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CFX 5.7 Heating Coil Simulation Workshop 12 ANSYS CFX 5.7

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Text of CFX 5.7 Heating Coil Simulation Workshop 12 ANSYS CFX 5.7

PowerPoint Presentation*
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.
CFX 5.7
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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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CFX 5.7
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Copy the following files to your working directory
HeatCoil.wbdb & HeatCoil.agdb
Click on the CAD2Mesh icon to start the ANSYS Workbench environment
CFX 5.7
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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.
CFX 5.7
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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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Suppress or unsuppress geometry parts/bodies for easier viewing
Mouse Usage:
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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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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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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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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
CFX 5.7
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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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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
CFX 5.7
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© 2004 ANSYS, Inc.
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
CFX 5.7
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© 2004 ANSYS, Inc.
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.
CFX 5.7
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© 2004 ANSYS, Inc.
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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© 2004 ANSYS, Inc.
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
CFX 5.7
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Click on None to select the defining surfaces
Box Select the entire geometry
Click Apply to accept the selection
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© 2004 ANSYS, Inc.
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
CFX 5.7
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© 2004 ANSYS, Inc.
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
CFX 5.7
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© 2004 ANSYS, Inc.
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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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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© 2004 ANSYS, Inc.
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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Return to the Project Page by clicking the Project Tab
Save the project and exit Workbench
CFX 5.7
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CFX 5.7
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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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Next we will define the working fluid around the coil
Click Create, Flow Objects and select Domain.
Call the Domain “fluid”
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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 initial
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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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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”
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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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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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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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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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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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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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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© 2004 ANSYS, Inc.
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
CFX 5.7
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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
CFX 5.7
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© 2004 ANSYS, Inc.
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
CFX 5.7
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© 2004 ANSYS, Inc.
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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© 2004 ANSYS, Inc.
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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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
CFX 5.7
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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
CFX 5.7
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© 2004 ANSYS, Inc.
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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© 2004 ANSYS, Inc.
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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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 run should stop after about 30 iterations
Diagnostics will be generated by the solver in the text window at right.
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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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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:
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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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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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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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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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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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© 2004 ANSYS, Inc.
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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© 2004 ANSYS, Inc.
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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© 2004 ANSYS, Inc.
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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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…