workshop 5: basic workflows - mr-cfddl.mr-cfd.com/tutorials/ansys-fluent/fluent_meshing...in the...

© 2011 ANSYS, Inc. December 21, 2012 1 Release 14.0

14.5 Release

Introduction to ANSYS Fluent Meshing

Workshop 5: Basic Workflows


Workshop Description

This workshop will introduce the different workflows available when meshing

an assembly when different meshing goals are sought.

Learning Aims

This workshop will cover how to:

• Extract the fluid volume only from a set of open solid assemblies

• How to generate a mesh for conjugate heat transfer where there is only one type of solid material

• How to generate a mesh for conjugate heat transfer where there are multiple solid materials

Introduction


• Open the Fluent Launcher by clicking the Windows Start menu, then selecting Fluent. 14.5 in the Fluid Dynamics sub-menu of the ANSYS 14.5 program group.

• Enable Meshing Mode under Options. • Set Working Directory to the area where files are • Click OK to start Fluent in meshing mode.

Starting Fluent in Meshing Mode


File Import CAD... Ensure that Import Single file is enabled. Select the file “WS5_T-junction-demo.agdb” Enable Import Curvature Data from CAD. Retain the value of 1 for Scale Factor and the selection of body in the One zone per drop-down list, respectively. Click the Advanced... button to open the CAD Advanced Options dialog box. • Enable Save PMDB in the File group box. • Select mm in the Length Unit drop-down list. • Select Conformal Tessellation in the Tessellation group box.

– Specify values of 1 and 10 for Min Size and Max Size, respectively. – Enable Edge Proximity and select 2 Cells Per Gap

• Retain the selection of Import Named Selections in the Named Selection group box. • Click Apply and close the CAD Advanced Options dialog box. • Click Import in the Import CAD Geometry dialog box. • Close the Import CAD Geometry dialog box.

Import the CAD Geometry


The General Workflow is:

-Import CAD

-Close Holes/Gaps

-Set Sizing Functions

-Extract Edges

-Wrap

-Sew

-Improve

-Volume Mesh

-Clean

-Export to Solver

General Workflow

Model Preparation

Surface Mesh Generation

Volume Mesh Generation

Exact process depends on desired outcome


Once the CAD import is complete, click on

Manage

Select all the objects in the Objects list and click Draw

Geometry Overview


We can make the following observations about our model:

• It has conformal mesh

• There are four independent solids

• There is no object representing the fluid volume

• There are no caps

• There is a gap between two objects Solid-1 and Solid-2

Geometry Observations


• Zoom in the gap area. We would like to measure the gap distance

• Click in the Graphics Window and use the hot key Ctrl+N to activate the node selection filter

• Using RMB select two mesh nodes which roughly oppose each other.

• The nodes will be marked with a red circle around them. The node IDs show up in the Fluent window (numbers may not match)

• With the two nodes use the hot keys Ctrl+D to calculate the distance between these two nodes. We will use 5mm as the representative gap distance

Model Preparation-Gap Removal


• Click on Objects Manage

• Select the objects in the Objects list and observe the type in the Object Type pull down menu. These are geom type objects, which is the default type object after geometry import

• The Gap Removal tool that we are about to use does not work with geom type objects as these are assumed to be disconnected, so we need to change the object type to wrap to allow this.

• Select all the objects, select object type wrap and then click Change Type.

• Click Yes to the pop-up window/question



• Click on Remove Gaps

• The Remove Gaps panel opens

• Switch to zone filter using ctrl+Z hot key. Ensure no entities are selected in the window by clearing selections using F2 hot key.

• Select the Face Zones solid-1 and solid-2 as shown using RMB in the graphics window

• Hit the hot key ctrl+B to select objects in the list based on selected faces in the graphics

• Click List to see relative priorities

• Note we could decide which boundary is moved by choosing “Low to High” or “High to Low” based on this priority information. Here we will just take the default.

• Enter 5 in the field for Gap Distance

• Click Remove



Before Gap Removal

After Gap Removal



• We will need to create three cap surfaces

• Two of them will represent Velocity Inlets and one them will represent a Pressure Outlet

• Click on Caps under Create as shown

• Choose all objects and click Draw

Model Preparation-Create Caps

1

2 3


• Type inlet under the Object Name field

• Select velocity-inlet under Type

• Select Edge under the Entity Type (this will also set the selection filter to edge type)

• Select Create Edges to automatically extract edges for the capping object at creation

• Select Auto Redisplay (updates graphics automatically after cap creation)

• Zoom close into the area numbered 1 in the previous slide.

