ICEM CFD Ansys Tutorial

1

Lecture One: Introduction to the

CFD

The basic procedure for CFD simulation

Flow

wall

wall

Preprocessing(1)Geometry definition

(2)Discrization

(3)Physical modeling

(4)Boundary conditions

Simulation(1)Solver definition

(2)solving

Post-processing(1) Plot results

(2) Conclusions

2

Fluent PackagePre-processing

Solving

Post-processing

ICEM

Pre-processing

� Fluid domain definition (Geometry)

� Mesh Generation

� Boundary condition definition

3

Principle of fluid domain definition

Bottom up method:

(1)key points

(2)Lines

(3)Surfaces

(4)Volume(3D)

Geo 1

The domain should

be closed by lines to

form face

Step 1 Step 2

Step 3

Geo 2

Step 1

Step 2

Step 3


4

Step 1Step 2

Step 3

Using Curves


Introduction to the ICEMICEM is a specialized software to create the geometry, mesh

and boundary conditions for Fluent; in the following slices

we will use ICEM for the pre-processing.

From Start menu�

All programs�

Ansys�

Ansys CFD ICEM

5

Problem specification:

Inlet

12cm

14cm

outlet

2cm

1cmP1

P2 P3

1cm

Fluid: Water; 2D problem

The coordinates for the 6 points:

P1: 0, 0.01, 0

P2: 0, 0, 0

P3: 0.02, 0, 0

P4: 0.02, -0.01, 0

P5:0.14, -0.01, 0

P6:0.14, 0.01, 0

Therefore z coordinate is the same

Note: Because the default unit

system in Fluent for length is m, so

in order to make it easy, the length

unit we use in ICEM is assumed to

be m.

P4 P5

P6

strategies � Bottom-up approach:

point � line � surface � volume

Here we use Bottom-up approach, that is from

point �� line �� surface

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Procedure

� Step 1, start the ICEM

From Start menu�

All programs�

Ansys�

Ansys CFD ICEM

Main Window

Main graphic window

Function Tabs

Message window

opensave

Fit the window

Zoom in or out

undoredo

Display

Control Tree

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Procedure

Point � Line � Surface

� Step 2, choose the proper working directory

all geometry and mesh files will be stored in that directory

File � Change Working Dir…

Choose the directory you want to

save, such as C:/lecture1

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Step 3 Create the initial points

(1) Choose Geometry tab

(2) Click for creating points,

(4) Click explicit locations

(6) Input x y z coordinates

(7) Click apply for creation

(9) When you finish creation, click

dismiss to quit the panel.

(1)

(2)

(3)

(4)

(5) Choose ‘Create 1 Point’ in the list

(8) Create other points from step 5 to 6

(5)

(6)

(7)

The coordinates for the 6 points:

P1: 0, 0.01, 0 P2: 0, 0,0 P3: 0.02, 0,0 P4: 0.02, -0.01,0

P5:0.14,-0.01,0 P6:0.14, 0.01,0

(3)remain the part name to be GEOM

Click to show points in the whole window,

you can find it in the left corner of toolbar

6 points can be found in the black background

Note: make sure the part name is unique for one geometry, in this

example, when you want to create points and lines , check the part

name to be GEOM, or the name you have given in the beginning.

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Other operations

(1)enquiry the point information (a) In the toolbar (left corner), left click the third icon to open the list,

then choose location icon

(b) Mouse cursor becomes a cross, move the cursor to one point, and left

click that point

(c) Using middle mouse button to finish

(d) Scrolling middle mouse wheel to zoom in and zoom out

(2) delete the unwanted points

(a) In Geometry tab, choosing delete point icon

(b) In the Delete Point panel, choosing selecting points icon

(c) In the main window, a toolbar appear to help you to choose, and a line of

red text explains how to choose.

Using left button to choose, right button to cancel, middle button to finish

(d) Click apply to delete points, dismiss to quit the panel

If you have deleted one of the 6 points, please create it again.

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Note: about selection in the main window by mouse

During the selection procedure, the cursor changes the shape to be a cross, a

toolbar appears to help the selection, move mouse to individual icon to see

the hint (waiting for seconds )

A line of red text will show in the bottom

Left button : select several entities in an order, such as p1, p2 , p3, …

Right button: cancel the selection in a reversed order as selection, …p3, p2, p1

Middle button: accept the selection

Note: it may automatically trigger the following function for the

selection, for example, during the line creation, after you select two points, when click middle button, the line will be created, you do not need to click the apply button for creation. Check the output information for the actions done by middle mouse button

Procedure

Point�Line�Surface

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� Step 4 Create the lines

(1)Geometry tab� create lines � from points

(3) choose selecting points icon

(4) Choose two points in the main

window

(5) Click apply to create one line

(6) Repeat step 2 to 4 to create other

lines

(2) keep the part to be GEOM

Make sure that all the lines are created around the step pipe

� Other operations

� Delete unwanted lines (Geometry Tab)

� Undo

� Rotate in the graphic window

hold left mouse button + move

� Rotate 2

hold right mouse button + move

� Translate

hold middle mouse button + move

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Choosing Front in From view menu to restore the view if the points are

not shown properly

Boundary Definition

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(a) Where is the fluid region?

