Fluent Meshing 14.5 WS5 Basic Workflows

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2011 ANSYS, Inc. December 21, 20121 Release 14.0

14.5 Release

Introduction to ANSYS

Fluent Meshing

Workshop 5:

Basic Workflows


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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 multiplesolid materials

Introduction


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Open the Fluent Launcher by clicking the Windows Startmenu, then selecting Fluent. 14.5

in theFluid Dynamics sub-menu of the ANSYS 14.5program 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


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FileImportCAD...Ensure that Import Single fileis enabled.

Select the file WS5_T-junction-demo.agdbEnable Import Curvature Data from CAD.

Retain the value of 1for Scale Factor and the selection of body

in the One zone perdrop-down list, respectively.

Click the Advanced... button to open the CAD Advanced Options dialog

box.

Enable Save PMDBin the Filegroup box. Select mmin the Length Unit drop-down list.

Select Conformal Tessellation in the Tessellationgroup box.

Specify values of 1and 10for 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 Applyand close the CAD Advanced Options dialog box.

Click Importin the Import CAD Geometry dialog box.

Close the Import CAD Geometry dialog box.

Import the CAD Geometry


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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


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Once the CAD import is complete, click on

Manage

Select all the objects in the Objectslist and click Draw

Geometry Overview


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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+Nto 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+Dto calculate the distance between these two

nodes. We will use 5mm as the representative

gap distance

Model Preparation-Gap Removal



Click on ObjectsManage

Select the objects in the Objects list and observe

the type in the Object Typepull down menu.

These are geomtype objects, which is the

default type object after geometry import

The Gap Removal tool that we are about to use

does not work with geomtype 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 wrapand then click Change Type.

Click Yesto the pop-up window/question




Click on Remove Gaps

The Remove Gapspanel 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-1and solid-2as 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 Listto 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



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Before Gap Removal

After Gap Removal



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We will need to create three cap surfaces

Two of them will represent Velocity Inletsand one them will represent a Pressure Outlet

Click on Capsunder Create as shown

Choose all objects and click Draw

Model Preparation-Create Caps

1

2 3


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Type inletunder 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 extractedges for the capping object at creation

Select Auto Redisplay(updates graphicsautomatically after cap creation)

Zoom close into the area numbered 1in theprevious slide.

RMBselect one of the edges at the inlet. The

selected edge is marked with bold red color(the circle in the image is for betteridentification of the edge-any edge along theedge of the inlet would serve the purpose

Click Create



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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 2specify inlet2for Object Name

and velocity-inletfor Type

For area 3 specify outletfor Object Name

and pressure-outletfor Type


1

2

3


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We need to create sizing functions in

preparation for meshing. Click onCreateSize Functions in the task

page

In the Size Functionspanel, under

Global Controlsmodify the entries as

shown in the figure and click Apply

Click Create Defaultsto 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 Sizesto

show min/maxsizes in the graphics.

Generate Size Functions


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Select the default-edge-curvature

enter 10 under Normal Angle andclick 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 coarsedefault mesh



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Perform the same

step as before, this timeselecting the

default-face-curvature

and specifying the same

Normal Angle 10.

Click Change Click Close



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Click on Objectsand then Manageand select

only the solid-1object. Click Draw. Usectrl-ahot key to centre the graphics

Click on CreateMaterialPoint in the task

page

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

Material Point Creation


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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 tothe solid. Rotate the model as needed


First Point Second Point


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Type flow-volumein 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 renderedin the graphics window as shown here


If the position is satisfactory, then click

Createand the material point will be

created. Click List to see a list of active

material points.


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Alternatively, click on the graphics window and then type Ctrl+Ztoactive the Zone selection filter

RMBclick on the object and then click Compute

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

Namethe new point as flow-volume-alt

You see that the material point is at the centroid of the Face Zone selected Click Createand then List to list the available material points

Material Point Creation-AlternateApproach


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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 anyissues 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-AlternateApproach


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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


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Problem Statement

As a CFD user, I was given a set of CAD file(s) of an assembly consisting ofsolids 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-wrapor shrink-wrap

-Grow prisms in the Fluid Region and a Volume mesh using Auto Mesh

Extracting the Flow volume


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

Click on Wrap

Select all the objects in the list

Under Targetselect Fluid Surface Under Method select cut-wrap

Under New Object Name type

extracted-fluid

Pull down the menu under Material Pointand select the material point flow-volume

Click Wrap

Extracting the Flow Volume usingCut-Wrap


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The wrapping process will take a few minutes, depending on the speed of

your computer.