• RMB select one of the edges at the inlet. The selected edge is marked with bold red color (the circle in the image is for better identification of the edge-any edge along the edge of the inlet would serve the purpose

• Click Create



• Fluent creates and re-meshes a cap at the inlet.

• Follow the same procedure for the caps needed in areas 2 and 3.

• For area 2 specify inlet2 for Object Name and velocity-inlet for Type

• For area 3 specify outlet for Object Name and pressure-outlet for Type


1

2

3


• We need to create sizing functions in preparation for meshing. Click on Create Size Functions in the task page

• In the Size Functions panel, under Global Controls modify the entries as shown in the figure and click Apply

• Click Create Defaults to create a default set of sizing functions

• The default size functions appear in the list. We will now modify some of them to better address the features of our particular model

• Select all the Boundary Zones in the list and click Draw. Then click Draw Sizes to show min/maxsizes in the graphics.

Generate Size Functions


• Select the default-edge-curvature enter 10 under Normal Angle and click Change.

• We are doing this to ensure that the high curvature bolt-holes are resolved correctly as the default of 18 is conservative to give coarse default mesh



• Perform the same step as before, this time selecting the default-face-curvature and specifying the same Normal Angle 10.

• Click Change

• Click Close



• Click on Objects and then Manage and select only the solid-1 object. Click Draw. Use ctrl-a hot key to centre the graphics

• Click on Create Material Point in the task page

• Click on the graphics window and then type Ctrl+N hot key to active the node selection filter

Material Point Creation


• With RMB click select two nodes in such a way that the middle point of the line connecting them falls clearly in the open volume and it is not very close to the solid. Rotate the model as needed


First Point Second Point


• Type flow-volume in the Name field

• Click Compute. This calculates the coordinates of the mid-point of the line connecting the two selected nodes. Note that the numbers you see may differ from those shown

• Click on Draw. The material point is now rendered in the graphics window as shown here


If the position is satisfactory, then click Create and the material point will be created. Click List to see a list of active material points.


• Alternatively, click on the graphics window and then type Ctrl+Z to active the Zone selection filter

• RMB click on the object and then click Compute

• De-select and then re-select Draw to re-render the new Material Point

• Name the new point as flow-volume-alt

• You see that the material point is at the centroid of the Face Zone selected

• Click Create and then List to list the available material points

Material Point Creation-Alternate Approach


• CAUTION: the alternate approach may result in a material point that is not in the flow volume if the part is not convex.

• Having multiple material points for the same volume does not pose any issues but should we elect to eliminate one, please type the following text command on your Fluent window

– /meshing/material-point/delete-material-point

– Type “flow-volume-alt” when prompted for a fluid zone name

Material Point Creation-Alternate Approach


• Now we have completed the model preparation by creating caps and closing the gap between two objects and we should save our current setup.

• Select File Write and save the mesh file

– T-junction-setup.msh.gz

• We shall now explore the different workflows that are available to get to a fully connected surface mesh for volume meshing

Model Preparation Complete


Problem Statement

As a CFD user, I was given a set of CAD file(s) of an assembly consisting of solids and I am tasked with simulating the flow in the flow region loosely defined by these solids.

Solution

After preparing the geometry, I need to extract the Fluid volume. To achieve that I would have to:

-Create a Material Point that resides in the space where Fluid with flow (Done in Model Preparation stage) -Extract the Fluid volume using the Fluid Surface approach with either cut-wrap or shrink-wrap -Grow prisms in the Fluid Region and a Volume mesh using Auto Mesh

Extracting the Flow volume


• Read the mesh T-junction-setup.msh.gz

• Click on Wrap

• Select all the objects in the list

• Under Target select Fluid Surface

• Under Method select cut-wrap

• Under New Object Name type extracted-fluid

• Pull down the menu under Material Point and select the material point “flow-volume”

• Click Wrap

Extracting the Flow Volume using Cut-Wrap


• The wrapping process will take a few minutes, depending on the speed of your computer.

