Icem...This is tutorial may good for beginner in ICEM CFD..

1. ICEM 1 0 2
ghazlani m. ali
Understanding the tutorials
May 2013 – version 1.0

2. Ghazlani M. Ali: ICEM 102, Understanding the tutorials,
c May 2013

3. Teachers open the door but you must enter by yourself
— Chinese proverb
INTRODUCT ION
Before going any further, i would like to inform the reader that I’m
far from being an experienced ICEM CFD user with some ten years of
experience. I have started not even three years ago, every time i had
problems with the software, i went online and asked for help on cfd-online.
com. A great community is there, which without them, probably
this book would have been absent.
The tutorials available in Ansys customer portal are the real deal.
Sometimes, you tend to follow the instruction without knowing what’s
happening. The purpose of this book is... let’s say to bring a sense to all
of what you are doing. To explain why we do this or that. I will also
include some interesting features not covered in the tutorials.
Many thanks go to the people in cfd-online, i have learned a lot with
you guys, gratitude.
Mistakes will be made throughout the book. English is my third lan-guage,
please bear with me...
iii

4. CONT ENT S
i a guide to the graphical interface 1
1 working efficiently 2
1.1 Organization 2
1.2 Useful buttons 2
ii geometry 4
2 geometry 5
2.1 Parts 5
2.2 Bodies 5
2.3 Curve and surfaces 6
iii the mesh 8
3 unstructured mesh 9
3.1 Good geometry 9
3.2 Flow of work 9
3.3 Adding an interior wall 10
3.4 Mesh Algorithm 10
3.5 Never too late to change the boundaries 11
3.6 The Edit Mesh Tab 12
4 structured mesh 14
4.1 Introduction 14
4.2 blocks can be parts 15
4.3 Useful links 15
5 merging an unstructured mesh with a structured
mesh 17
6 conclusion 19
iv

5. L I S T OF F IGURE S
Figure 1 The tabs 2
Figure 2 Holes to be grouped 5
Figure 3 A look at the mesh... 6
Figure 4 Difference 6
Figure 5 Difference 7
Figure 6 The mesh tab 9
Figure 7 The global mesh parameters 10
Figure 8 Interior wall 10
Figure 9 Select mesh elements tool 11
Figure 10 Select geometry tool 11
Figure 11 Selected boundary 12
Figure 12 Before and after 12
Figure 13 Duplicated mesh 13
Figure 14 Before and after 17
Figure 15 Before and after 18
v

6. Part I
A GUIDE TO THE GRAPHICAL INT ERFACE
There is a lot of tabs in ICEM CFD, it’s all about ordering
your work, You will always navigate those tab from left to
right. Take some time and read this part to learn more about
the steps of creating a mesh

7. 1 WORKING E F F ICI ENT LY
1.1 organization
The graphic interface in ICEM CFD is made so people do not get lost
when working in it, but yet if you are just starting in cfd, you WILL GET
LOST. here is what you need to understand: The steps by which we go
through are pretty simple:
1. One starts by creating, or importing and modifying its geometry.
This is why the geometry tab is first in the row. Everything there is
related to creating, deleting, and changing the points, the surfaces,
and the curves.
2. Next is the Mesh tab. This is where the parameters of the mesh
will be specified: size of element, what kind of meshing technique
one wants to use, each of the parameters can be applied in a global
scale, or for a particular part of your geometry, this why we find
"surface mesh" or "curve mesh" tab.
3. Next is the blocking tab, this is to be skipped if you are planing an
unstructured mesh (for the moment). There are some times when
the blocking tab can be used along the mesh tab, but that will
happen when you’ll level up your knowledge in ICEM CFD.
4. When your mesh is generated, you will have to improve its quality,
may be duplicate it, delete it, and many more editing. The edit
mesh is there for that. So you will play with that tab when you
have a generated mesh, and not before.
5. Finally when everything is ready to be transfered to your solver,
you will then use the "output tab", the name speaks for itself, there
you will assign the boundary conditions and create the mesh file
to be imported in the solver ICEM 102
version 1.0
Figure 1: The tabs
1.2 useful buttons
There are some very useful buttons there, you will get the chance to
use them all while discovering the software, or after reading this book...
2