Once complete, click on Manageand then select the object extracted-fluid

Before you click Drawdisable Draw Edge Zones from the Object Optionsin

the main Fluent window to improve the clarity of the display

Now click Draw



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The extracted flow volume isdisplayed.

Close examination of the mesh

reveals however that it is not

appropriate for volume meshing

just yet and it needs to beimproved.



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Click on Improve under Surface Mesh

Select the extracted-fluidobject from the

Objects List

Without changing anything else click Apply

This process creates a Meshobject

extracted-fluid-14:9

From the improve panel, select

extracted-fluid-14:9and click Draw



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Before Improve After Improve


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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 Groupsas shown

On the Face Groups list select the

_mesh_group_extracted-fluid-14:9

Click Activate

Click Close



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Use the Menus and navigate toDisplay 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


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Click on Wrap

In the Wrappanel select inputs as shown.

Note that now we are selecting shrink-wrap

under Method

Click Wrap

Extracting the Flow Volume usingShrink-Wrap


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The Shrink-Wrap operation will take a few minutes depending on the speed

of your computer.

Once done, Drawthe object extracted-fluid



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Cut-Wrap Shrink-Wrap


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Click on Improve under Surface Mesh

Select the extracted-fluidobject from the

Objects List

Without changing anything else click Apply

This process creates a Meshobject

extracted-fluid-14:9

From the improve panel, select

extracted-fluid-14:9and click Draw



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Mesh after Improve



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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

Conjugate Heat Transfer with a singlesolid material

Unified Solid

Multiple Solids


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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-modelunder New Object Name

Click Sew



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

could be improved

Click on the Improvebutton

Select the sew-model

Specify 0.6 under Quality Limit

Click Improve

The maximum skewness is now 0.6

down from 0.74



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To create the volume mesh click on Auto Mesh

Select the sew-modelunder Object

Select the fluid-volumematerial point under

Material Points

Make sure that the Keep Solid Cell Zonesis checked

Click Mesh



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Use the Menus to navigate to Mesh Manage

As you can see, there are two

distinct Cell Zones created, the

fluid-volumeand single-solid


Save the mesh as

single-solid.msh.gz


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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 multiplesolid materials


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



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The wrapping process will take a few minutes depending on the speed ofyour computer

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

Select these objects and click Draw



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Click on Sewunder Surface Mesh

Select all the wrap-*objects

Click Sew



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The process may take a few minutes depending on the speed of yourcomputer

Once over, select the sew-objectfrom 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 bymutual Face Zones



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Click on Improve

Select the sew-objectfrom the Objects

list

Set 0.6 for Quality Limit

Click Improve

The maximum skewness is now 0.61



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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-volumeunder Material Points

Make sure the Keep Solid Zones is checked

Under Boundary Layer Meshclick Set



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Click on the GrowthTab

Select the inputs for Offset

Method, Growth Method, First

Height, Number of Layersand

Rate as shown

Note you can press afterpopulating 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

Meshpanel



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Make sure that the Prismscheck box is checked

Click Hexcore under Volume Fill

ClickApply

Save a copy of the surface mesh all set up andready to volume mesh

File Write MeshCHT_mesh_setup.msh.gz

Click Mesh

The meshing process may take a few minutesdepending on the speed of your computer

Once done use the menu system to navigate to

Display, Gridand go to the Cellstab.

Click on the Bounds Tab

Click on the Limit by Xcheck box



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Go the the Cellstab

Select in the list the different cells

zones for solids and the fluid as well

as the prism cells.

Select Alland Display


Note we always set bounds

first before displaying cell

zones to avoid displaying the

full mesh


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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 ManageObjects 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-Writeas separate-solids.msh.gz

Cleanup and Export to the Solver Mode


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Click on the CleanupButton

A pop-up window appears

indicating what the cleanup

process will do and asking

permission to proceed

Click Yes

The Manage Objectscontains only our final mesh

type object. Original

geometry and wrappedobjects are removed


l d h l d


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To transfer the mesh to the

solver, click on the icon on theupper left corner of the Fluent

windowSwitch to Solution

Click Yes to the pop-up window


Fluent Meshing 14.5 WS5 Basic Workflows

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