• Once complete, click on Manage and then select the object extracted-fluid

• Before you click Draw disable Draw Edge Zones from the Object Options in the main Fluent window to improve the clarity of the display

• Now click Draw



• The extracted flow volume is displayed.

• Close examination of the mesh reveals however that it is not appropriate for volume meshing just yet and it needs to be improved.



• Click on Improve under Surface Mesh

• Select the extracted-fluid object from the Objects List

• Without changing anything else click Apply

• This process creates a Mesh object extracted-fluid-14:9

• From the improve panel, select extracted-fluid-14:9 and click Draw




Before Improve After Improve


• We will now examine the quality of the wrapped mesh. Before we do that, we need to activate the appropriate face group that would allow us to select the appropriate zones for quality report.

• Click Groups as shown

• On the Face Groups list select the _mesh_group_extracted-fluid-14:9

• Click Activate

• Click Close



• Use the Menus and navigate to Display Plot Face Distribution

• You see that only the Boundary zones in the group that we activated are listed.

• Select them and click Plot


Good surface quality observed

Save the mesh file as cut-wrapped.msh.gz


• We can now repeat some the steps to extract the Flow Volume using Shrink-Wrap. Not all of the steps will be explicitly mentioned as they are the same as with the Cut-Wrap

• Open the Object Manage panel.

• We will delete the newly created Cut-Wrap objects (not necessary but useful for clarity)

• Select the two objects as shown

• Click Include Faces and Edges to delete both the object definition and the entities it references

• Click Delete

Extracting the Flow Volume using Shrink-Wrap


• Click on Wrap

• In the Wrap panel select inputs as shown.

• Note that now we are selecting shrink-wrap under Method

• Click Wrap



• The Shrink-Wrap operation will take a few minutes depending on the speed of your computer.

• Once done, Draw the object extracted-fluid




Cut-Wrap Shrink-Wrap


• Click on Improve under Surface Mesh

• Select the extracted-fluid object from the Objects List

• Without changing anything else click Apply

• This process creates a Mesh object extracted-fluid-14:9

• From the improve panel, select extracted-fluid-14:9 and click Draw



Mesh after Improve



Problem Statement

As a CFD user, I was given a set of CAD file(s) of an assembly consisting of solids and I am tasked with simulating the flow in the flow region as well as the heat transfer into and from the solids. All solids are made of a single material and in order to simplify my model setup, they need to be a single zone.

Solution

We would need to

-Create a material point to represent the Flow (done in Model Preparation stage)

-Wrap all solid materials together to create a single solid material

-Sew the single solid material with the caps to create a unified model

-Mesh using Auto Mesh

Meshing for Conjugate Heat Transfer with a single solid material



• Click on Objects and then Wrap

• Select all the solid objects in the Objects list

• For Target select Unified Solid Surface

• For Method select cut-wrap – Note: either cut-wrap or shrink-wrap can be used.

We will use cut-wrap for the remainder of this workshop

• Under New Object Name type single-solid

• Click Wrap

Conjugate Heat Transfer with a single solid material


• Select the newly created Object single-solid and click Draw

• Use the clipping planes to cut the model with a yz plane

• You will see that there is no dividing wall between what used to be different solids before


Unified Solid

Multiple Solids


• Click on Sew under Surface Mesh

• In the Object list select the single-solid as well as the inlet, inlet2, outlet as shown

• Type sew-model under New Object Name

• Click Sew



• The process will take a few minutes depending on the speed of your computer. When done a new object named sew-model will appear on the Objects list. Click Draw

• Note: The single solid is made up of separate faces but it is a single object without dividing walls between the previously existing individual solids.



There are no dividing walls between the previous objects



• Use the Menus to navigate to Display, Plot, Face Distribution

• Select the _mesh_group_sew_model boundary zone group. All boundary zones associated with the sew model

• Click Plot



• The mesh quality is very good but it would be instructive to see how this could be improved

• Click on the Improve button

• Select the sew-model

• Specify 0.6 under Quality Limit

• Click Improve

• The maximum skewness is now 0.6 down from 0.74



• To create the volume mesh click on Auto Mesh

• Select the sew-model under Object

• Select the fluid-volume material point under Material Points

• Make sure that the Keep Solid Cell Zones is checked

• Click Mesh



• Use the Menus to navigate to Mesh Manage

• As you can see, there are two distinct Cell Zones created, the fluid-volume and single-solid


