[AS_Aero]

Hi

I am doing a rotor , stator simulation using CFX.
The simulation is running without any error, but I have some doubt regarding the values the simulation is giving me while its running, which somewhere I read that these values are not good, that means my mesh has to be remeshed. But what exactly should I change in my mesh to have a good value and where can I see these values before running the simulation ? Mesh statistics doesnt show these Ortho Angle or Exp Factor. So am not sure how to change this. But running like this will cause any serious trouble in results or not ?

+--------------------------------------------------------------------+
| Mesh Statistics |
+--------------------------------------------------------------------+
| Domain Name | Orthog. Angle | Exp. Factor | Aspect Ratio |
+----------------------+---------------+--------------+--------------+
| | Minimum [deg] | Maximum | Maximum |
+----------------------+---------------+--------------+--------------+
| Rotor | 18.3 ! | 15 ok | 61 OK |
| Stator | 1.6 ! | 46326 ! | 4692 OK |
| Global | 1.6 ! | 46326 ! | 4692 OK |
+----------------------+---------------+--------------+--------------+
| | %! %ok %OK | %! %ok %OK | %! %ok %OK |
+----------------------+---------------+--------------+--------------+
| Rotor | <1 18 82 | 0 1 99 | 0 0 100 |
| Stator | <1 2 98 | <1 2 98 | 0 0 100 |
| Global | <1 16 84 | <1 1 99 | 0 0 100 |
+----------------------+---------------+--------------+--------------+

Domain Name : Rotor

Total Number of Nodes = 19833852

Total Number of Elements = 19084500
Total Number of Prisms = 78000
Total Number of Hexahedrons = 19006500

Total Number of Faces = 2762460

Domain Name : Stator

Total Number of Nodes = 2368689

Total Number of Elements = 12756684
Total Number of Tetrahedrons = 12171425
Total Number of Prisms = 580565
Total Number of Pyramids = 4694

Total Number of Faces = 383063

Global Statistics :

Global Number of Nodes = 22202541

Global Number of Elements = 31841184
Total Number of Tetrahedrons = 12171425
Total Number of Prisms = 658565
Total Number of Hexahedrons = 19006500
Total Number of Pyramids = 4694


-----------------------------------------------------------------------
And what is the correct range of values I could have in that case ?
Thanks in advance !!

[ghorrocks]

You can visualise the mesh quality metrics in CFD-Post or in ICEM.

What do you change to improve mesh quality? That is a bit like asking a builder how to build a house. You need to look at what is causing poor quality and fix it. To do that effectively you need to have some experience in meshing and the tools available, and you can only get that by doing the tutorials, doing some training, and trying all the options and see what they do.

[AS_Aero]

Hi Glenn

Yeah sure, doing mesh tutorials will help, but my doubt is for these orthogonal angle or expansion factor, in ansys meshing I cant see these values in the mesh statistics. So I have to load the mesh in CFD-Post and then see the values. But when I am doing the entire project in the workbench setup, how can I load the mesh in CFD Post, it doesnt allow me to do that way. And most of the time when am using unstructured mesh I get low orthogonal quality and high skewness. I have been trying to find some ways to reduce it, but not successfull. And most of the time the Inflation layer with first layer thickness,also creating bad quality cells.
Anyways kindly let me know how I can check those orthogonal angle and expansion factor before running the case ? I am using CFX on the workbench framework, so I cannot directly open the Results to check the mesh quality. I have to run the case.
So if there is any ways kindly let me know.

[Gert-Jan]

You can always open CFD-Post standalone and read in the .msh-file from the workbench mesher. But I don't know the connection to the qualities in the mesher (WB-mesher, ICEM), the solvers (Fluent and CFX) and Post. All have their own definitions.

To be honest, only if results become very bad, or divergence occurs, I npay attention to the mesh messages in the output file. I always use ICEM with full control of the mesh quality by smoothing, over, and over, and over, and over..........

[AS_Aero]

ICEM Meshing is good, but it takes lot of time to understand how to use it for complex geometries. Can you tell me how can we check in CFD-Post for the bad quality cells in the entire domain ?

[AS_Aero]

Hi Glenn

Can you tell me how I can check the bad quality cells with huge expansion factor in CFD Post for the entire domain ? What is the option and where is it ?

[ghorrocks]

Load the file in CFD-Post. Then go to the "Calculators" tab and select Mesh Calculator. Select the mesh statistic you want to calculate and press calculate. It will now be added to your variable list and you can use it to colour surfaces, draw isosurfaces and all the other CFD-Post functions.

[AS_Aero]

Hi Glenn

Since we were discussing about the meshing
I jsut want to ask you regarding the issue I am facing with the first layer inflation and my poor quality cell is exactly on the inflation layer, so am not sure how I can get rid of this.

[ghorrocks]

I am not sure how to fix it either as I do not know where the poor element is, what it looks like and what constraints you have to work with.

Meshing is a skill which takes time and practice. Generating a good quality mesh will make a big difference so is worth investing in. So all I can recommend is to try lots of things, like smoothing, different meshing techniques and even manually adjusting problem areas and see how you go.

[AS_Aero]

Thanks a lot for your advise.