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7-1ANSYS, Inc. Proprietary 2009 ANSYS, Inc. All rights reserved.

April 28, 2009Inventory #002645

Chapter 7

Introduction toMultiZone Meshing

ANSYS MeshingApplication Introduction

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Introduction to MultiZone Meshing



Training ManualOverview

Comparing Sweep and MultiZone

Comparing Thin Sweep and MultiZone Example for Sweep, Thin Sweep, and Multizone Methods

Approach for the MultiZone Method

MultiZone Method Settings

Mapped Mesh Type

Free Mesh Type

Source Selection

Defeaturing

Inflation and MultiZone

Workshop 7.1 MultiZone Meshing for a Block Geometry with Pipes Workshop 7.2 MultiZone Meshing for a Tank Geometry with Piping

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Training ManualComparing the Sweep and MultiZone Methods

Sweep Method: Sweeps a singlesource/face to asingle target/face.

Does a good jobof handling multipleside faces along sweep

Geometry needs to bedecomposed so thateach sweep path isrepresented by 1 body.

Some models can bemeshed with eitherapproach

MultiZone Method: Free decomposition approach Multiple sources to multiple targets

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Training ManualSweep or MultiZone?

Use Sweep Method when:

You have a multibody part where some bodies should be meshedwith Sweep, and some with Patch Conforming Tet

If you want to use advanced size function

Preview Sweepable bodies shows that all bodies are sweepable

Use MultiZone when: You are meshing single body parts that are too complicated for

traditional sweep approach.

You have multiple sources and targets you need to respect(cant use VTs to group into a single source/target)

You need to inflate off source and side faces

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Training ManualComparing Thin Sweep and MultiZone

Some models can bemeshed with eitherapproach

MultiZone Method: Free decomposition approach Multiple sources to multiple targets

Thin Sweep Method: Sweeps multiple sources topaired multiple targets

Good substitute for midsurfacingshell models to get a pure hex mesh

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Training ManualThin Sweep or MultiZone?

Use Thin Sweep Method when:

You have a thin solid part where the source and target faces dont

exactly match, and you dont care about the features on the target

side.

Use MultiZone When:

You have a thin solid part where the source and target faces dont

exactly match, and you care about the features on both sides.

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Training ManualDifferent Sweep Methods Example

Sweep Method:

Thin Sweep Method:

MultiZone Method:

ForExample

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Training ManualSweep Method Treatment

Use VTs to merge multiplesources into 1 source

Multiple sources ignored Multiple targets ignored

Use VTs to merge multiple

targets into 1 target

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Training ManualThin Solid Sweep Treatment

Multiple source Multiple target

Multiple sources captured Multiple targets ignored

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Training ManualMultiZone Method Sweep treatment

Multiple source Multiple target

Multiple sources captured Multiple targets captured

Note, MultiZone will ignore the internal cutouts unless they are in a Named Selection

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Training ManualMultizone Method Approach

Multizone features automatic geometry

decomposition which avoids the need toslice a body up into sweepable bodies to

get a hex mesh with the sweep method

For example, the geometry shown at right

would need to be sliced into three bodies

to get a hex mesh with sweep. With theMultizone method, a hex mesh could be

generated directly

Based on ICEM CFD Hexa blocking

O-grids can be extruded to createinflation

Unstructured regions can be filled with hex-

dominant, hex-core, or tetrahedral mesh

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Training ManualMultizone Method Settings

Multizone will not utilize the Advanced Size

Function (Patch Conforming Tet andSweep Methods only)

Source selection is not mandatory, but maybe helpful

Can exclude or allow free mesh blocks

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Training ManualMultizone Method Settings

Mapped Mesh Type

Hexa

Hexa/Prism

Free Mesh Type

Not Allowed

Tetra

Hexa Dominant

Hexa Core

Source/Target Selection

Automatic

Manual Source

Advanced Defeaturing Tolerance

Minimum Edge length

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Training ManualMultizone Method and Inflation

Algorithm different from otherinflation methods (extruded o-grid)

Scoped to bodies, defined forfaces

Only First Layer or TotalThickness options

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15/387-15ANSYS, Inc. Proprietary 2009 ANSYS, Inc. All rights reserved.


Multizone Meshing for a

Block Geometry with Pipes

Workshop 7.1

I d i M l iZ M hi

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Training ManualGoals

This tutorial will illustrate basic

use of the Multizone method tocreate a Hex mesh for a simplegeometry with the addition of aninflation layer.

Source selection for themultizone sweep will be doneautomatically by the mesherwhen the mesh is generated.

I t d ti t M ltiZ M hi

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Training ManualImporting Geometry

1. Copy the blockandpipes.agdb

file from the Tutorial Filesfolder to your working directory

2. Start Workbench and double-

click the Mesh entry in the

Component Systems panel

3. Right-click on Geometry in the

Mesh entry in the Project

Schematic and select Import

Geometry/Browse

4. Browse to the block and

pipes.agdb file you copied and

click Open. Note that the

Geometry entry in the Project

Schematic now has a green

check mark.


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Training Manual

5. Double click the Mesh entry in

the Mesh object on the ProjectSchematic to open ANSYS

Meshing

6. Close the Meshing Options

Panel at the right without setting

anything.