8. 1.2 useful buttons 3
Most of them deal with "how to efficiently select and entity". There are
many, i will only cite the most useful ones. The more we advance in
this book, i shall explain more. Let us take our cube, as we all know, the
cube has 6 faces (surfaces), 8 corners (points), and 12 edges (curves). The
toggle selection buttons make the job easier by letting you pick only the
entity you desire. Two more buttons you may want to use:
All entities
Only visible
all entities will even select the objects that are not displayed in your
screen, very useful if you wish to delete everything.
only visible lets you buy some time if you wish to select all surfaces
that are displayed on your screen when you have ONLY those surfaces
shown. Again, if your points are displayed (checked in the tree menu)
and if you hit that button, surfaces AND point will be selected... just to
make sure you got it ;)

9. Part II
GEOME TRY
When just starting with ICEM CFD. One has to understand
the important of having a perfect geometry. As seen later,
the algorithm behind generating a mesh depends on know-ing
the curves, points and surfaces of the geometry so mesh
boundaries can be applied. If the geometry is bad, absence of
curves, or overlapping surfaces, the resulting mesh -if generated-may
just not be the one you wanted.

10. 2 GEOME TRY
Icem Cfd is good in importing geometries, but not creating ones. Unless
you want to draw a box, a sphere any simple body, it is better to just use
the importer. Using the workbench reader, i never failed in importing an
IGES, STEP or a workbench geometry.
2.1 parts
One of the coolest feature in ICEM CFD is to create a part. Parts can be
anything: curves, surfaces, bodies, points and even a mix of all of them
them.
Figure 2: Holes to be grouped
The main reason why we create
part is to define boundary condi-tion
for the curves (in 2D) and
for the surfaces (in 3D). I’m not
sure if it is available in the tuto-rials
or the training materials but
here is one more useful feature to
use the create part which will give
you some more insights and un-derstanding.
Let’s say we have a
group of holes as shown in the pic-ture
below: While meshing this,
you boss expect from you to put
a minimum a 20 nodes in each
og the curves representing the holes. As you begin with ICEM, you
will probably select individual curves and assign them the 20 nodes.
Here is where the create part will be useful: select create part, toggle
on (only curves) and select all the curves that matter. Name that par
group_curves. Now you have one part that includes all those curves
and if you go to Mesh Tab - Mesh Curve - Select Part - group_curves
and Number of nodes- 20 : it will assign 20 nodes for each curve there.
Now you are using ICEM CFD efficiently.
2.2 bodies
What’s a body? Why creating a body ? I will try to explain it by a very
simple example: figure 2 shows a cube inside another. Think of it as a
metal box suspended in the air. I decide to create a body outside of the
inner cube and name it AIR. If i generate a mesh. The figure below
shows how it will look like.
We notice here that the elements created will propagate until surfaces
5

11. 2.3 curve and surfaces 6
Figure 3: A look at the mesh...
are met. They will not cross the surfaces. I now have a convenient way
to tell my solver FLUENT -for example- that everything outside of the
inner cube means air. Now, What if i want to study the temperature
profile inside of the box. I need to tell my solver that i have aluminum
inside of it. More over, i need to go back to Icem and create a body
inside the inner cube, and call it Aluminum. the figure below shows
the resulting mesh composed of two bodies.
(a) One body (b) Two bodies
Figure 4: Before and after.
I hope you could get this interesting concept. Bodies can be used for
too many reasons, and it will be up to you to exploit this feature in
the future. Let’s move on to put into practice the use of the curve and
surface features.
2.3 curve and surfaces
REMINDER: if we have a square surface, then we have 4 curves, and
4 points acting as boundaries. Simple right? I wanna show now how i
can change my geometry by using them in order to have different inlet.
Figure 5 shows a face of a cube, that face represents an inlet of air. What
if i want to add a small window where the air will enter, and declare all

12. 2.3 curve and surfaces 7
the other boundaries as wall. This can be easily done by going through
the following steps below: By doing so, and after generating the mesh. I
will have two distinctive faces and i can move on to the solver to assign
whatever boundaries i want.
(a) Added points (b) Added curve
(c) Surface split (d) Generated mesh
Figure 5: The steps for splitting a mesh.

