and Mass Balances should appear
Change the Window Label to Momentum and Mass Balances
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Changing individual plot formats
The Range Settings tab allows the axes ranges of the residual plots to be changed
Click the Plot Lines tab and remove the checks from the checkboxes beside Max P-Mass, MAX U-Mom, MAX V-Mom and MAX W-Mom
Click Apply to update the plot title and remove the Max residual plotlines
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Plotting Mass Imbalances
The Plot Lines window allows a number of diagnostic variables to be plotted. These are shown in a tree structure
Collapse the RESIDUAL tree (by clicking the minus sign) to view the entire list
Since the equation imbalances are not shown in the text window, we will plot these
Expand the IMBALANCE tree so that the required plots can be selected
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Plotting Mass Imbalances
The IMBALANCE tree shows all equations for which an imbalance can be computed
Note that the solid energy balance is shown separately
Check off P-Mass, U-Mom, V-Mom and W-Mom under fluid
Click on Ok to update the plot settings and exit the form
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Plotting Energy Imbalances
The Momentum and Mass window now shows all the changes
Note that the balances show a different trend from the residuals.
Create a new Monitor to plot energy imbalances. (Workspace >New Monitor)
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The completed run
The run should stop after about 30 iterations
Diagnostics will be generated by the solver in the text window at right.
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Final momentum balances
Maximize the view of the text window
The Boundary Flow and Total Source Term Summary shows the convergence level of the equations
Click on the Post Processing button to launch CFX-Post with the current results file.
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Post Processing
CFX Post starts with a wireframe view of the geometry
The boundary condition and interfaces created in CFX-Pre appear in the tree to the left
Test Mouse Usage:
to rotate
to translate
to zoom
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Creating a Locator Plane 1
Start the Post Processing session by creating a YZ locator plane.
This plane will be used to locate plots of solution variables on a cross section of the geometry
Leave the name as Plane1
Click OK to set the plane attributes
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Creating a Locator Plane 2
Note that Plane 1 has been added to the tree on the left under User Locations and Plots
The plane attributes can be set in the form that appears under the tree.
Leave all the default settings as they are and click Apply
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Creating a Contour Plot 1
Hide Plane 1 by clicking the checkbox to the left
Create a contour plot using the Create Menu or the icons across the top of the viewer
Leave the name as Contour 1 and click OK
This contour plot will be associated with Plane 1 to view temperature and velocity
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Creating a Contour Plot 2
Set the attributes of the Contour plot by changing the properties in the form below the tree
Set the location to Plane 1
Change the Variable to Temperature
Change the Range to Local
Click Apply to save
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Customizing the Legend 1
The contour plot of temperature should appear
Next, we will change the format of the legend to increase the view area
Expand the View Control object in the tree at left
The Default Legend object should be listed
Double click to edit the legend
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Customizing the Legend 2
The Default Legend form should appear under the tree
Change the Title Mode to Variable and Location
Click the Appearance tab to change the legend text
Set the Precision to 0 and change Scientific to Fixed
Click Apply to update the legend in the viewer window
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Coil Temperature
Note that the coil temperature changes from inlet to outlet
The coil creates turbulence, which improves heat transfer from the downstream portion of the coil
Downstream sections are therefore slightly cooler
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Fluid Temperature 1
Change the range of the contour plot to see what is happening to the fluid temperature
Double click on Contour1 under User Locations and Plots
Change the Range from Local to User Specified
Set the Min and Max to 300 K and 400 K respectively
Click Apply to update
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Fluid Temperature 2
The fluid gets progressively hotter as it moves along the coil
The largest temperature increases in the fluid corresponds to areas where the cooling water has stagnated
The smallest temperature increases in the fluid correspond to areas where the flow velocity is higher
Create a contour plot of fluid velocity on Plane 1
Create a tangential vector plot of fluid velocity on Plane 1.
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Streamline Plots 1
Streamline plots give the best visualization of flow around the coil
Under User Locations and Plots, hide the Vector and Contour plots by clicking on the checkboxes
Use the Create Menu or icons to create a Streamline plot
Leave the name as Streamline 1 and click OK
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Streamline Plots 2
In the Streamline 1 form, set Start From to inlet
Set Reduction to 2 (streamline for every second node on inlet)
Under the Color tab, set Mode to Variable
Set Variable to Temperature and Range to User Specified
Set Min and Max to 300 and 400 K as before
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Streamline Plots 3
Click on the Symbol tab, to set the appearance of streamlines
Change the Stream Type to Tube
Set the Tube Width to 2.5
Leave the # sides as 8
Click Apply to update the plot in the viewer window
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Streamline Plots 4
The streamline plot shows the flow path of a fluid “parcel”
Streamlines can be coloured by pressure, velocity, turbulence variables
Experiment with different types of streamline colouring