7. Right-click on Mesh and insert a

Method. Select the body and set

the method to Multizone. Leave

the settings as the defaults asshown

Insert Multizone Method


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Training ManualMesh Sizing and Metric

8. Click on Mesh in the Outline

9. Change the Physics Preference to CFD

and the Solver Preference to Fluent

10. Expand the Sizing Entry and turn off the

Advanced Size Function (it will not be

used for Multizone anyway)

11. Set the Element Size to 0.20 [in]. (Note: if

the units are set to some other system,

click on Units in the Menu Bar and change

to U.S. Customary (in, lbm, )

12. Expand the Statistics entry and set theMesh Metric to Skewness


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Training ManualMesh and Mesh Quality

13. Generate the Mesh. Note the Mesh count and Skewness metric


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Training ManualInflating the Multizone Method

14. Insert Inflation for the Multizone

Method. Pick the outercylindrical faces of the pipes

and the 4 side faces of the block

as the Boundary. Set the

Inflation Option to Total

Thickness with a value of 0.20[in].

15. Generate the mesh.

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ANSYS, Inc. Proprietary 2009 ANSYS, Inc. All rights reserved.


Multizone Meshing for a

Tank Geometry with Piping

Workshop 7.2


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Training ManualGoals

This tutorial will show how to use

the Meshing Application inANSYS 12 to generate a meshsuitable for a CFD simulation of achemical process flow.

The geometry, consists of threebodies representing a tanktogether with a single inlet andoutlet pipe.

The goal is to produce an Hexmesh throughout the domainwithout any further decompositionof the geometry using theMultizone Method.


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Training ManualCreating a Standalone Meshing System

1. Launch ANSYS 12.0 Workbench from the START menu

2. Open the Component Systems section of the Toolbox on the LHS ofthe WB GUI.

3. Double click the Mesh option


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Training ManualImporting the Geometry

4. Right click on the Geometry button in the RHS of the WB panel and

select Import geometry (the question mark on the button turns to a tickonce a geometry file is imported)

5. Import the 2-pipe-tank.agdb file

6. Double click on the Mesh button to launch the Meshing Application


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Training ManualGeomety

7. The original geometry was modified in DesignModeler

The tank was split into three bodies and some simplification was made toremove small faces that are not important to the analysis

One multi-body Part was created and a given the name Fluid and thematerial type Fluid

Individual bodies were re-named


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Training Manual

8. In the Meshing Options panel to the RHS of the main window select thefollowing meshing options:

Physics Preference

CFD

Mesh Method

Automatic

Click OK after youmade the selections

In Units, make sureit is set to Metric, mm

Meshing Options


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Training ManualNamed Selections

9. Named Selections are used to assign Fluent name and zone types

Set the Cursor Mode to Face selection

Select the inlet face

RMB select Create Named Selection

Assign the name Inlet

Repeat for Outlet

A naming convention hasbeen established toautomatically assign zonetypes in Fluent

For example -

Inlet

Velocity-inlet zone

Outlet

Pressure-outlet zone

See Fluent Mesh export section

of the manual for all options.


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Training ManualGlobal Mesh Settings

10. Set Global Size and Quality control Click on Mesh in the Model Tree to open up the

Details of Mesh panel

Sizing

Turn Off Use Advanced Size Function Multizone does not use this option

Change the Relevance Center

Fine Recommended for most CFDapplications that apply the Multizone Method

Statistics Assign Mesh Metric

Option Skewness

Maintain all other defaults


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Training ManualInserting a Multizone Method

11. Insert Mutizone Meshing control

Set the Cursor Mode to Body selection RMB (in Window)Select All the bodies

RMB (in Tree)Insert Method

Select Multizone


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Training ManualSetting Multizone Sources

12. Select Mutizone Source faces

Change Src/Trg SelectionManual Source To ensure the middle section can be swept

Set the Cursor Mode to Face

Pick the five green source faces(see top image)

Rotate the model to look at therear of the tank

Pick the additional fivered source faces(see bottom image)

Apply


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Training ManualGenerating the Initial Mesh

13. Create an initial Mesh of the model

RMB (in Tree)Generate Mesh

The mesh is successfully created but refinement is clearly needed The mesh at the inlet and outlet pipes and close to the pipe/tank intersection is

insufficient to capture the physics correctly

This can be achieved by inserting some additional meshing instructions such asInflation, Sizing and Biased Sizing to improve the pipe/tank meshing


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Training ManualFace Sizing

14. Add Face Sizing for the pipes to control the size of elements

Start by removing the mesh RMB (in Tree)Clean and confirm

Make sure youre using Face Selection and pick the four faces shown inGreen

RMB (in Tree)Insert Sizing

Set Sizing Details:Set Element Size

1 mm


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t oduct o to u t o e es g



Training ManualAdding Inflation

15. Add Inflation(boundary layers)

Set the Cursor Modeto Body Selection

Select the centralgreen body

RMB (in Tree)Insert Inflation

16. Set Inflation Details

Switch to Faceselection

Select the four greencylindrical faces andApply

Set Inflation Control Number of Layers

2

Maximum thickness 1 mm

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Training ManualGenerating the Final Mesh

19. Generate the mesh

RMB (in Tree)Generate Mesh

Statistics

Elements

~45,000

Max Skewness

Below 0.8

Overall a good Quality mesh


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Training ManualExamining the Mesh

20. Examine the Mesh

Inflationon the pipewalls

Sizing 4elementson face

Sizing element size 1mmacross pipe and biasing toincrease density at transition


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Training ManualSaving the Project

21.The mesh is now complete RMB (Tree) select Update

Select File > Close Mesh to close the Mesh application

In the WB panel select File > Save Project As and give the project a name

Exit from ANSYS Workbench by selecting File > Exit

22. Further Work

Change the mesh settings for each of the additional parameters

How do each of these parameters influence the mesh?

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