13. Part III
THE ME SH
Mesh can be structured or unstructured or both. In 2D, we
tri elements for the unstructured and quad elements for the
structured. In 3D, we have tetra elements for unstructured
and hexa for structured. Penta elements are presents when
prism has been generated...

14. 3 UNS TRUCTURED ME SH
I will not get into every details on how to generate an unstructured mesh
because it is well covered in the tutorials and the training materials. I
want to show some additional features that will let you avoid starting
a thread in the cfd-online forum. I will cover: adding wall, converting
the mesh to a delaunay, checking the quality, creating part for mesh and
some more the Edit Tab.
3.1 good geometry
Before going any further, we have to make sure that we have a good ge-ometry.
Mesh generation will fail if holes, and open surfaces are presents.
3.2 flow of work
The figure below shows what’s under the Mesh tab. One of the first thing
to do is starting by giving a global element seed size. By global it means
that everywhere in your geometry you will not get an element bigger
than what you have specified, for precaution. Always under the Mesh
Figure 6: The mesh tab
tab, the flow of work goes from left to right. After you select you global
parameters, you move on to customize your mesh on individual enti-ties.
If you want to set a max size of 1 for a certain wall, and a max size
of 12 for another entity, you can do that under the part mesh setup.
if you want to apply a special meshing method on a specific sur-face,
or to apply a specific sizing, you can do that under the surface
mesh setup.
The Curve mesh setup let you add a specific node law distribution
to a curve. This is where you specify the number of nodes as seen
in chapter 2 section 1.
9

15. 3.3 adding an interior wall 10
Figure 7: The global mesh parameters
3.3 adding an interior wall
Let us consider our cube example: as we saw in chapter 2 section 3,
Figure 8: Interior wall
we used tow bodies (one inside
the inner cube) and one outside
the inner cube (the metal box sur-rounded
by air) What if i have a
surface inside the cube, as shown
in figure 8, and that i wish to con-checking
the
internal wall
sider that surface as a wall in my
simulation. ICEM CFD will ignore
that surface if you don’t specify
it as wall. Even if it looked like
the mesh was successfully gener-ated,
you will not see your sur-face
in the solver, because no shell
element are associated to it. Let’s see how we can avoid this: I will
start by putting my surface into a part and call it wall_inner_cube,
we click on Mesh tab-Part Mesh Setup, then we check int wall for our
wall_inner_cube. Hit Apply then Dismiss.
That’s it, our mesh is generated and that surface is taken into account .
A typical example for this case can be a flow over vertical plate ;)
3.4 mesh algorithm
Our mesh was generated using the Octree mesh method. Personally, i of-ten
convert it to a delaunay mesh, the latter tends to generate less node,
and is more suitable for CFD simulations. In opposition to the Octree
Method, the Delaunay Method takes root from the surface, making it way
up to fill the hole geometry. That being said, if you want to generate a
delaunay mesh without passing through the Octree method, you need
to have your surfaces meshed.
To get the delaunay mesh, head to Compute Mesh under the Mesh Tab,
and select Quick (delaunay) instead of Robust Octree, click Compute.