(b) What is the type of fluid? Air, water or blood?

(c) Fluid direction, from where and where to go?

(d) Boundaries to constrain the fluid flow, such as wall, symmetry boundary

Computer does not know where is fluid domain, it is

your job to tell it

Fluid domain

Inletoutlet

wall

wall

Inlet:VelocityMass flow ratePressure……

Outlet:VelocityMass flow ratePressure……

Wall:Non-slipSlip……

Check Model Control Tree

Under Parts:

The GEOM is the geometry you have created

Now we need to define inlet, outlet, wall, fluid

domain in GEOM

Fluid domain

Inletoutlet

wall

wall

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Step 1: Define fluid domain

(a) In Geometry tab, choose Create Body icon

(b) Change the name, usually BODY

(c) Choose Create Material Point

(d) Turn on Centroid of 2 points

(e) Click to define two screen locations

Click left button in

upper and lower walls,

middle mouse button

to accept the selection

Location 1

Location 2

(f) OK to finish

The created body is showed in the main window

Model Control Tree view

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Step 2: define inlet

(a) At model control tree view, right click Parts

(b) From the menu, select Create Part

The panel for creating part

(c) Change the part name to be Inlet

(d) Select create part by selection

(e) Click select entries

(f) In the main window, select the edge for Inlet

boundary. Left click to select, middle button to accept.

When selected, the line will be highlighted

(h) Check the parts in model control tree view

inlet

INLET will be added. when you turn off inlet, the edge will disappear in the main window, this step can be used to verify the boundary creation

(g) Click Apply

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Step 3: Create Outlet Boundary

outlet

Model control tree view

Step 4: select the left edges for Wall

Edges for wall boundary

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Check model control tree view

There are:

GEOM

INLET

OUTLET

WALL

You can turn off to check where those parts are, now GEOM only represents

created points, you can change the name to be points, or leave it

Save the geometry file from File Menu

Mesh: PrincipleDivide the computational domain into small parts,

on which the computation will be performed

Step 1Define the division along the lines

Step 2Divide the region based on the line division

E1 E2 E3

E4 E5 E6

Basic element shape

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Triangular Mesh

Fine Mesh

Fine meshMore controls on mesh density

Some concerns about the mesh quality

(a) Fine mesh in the region of interest, such as at the step region

(b) Fine mesh near the wall

(c) Fine mesh in the abrupt change of the geometry

……

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Mesh

Lines � Surface

ANSYS ICEM CFD Blocking provides a projection-based mesh generation

environment where, by default, all block faces between different materials are

projected to the closest CAD surfaces.

Blocking Strategy For Mesh Generation

Block Geometry

edge1 Curve 1edge3

edge2

edge4

Curve 2

Curve 3

Curve 4

The association between Block to the geometry is :

Edge1 � Curve1

Edge2 � Curve2

Edge3 � Curve3

Edge4 � Curve4

The mesh generation in Block will be projected to

the corresponding geometry by defined

association

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Steps in Blocking Meshing

(a) Create and split blocks, discard unused blocks to capture underlying shape

(b) Associate edges to curves to capture hard features. Move vertices to position

block corners on geometry

(c) Assign mesh sizes such as maximum element size

(d) Automatically generate mesh

(e) Write Output files to the desired solvers.

Blocking strategy in the example

Geometry

(a) Initialize Block

(b) Split block

(c) Delete unnecessary block

(d) Define association between block and geometry

(f) Mesh generation

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Step 1: Create the blocks

(a) At Blocking tab, choose Create block icon

the Create Block panel will show in the left

(b) Choose BODY from the list

(c) Choose initialize block icon

(d) Choose type to be 2D planar

(e) Apply to finish, dismiss to quit

The Block will be created for the body we just created, the body comes from geometry creation procedure (fluid domain definition, page 28)

This step will automatically create the block

according to the dimension of the created

geometry

Created block( the white lines indicate the existence of block)

output showed in the information window

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(a) Select Split block from Blocking Tab

Step 2: split block

(b) Choose split blocks icon

(c) All visible to be turned on

(d) Click selecting lines icon

(e) In the main window, left click the top line

in the middle position, a line will be created.

(f) Choose the new created line by left mouse

button and keep holding to move the line to the

step corner

(g) Click middle mouse button to accept the creation

(h) If you want to cancel the creation just right click

Click position

(I) Left click the left line in the middle position, move the created line to the step

corner

Click position

(J) Click OK to finish

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Step 3: deleted unnecessary block in the left corner

(a) In the Blocking tab choose delete block

(b) Click selecting blocks icon

(c) In the main window choose the left lower corner by

left click, the block will be highlighted.

This one

(d) Middle button to accept, then the block will be deleted

Now only three blocks are left, which are the same locations as the step boundaries

Block 1 Block 2

Block 3

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Step 4: associate the created block with geometry, a one to one map for

the edges in block and curves in the geometry.

