## 3D Design

Topics related to Ansys Discovery and Ansys SpaceClaim.

#### Creation of Periodic B.C in ICEM

• Aras karimi
Subscriber

Hi to all,

I want to create a periodic mesh on the domain below, and the front page of the domain (purple color) will be named Periodic 1 and the back page of the domain (blue color) will be named Periodic 2:

I need to establish a Translational Periodic boundary condition. I created a mesh structure. Now please help how can I apply this boundary condition?

The front surface of the domain is located at the origin of the coordinates, and the back surface of the domain is located in the -Z direction and at a distance of -0.2 meters from the origin of the coordinates. (In other words, the span length of the airfoil is 0.2 meters)

Earlier, I read that I should first come to this section and select the type of boundary condition. There is also a parameter called offset. What number should be written?

And what should I do next?

Thank you for helping me

Regards

Ansys Employee

Offset in Translation periodic should be distance between two periodic surfaces.

Please go through help manual for more details

Regards,

Keyur

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• Aras karimi
Subscriber

The distance between the two surfaces is 0.2 meters, the front surface is located at the origin of the coordinates and the back surface is located at -0.2 meters from the origin of the coordinates, in other words, the back surface is located in  -Z.

Now, there are three zeros in the offset section. Does that mean three values should be written here?

What numbers should I write?

Thank you

Ansys Employee
• Aras karimi
Subscriber

well i know

What number should I write now?

Should I put    0  0  -0.2      or      0  0  0.2  ?

Don't I need to write values for x and y?

• Aras karimi
Subscriber

Dear Keyur,

The front surface of the domain is located at the origin of the coordinates, and the back surface of the domain is located in the -Z direction and at a distance of -0.2 meters from the origin of the coordinates. (In other words, the span length of the airfoil is 0.2 meters)

I went to ICEM Help and found the following:

I'm still confused and I don't know what number should I put for the offset ?

If you help me, I will thank you a thousand times.

Regards

Ansys Employee
• Aras karimi
Subscriber

Should I put    0  0  -0.2      or      0  0  0.2   for offset?

• Aras karimi
Subscriber

Dear Keyur,

Should I put    0  0  -0.2      or      0  0  0.2   for offset?

• mjmiddle
Ansys Employee

The negative or positive value does not matter. You can use either 0  0  -0.2      or      0  0  0.2.

It just defines a distance when node locations will be linked to be the same values in the directions normal to this vector and matching in vector length distance along the vector. After setting up the periodicity direction in the global settings, you must still link the block vertices. This is shown in the ICEM CFD training. Two lectures slides are shown below. The example shows angular periodicity, but the procedure is the same for linear periodicity:

You will need to design your blocking scheme so that the face structure matches at the periodic faces.

• Aras karimi
Subscriber

Thank you

According to the type of blocking I posted earlier, will the following happen?

(You will need to design your blocking scheme so that the face structure matches at the periodic faces.

And is my blocking correct for this?

• Aras karimi
Subscriber

Dear mjmiddle,

For another case, I need to create a symmetry boundary condition between the front and back surfaces of the domain.That is, the front surface of  Symmetry1  and the back surface of Domain Symmetry2.

For this situation, do I not need to set the Global Mesh Setup? And only and only in the Part Boundary Conditions section, should I define two surfaces symmetrically?

I mean, in order to create a symmetric boundary condition, there is no need for special work like creating a periodic boundary condition?

Regards

• mjmiddle
Ansys Employee

If you understand the direction you want to make periodic, you should be able to answer this question yourself. So to test you, what do you think? Do you forsee problems with setting up the periodicity? Start linking the vertices as desribed in the two training pages and you'll find out.

• Aras karimi
Subscriber

I have applied the periodic boundary condition before, I just wanted to make sure I went through the steps correctly and entered the offset coordinates correctly. This is the following figure that worked correctly:

But I still don’t understand the difference between   0 0 -0.2   and   0 0 0.2 !!!

• Aras karimi
Subscriber

Dear mjmiddle,

For another case, I need to create a symmetry boundary condition between the front and back surfaces of the domain.That is, the front surface of  Symmetry1  and the back surface of Domain Symmetry2.

For this situation, do I not need to set the Global Mesh Setup? And only and only in the Part Boundary Conditions section, should I define two surfaces symmetrically?

I mean, in order to create a symmetric boundary condition, there is no need for special work like creating a periodic boundary condition?

Regards

• mjmiddle
Ansys Employee

The boundary conditions for solver ouptuts are a convenience for setup to the solver. You don't need to set any of those in ICEM CFD. You can set them up entirely in the solver. ICEM CFD only has a very limited selection of BC conditions for output to the solvers anyway. And they are different for each solver and specific to each solver.

A symmetry BC means typically a mirror symmetry, as though you mirrored the model across a plane into empty space. There is no linking to set up. There is no symmetry1 and symmetry2 that are linked in this case. You are getting the solver term "symmetry" mixed up with the "periodicity" term in ICEM CFD.

As far as specifying 0 0 -0.2   or   0 0 0.2 for the linear periodicity, they are both vectors along the same line in space. Only the direction is flipped. But direction is not important. The mesh is equal on both periodic sides when you link the vertices of the blocking. They are coupled. It chooses one side as the master, which you don't always know ahead of time until you try to change edge params on one side and you find out which side has the effect.

• Aras karimi
Subscriber

I only have two other small problems with the meshing. Should I ask in the same topic  ([ICEM] Airfoil Meshing in icem-cfd) ?

• Aras karimi
Subscriber

Dear  mjmiddle ,

In the new thread below I have raised a problem when studying the independence of the solution from the mesh:

(https://forum.ansys.com/forums/topic/mesh-independence-study-4/#post-314495)

I will be grateful if you help me

Thank you a thousand times

• Aras karimi
Subscriber

Hi Dear mjmiddle,

I want to create mesh and periodic boundary condition for another mode.

This time, the front page of the flow is at   Z= -0.7mm   and the back page of the flow is at   Z= -40.7mm. That is, the length of the airfoil span is 40mm.

What number should I put for the offset?

• Aras karimi
Subscriber

Hi Dear mjmiddle,

I want to create mesh and periodic boundary condition for another mode.

This time, the front page of the flow is at  Z= -0.7mm  and the back page of the flow is at   Z= -40.7mm. That is, the length of the airfoil span is 40mm.

What number should I put for the offset?

• Govindan Nagappan
Ansys Employee

Aras, You can use the same logic that you used for the first model. If the periodic faces are offset by a distance of 40mm in Z direction, you can enter offset of 0 0 40