16. 3.5 never too late to change the boundaries 11
3.5 never too late to change the boundaries
Now we have a beautiful mesh. But still we are not ready to export it.
In fact, we forgot to define the boundary condition. We usually name a
surface -part- as inlet, then we generate the mesh. The interesting fact to
understand here is that all the shells and the superimposed surface will
form one part, and that will be inlet. If i delete that part, the shell and
the surface will be deleted.
That being said, we show again that a part can be shell elements too,
deleting that part will result in deleting the surface and the shells. below
is a quick demo on how to define a group of shell as a boundary:
1. Right click on part, then select select new part
2. Give a name to your part (boundary), something like INLET
3. click on Select entity, things get interesting here, you need to know
that there is two kind of windows for selecting elements, shown
below, one is to let you select entities for geometry, and another
one for mesh elements, you can toggle between them using the
button framed in blue:
Figure 9: Select mesh elements tool
4. I’m introducing here a few more useful button to help you select
what you want. If you click on surface elements (framed in red), this
will select all the shell elements, they can be either quads or tri.
In our example, they are TRI since we used an unstructured mesh.
Similarly, the button next to it is for Volume elements. i will use
that button if i would like to delete my volume mesh and leave the
surface mesh so i can generate a Delaunay mesh for example. If
you know the part’s name, click on the button framed in pink, all
entities belonging the that part will be selected.
Figure 10: Select geometry tool
5. With the select mesh elements turned on, notice what happens if
you click on any tri elements, followed by all item attached to selected
element, up to angle, the entire boundary will be selected as shown
in figure 7. That’s it, we have now an INLET ready to be set in the
solver after the output is done.

17. 3.6 the edit mesh tab 12
Figure 11: Selected boundary
3.6 the edit mesh tab
Sometimes, it is good to anticipate matters and spend less time dealing
with the geometry. We all now how cylindrical geometries are genera-tion,
it’s all about revolution around a specific axis. Once a mesh is gen-erated,
ICEM CFD can extrude it, copy it, scale it and rotate it. Knowing
this, why not mesh just one sector ? Consider the geometry shown be-low.
Here, i have used a structured mesh by blocking a portion of my
geometry.
(a) A sector (b) full meshing
Figure 12: Before and after.

18. 3.6 the edit mesh tab 13
The quality is not great, the purpose of it is just to show you the ca-pabilities
of the Edit mesh tab. I will then mirror it twice to get the final
geometry. The steps are very easy, under the Edit mesh tab, click on Trans-form
mesh- Mirror - Select all. In our case, we want to get the a hole 360
geometry so we need to check copy1.
Below again, a pattern was created using the copy and translate feature.
Very easy and time saving !
Figure 13: Duplicated mesh
1 One more example on the use of the Edit Mesh tab:
http://www.cfd-online.com/Forums/ansys-meshing/107222-heat-exchanger-too-much-fins.
html

19. 4 S TRUCTURED ME SH
4.1 introduction
This is tough to explain. One way to get a structured mesh in icem CFD
is to block your geometry. It all start by one block initialized, then it is
split into multiple blocks, to finally adapt it to the geometry. For one
geometry, there can be multiple blocking strategy, it is the reason why it
is hard to cover it, and no matter how many geometries I show, you will
always end up with one different that the other, and it will require some
time to come up with a blocking strategy. Some thinks that it like a gene,
you either know how to block or you don’t. I personally don’t think so.
You need to know that there is no special recipe to master it, or there
is only one way: practise on geometries as much as you can. Cfd-online
is full of people seeking help, even if you can’t help, try. And see the
solution from those who helped. Another important point: when you
block your geometry you don’t actually create a mesh, it is more like a
scheme. To have a mesh, you need to right button click on blocking and
select convert to unstructured. Someone once asked this question in cfd-online:
why do I always have to convert my mesh to unstructured even if
it’s structured ? It seems confusing what icem calls a unstructured mesh
is every mesh you can edit using the edit tab and you can output. As I
said before, when you don’t convert your block , you don’t actually have
a mesh, you can’t extrude it or scale or do anything under the edit tab. I
hope I made myself clear, if not... Just keep doing it, one day you’all get
it ;) It is true that a structured mesh is more acurrate, I found the size
of its .msh file much smaller also. Because generating one requires time
and expertise I often start by an unstructured mesh, see how it behaves
during the simulations , if I get a lots of warnings when performing
iterations , I will try to make a structured mesh meanwhile waiting for
the results. Here are some rules that will help you get a good blocking:
when you split a lot, avoid confusing by using the index control.
It may seems difficult to use the numbers to filter the blocks you
want at first sight, so instead, use the select corners option,
it is sometimes difficult to select the blocks you want, I usually
right button click on block and select solid. It makes it easier to
look through than having them set to wire frame
you get a good quality when the vertices are aligned, there are
many ways to align the vertices, take some time to discover how.
It is not difficult at all.
14

