CFD Online Discussion Forums

CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)
-   ANSYS Meshing & Geometry (https://www.cfd-online.com/Forums/ansys-meshing/)
-   -   [ICEM] O-grid Blocking (https://www.cfd-online.com/Forums/ansys-meshing/188380-o-grid-blocking.html)

beyonder1 May 29, 2017 01:46

O-grid Blocking
 
1 Attachment(s)
Hi,
I have trouble understanding the difference between these two type of blocking.
Consider a case of a concentric cylinder.

After Initializing block, I create O-grid,
1. Using only Block.
2. Using block and two faces.

Why there is extra block created in case of (1) at inlet/outlet. Also, the meshing is different at inlet/outlet compared to just inside. What is the purpose of this type of meshing?

venturi May 29, 2017 07:42

There is something wrong with your mesh, in both cases. I always use the second method, select the block and the inlet and outlet faces. What you should get is closer to the image attached.

Maybe is an association problem.

I am pretty sure the ICEM tutorial has an example for this.

http://imgur.com/a/3DXNa
http://imgur.com/a/3DXNa

venturi May 29, 2017 07:44

http://i.imgur.com/I2Z85zs.png

beyonder1 May 29, 2017 09:28

Yes, I am also getting the same thing you have uploaded when I use the second method. But the question I have is:
- What is wrong with the First Method if there is something?
- If you haven't tried First method earlier, can you check if you are getting something different on faces.
- What is the purpose of selecting inlet/oulet faces in second method? I know I am getting results with it but theoretically speaking why should we do this?

venturi May 29, 2017 09:42

You have to select the faces so that ICEM knows in which direction it should perform the o'grid.

For instance, try selecting two opposing wall faces, you'll see that the constructed o'grid will be different.

This is useful when you have a more complex geometry. Another example is when you have two connecting pipes, sometimes you can even define only one face for the o'grid. This way the o'grid will stop when it find another block.

johny0688 May 30, 2017 02:37

When you use only block without pointing faces the o-grid is created around hole block as a "shell" form, so the mesh from case 1 is good. When pointing face you told on which faces the o-grid will be projecting. Try to create ogrid by block and only one face e.g. inlet. Cut your geometry by plane along pipe and you will see how it works.

beyonder1 May 30, 2017 03:11

Quote:

Originally Posted by johny0688 (Post 650852)
When you use only block without pointing faces the o-grid is created around hole block as a "shell" form, so the mesh from case 1 is good.

I still don't understand why case 1(using only block as 'shell') is good. It doesn't create o-grid on face and mesh will be skewed there. I want to know in which type of geometry one should prefer 'block only case' over 'block with face case.'

johny0688 May 30, 2017 03:35

Quote:

Originally Posted by shubham2941 (Post 650857)
I still don't understand why case 1(using only block as 'shell') is good. It doesn't create o-grid on face and mesh will be skewed there.

Ok, we have misunderstanding ;) When I said 'is good' I mean that when you do not point faces, only block, the mesh should look exactly like in your picture. I mean it is not ICEM error. Of course the mesh from case 1 is not good.


Quote:

I want to know in which type of geometry one should prefer 'block only case' over 'block with face case.
It is rather due to the flow, not geometry. The o-grid is usually attached to the wall to calculate boundary layer. You should analyse your case and decided where o-grid should be attached and where not.


All times are GMT -4. The time now is 17:44.