Save the mesh as single-solid.msh.gz


Problem Statement

I am given a set of CAD files containing a assembly of different solid bodies, each made of a different material and I am tasked with simulating the flow in the flow volume defined by these materials and the conjugate heat transfer between the flow and these solid bodies

Solution

To solve this problem we would need:

-Individually wrap these solid bodies

-Sew the wrapped solid bodies with the caps

-Create the volume mesh making sure that the mesh in the solids is kept

Conjugate Heat Transfer with multiple solid materials



• Use the Objects, Manage to draw the objects

• Click on Wrap

• Select all objects in the Objects list

• Select Individual Object Surfaces under Target

• Select cut-wrap under Method NOTE: we can do the same process with shrink-wrap as well.

• Click Wrap



• The wrapping process will take a few minutes depending on the speed of your computer

• Once done a set of wrapped objects, prefixed with wrap-

• Select these objects and click Draw



• Observe that each object is separated from the others. This step would only have been 100% necessary if the objects themselves were non-conformal i.e. disconnected. In this case we could have just changed our conformal faceted geom objects directly into “wrap” type objects, avoid the wrap step and go straight to sew.



• Click on Sew under Surface Mesh

• Select all the wrap-* objects

• Click Sew



• The process may take a few minutes depending on the speed of your computer

• Once over, select the sew-object from the list of Objects and click Draw

• Use the Clipping Plane functionality to view the model with the YZ plane

• Observe that the geometry is now fully connected between solids by mutual Face Zones



• Click on Improve

• Select the sew-object from the Objects list

• Set 0.6 for Quality Limit

• Click Improve

• The maximum skewness is now 0.61



• Now we are ready to generate our volume mesh.

• We will grow prisms and a HexCore mesh

• Click on Auto Mesh

• Select sew-object under Object

• Select fluid-volume under Material Points

• Make sure the Keep Solid Zones is checked

• Under Boundary Layer Mesh click Set…



• Under Prisms click on the Direction tab

• Select sew-object under the Object Name

• Click on Material Point and select fluid-volume under the Material Point list

• Click Orient – The four wetted wall Boundary Zones that

face the part of the space defined by the Material Point are automatically extracted and selected. Face normals are auto-oriented.

– A new boundary zone group _prism_fluid-volume is created containing these zones for easy selection



• Click on the Growth Tab

• Select the inputs for Offset Method, Growth Method, First Height, Number of Layers and Rate as shown

• Note you can press <Enter> after populating the fields to update Total Height

• Click Apply under Zone Specific Growth (applies zone specific growth to boundaries)

• Click Apply at the bottom of the panel (Global apply for all tabs)

• Click Close to return to the Auto Mesh panel



• Make sure that the Prisms check box is checked

• Click Hexcore under Volume Fill

• Click Apply

• Save a copy of the surface mesh all set up and ready to volume mesh

– File Write Mesh CHT_mesh_setup.msh.gz

• Click Mesh

• The meshing process may take a few minutes depending on the speed of your computer

• Once done use the menu system to navigate to Display, Grid and go to the Cells tab.

• Click on the Bounds Tab

• Click on the Limit by X check box



• Go the the Cells tab

• Select in the list the different cells zones for solids and the fluid as well as the prism cells.

• Select All and Display


Note we always set bounds

first before displaying cell

zones to avoid displaying the

full mesh


• Before we transfer the mesh internally to Fluent, it is a good idea to clean up the mesh. You will notice by examining the contents of the Manage Objects panel that there are many different objects (including the original ones) as well as their associated Face and Edge Zones similar to what you see below. Save the mesh by going to File-Write as separate-solids.msh.gz

Cleanup and Export to the Solver Mode


• Click on the Cleanup Button

• A pop-up window appears indicating what the cleanup process will do and asking permission to proceed

• Click Yes

• The Manage Objects contains only our final mesh type object. Original geometry and wrapped objects are removed



• To transfer the mesh to the solver, click on the icon on the upper left corner of the Fluent window – Switch to Solution

• Click Yes to the pop-up window


workshop 5: basic workflows - mr-cfddl.mr-cfd.com/tutorials/ansys-fluent/fluent_meshing...in the...

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