Note: block, edge are logical structure, point, curve, surface, volume are

physical structure of the model. This step also tells comupter the model

region boundary.

(a) Choose associate icon

(b) Choose associate edge to curve

Edge: from block; curve: from GEOM part

(c) Click select edge icon

(d) In the main window to select one line, middle

button to finish the selection

The name for the selected edge

(e) Click select curve icon

(f) In the main window, select one curve (when

selected, the line will be highlighted), the same

location as in step d, middle button to finish the

selectionNote: In step f, when click middle button, ICEM may automatically create the association without clicking Apply

Edge 1Curve 1

Edge 2

Edge 3

Edge 4

Edge 5

Edge 6Edge 7

Curve 2

Curve 3

Curve 4

Curve 5

Therefore the associates are

(1) Edge1 � Curve 1







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The associations may be verified by selecting Edges >Show Association in the

Display tree. As shown, the green arrows in the display point from an edge to its

associated curve. Nodes and vertices of these edges will project on to the

associated geometry.

Display Tree, in the left side

Right click

In our example, because the edges are the

same locations as the curves, so the

arrows can not be seen.

Step 5: applying mesh parameters

(a) In the blocking tab choose “pre-mesh params” setup

(b)”Choose meshing parameters”

(c) Choose select edge icon

(d) In the main window choose the left edge for

inlet, middle mouse button to accept, the name in

ICEM will be displayed

(e) In the number of nodes, input 20

(f) Spacing 1 and 2 are the minimum space for

each node from the starting point to the ending

point respectively

(g) Ratio 1 and 2 are corresponding ratio of

distance between the nodes for both ends for

nin-uniform mesh distribution

(h) Click apply to accept the change and

back to (c) to choose another edge.

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Node numbers for all curves

20

20 20

80

40

100

Step 6: Initial Mesh Generation

(a)In the structure tree, open blocking part

(b) Tick pre-mesh box,

(c) A pop-out window shows in the main working

space and choose “yes” to re-compute pre-mesh.

Note: if the pre-mesh box

was on, click it to turn it

off and turn it on again to

re-calculate the mesh.

Pre-mesh will be displayed as this

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Step 7: Saving the Mesh and Blocking

(a) Save the mesh in unstructured format: Right mouse select Pre-Mesh

and select Convert to Unstruct Mesh to generate the domain file.

Now you have meshes created from pre-

mesh. If you turn off “Pre-Mesh” in

“Blocking”, you will still see meshes in the

model which contains shells and lines.

If you are not happy about the mesh, you can

always delete them by File > Mesh > Close

Mesh. It will delete all meshes in the project, but

“Pre-Mesh” are still there since they are not real

mesh yet.

Check the line element to see the walls.

In a 2D problem, line element acting as surface element in 3D to enclose

the physical domain. Therefore, any broken parts of line element will

cause problem in CFD calculation.

(a) In the structure tree window:

(1) turn off “geometry”

(2) in “mesh”, turn off “shells” and click open “lines”

(3) in “blocking”, turn off every thing except subsets

(4) in “parts”, turn on everything.

you should see a clear boundary of the model where the walls were

defined (including inlet and outlet boundaries)

If you turn off “lines” in blocking, the model should disappear.

(b) If you find gaps in the model wall when “line” is on, you should either

go back to the stage of block definition and start again, or go to “Edit

Mesh” on

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Edit mesh (need advanced reading, optional)

Edit mesh gives you many options to repair your mesh, but further

readings are needed for the option.

You can generate line meshes under “create element”

In the “create element” you can create some

line meshes in the broken gapes shown in the

previous model. (“Help” file will give your more

details).

Save the project (for restart next time)

(a) If the line element checking is satisfied,

you can save the project.

(b) Select File > Save Project As… and type

in a project name. All files: tetin

(geometry file), blocking and

unstructured mesh will be saved.

(c) You can load project file for continuation or

just geometry file. It is better to save the project

frequently.

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Step 8: Export mesh

(a) From Output tab choose select solver

(b) From the list select Fluent_V6 for Output Solver

Leave this(c) Click OK to finish setting

Step 9: Save the project and export the mesh

(a) In the Output tab, select

(b) A dialog will prompt out, select Yes for saving

(c) Then a file open dialog will ask

you to select the mesh file(*.uns),

which is the same name as your

project name. Usually the name

provided by this dialog is the right

one, click OK to open

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(d) Turn on 2D

The example is a 2D problem, leave others to be default

(e) You can change the Output file name

by replacing fluent

(f) Click Done

(g) Go to the working directory, find the mesh file:

fluent.msh or (yourname).msh

(h) Save the mesh file

for next lab session

Summary

Basic Elements for CFD with ICEM:

� Fluid domain geometry definition

� Define parts including boundaries, walls and all parts that you may need to be separated from the general geometry so that can be used in CFD boundary condition and post processing

� Mesh generation (including mesh checking)

� Mesh Export

Documents

ICEM CFD Ansys Tutorial