20. 4.2 blocks can be parts 15
a blocking can look beautiful, but its quality can be very bad. That
is a problem from the inside.use scan plane after lest mouse click
on premesh to identify where does the problem come from.
4.2 blocks can be parts
Remember the concept of bodies, the purpose of having different bodies
? When using a structured mesh, if you want to differentiate between
different block, you can do that by right button click on create part then
click on blocking material, create part as shown in the margin. This will
result in having different materials in your solver.
4.3 useful links
I tried to gather all the icem cfd related videos on youtube. some of them
are mine, some from ansys, but the majority are from a channel called
turboengineer. The creator of the channel is a dedicated cfd engineer,
very well known among the cfd-online community. He goes by the name
of FAR in the forum. A special thank for all these link...
ICEM CFD basics
The 3D hexa elbow tutorial
The Hexa airfoil in 2D
Wing with sharp trailing edge
Cylinder 2D to 3D
Injector
Cylinder
Cylinder inside cylinder
Meshing of complex cylinder
Introduction to quarter o-grid
Meshing of elliptical cylinder
Sphere cube tutorial
Meshing of ahmed body (and simulation)
Backward step with downstream rectangular inclined plate
Mirroring block and geometry around symmetry plane
2D to 3D via rotation
Blocking strategy for cruciforms fins

21. 4.3 useful links 16
LES ICEM CFD blocking
Supersonic intake hexa

22. 5 MERGING AN UNS TRUCTURED ME SH WI TH A
S TRUCTURED ME SH
From time to time. we can come across geometries that can be decom-posed
in 2 parts: a difficult part impossible to block. Another one where
blocking is pretty much doable. In this case, it is possible to merge a
structured mesh with and unstructured one. Another scenario: using a
structured mesh obliges us to have a dense region even when we don’t
really need it. It is practical to use large elements near the entrance and
refine the more and more we approach our object of interest. The figure
below explains very well what i mean.
Figure 14: Steps.
Here are the main steps on how to perform this operation:
1. Start by generating your unstructured mesh
2. When your blocking is finished, convert it to unstructured mesh.
Icem will ask you if you want to replace your existing mesh or
merge, hit merge. Merging allow two meshes to coexist.
3. under the Edit Tab, click on Merge nodes, then Merge meshes. The
final step will be to select a surface. That surface should contain
both the unstructured and the structured elements.
17

23. merging an unstructured mesh with a structured mesh 18
I usually call that surface interface. And be careful with this tech-nique,
size matters here, your TRI and Quad should be of the same size
(Tri 1.3 bigger than Quad) otherwise the mesh quality will be bad. Since
i love to see things in action, let us apply this to our cube inside cube,
here are some screen shots:
(a) A sector (b) A sector
(c) A sector (d) full meshing
Figure 15: Before and after.

24. 6 CONCLUS ION
That was it for this small documentation. This is the first version of this
book, yet more has to be added later, i will update this book with new
informations regularly. To be honest, i was too excited to put it on-line.
Of course, everybody who wishes to participate in the writing of this
book is more than welcome. Just send me and e-mail.
I need your support to continue with updating this book. I will feel very
happy if I can get some feedbacks and critics in this website:
http://goo.gl/9BkiO
Thank You
19