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Hybrid Mesh Problems with Gridgen

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Old   March 28, 2013, 14:26
Default Hybrid Mesh Problems with Gridgen
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Robin Prenter
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Hi everyone,

I am trying to create a 2D hybrid mesh with Gridgen (v. 15.18). The geometry consists of a turbine vane, that has an internal cooling cavity and a slot for film cooling. Essentially, I would like most of the mesh to be unstructured, with a structured boundary layer around the blade profile.

When I export the grid to Fluent, I get the error:
"cell(s) might not be closed, e.g. a face is missing fluent ...." and something about a cell centroid. I also get the "Left-handed" faces error.

I'm not sure that I'm doing the domains and blocks correctly. Any help, advice, anything would be appreciated!

Thanks,
Robin
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Old   March 29, 2013, 12:03
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Chris Sideroff
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Robin,

Sorry for the slow reply. My default answer for 2D meshes with Fluent is to be mindful of the domain orientation. First, the domains must be in the XY plane. Second, the domain normals must be pointing in the +z direction. For unstructured domains this is obvious. For structured domains, it's less obvious and you determine it from the IJ computational coordinates, ie. K should point in the +z direction. See this previous explanation I gave:

Pointwise to Fluent problem

Let me know if that is the issue, otherwise you'll need to provide some more information.

Regards, Chris

Quote:
Originally Posted by osuRobin View Post
Hi everyone,

I am trying to create a 2D hybrid mesh with Gridgen (v. 15.18). The geometry consists of a turbine vane, that has an internal cooling cavity and a slot for film cooling. Essentially, I would like most of the mesh to be unstructured, with a structured boundary layer around the blade profile.

When I export the grid to Fluent, I get the error:
"cell(s) might not be closed, e.g. a face is missing fluent ...." and something about a cell centroid. I also get the "Left-handed" faces error.

I'm not sure that I'm doing the domains and blocks correctly. Any help, advice, anything would be appreciated!

Thanks,
Robin
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Old   March 29, 2013, 12:59
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Robin Prenter
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Hi Chris,

Thanks for your reply. I took a look at your other post, and I don't think orientation is my problem. I think the problem has to do with the interface between the structured and unstructured domains, and perhaps also with how I am creating the domains/blocks.

What other information can I provide that would help?

Thanks so much!
Robin
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Old   March 29, 2013, 13:12
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Chris Sideroff
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Quote:
Originally Posted by osuRobin View Post
Hi Chris,

Thanks for your reply. I took a look at your other post, and I don't think orientation is my problem. I think the problem has to do with the interface between the structured and unstructured domains, and perhaps also with how I am creating the domains/blocks.

What other information can I provide that would help?

Thanks so much!
Robin
Well the best would be if you can send me the mesh file to inspect. If you can't send it, the next best thing would be to post pictures of where you think the problem is occurring. If you can send it to me send me a private message and I'll give you my email address.

Something else just came to my mind. You need to create one volume condition for each of your Fluent zones. For example, if you had 6 domains representing your fluid region, create a volume condition and assign those 6 domains to the fluid VC. Same for the solid region. It's important to assign your domains to volume conditions for Fluent export. Otherwise the Pointwise will create one VC and thus a Fluent zone for each domain it exports - generally not what you want.

-Chris
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Old   March 21, 2014, 12:39
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Quote:
Originally Posted by cnsidero View Post
Well the best would be if you can send me the mesh file to inspect. If you can't send it, the next best thing would be to post pictures of where you think the problem is occurring. If you can send it to me send me a private message and I'll give you my email address.

Something else just came to my mind. You need to create one volume condition for each of your Fluent zones. For example, if you had 6 domains representing your fluid region, create a volume condition and assign those 6 domains to the fluid VC. Same for the solid region. It's important to assign your domains to volume conditions for Fluent export. Otherwise the Pointwise will create one VC and thus a Fluent zone for each domain it exports - generally not what you want.

-Chris
Hi Chris,

I'm having the similar problem.
I try to separate my fluid region, and force one part of it to be laminar.
The missing internal faces problem occurs on this particular part of fluid and where it connect with the other parts of fluid.
Do you have any ideas for my problem?
Thanks in advance.

Yi
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Old   March 24, 2014, 14:05
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Quote:
Originally Posted by hy2049 View Post
Hi Chris,

I'm having the similar problem.
I try to separate my fluid region, and force one part of it to be laminar.
The missing internal faces problem occurs on this particular part of fluid and where it connect with the other parts of fluid.
Do you have any ideas for my problem?
Thanks in advance.

Yi
It would help if you could be more specific but I'll try to describe the general setup.

First, did you set up you're problem using VC's like a described earlier in this thread? See the attached image as an example of what I meant. I have one VC for the 4 structured domains around the ellipse and the other for the outer domain. As I also noted above, it's important to set the domain normals pointing in the +'ve z direction before exporting.

When you export the mesh and load this into Fluent, there will be two cell zones that correspond to the VC setup in Pointwise. Note that Fluent will automatically create an interior zone between the VCs - this is because Fluent needs a zone to pass information between cell zones. If you simply want the flow to pass from cell zone to cell zone, uninterrupted, you can safely leave and ignore this interior zone.

Let me know if this helps, Chris
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Old   March 24, 2014, 15:25
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Quote:
Originally Posted by cnsidero View Post
It would help if you could be more specific but I'll try to describe the general setup.

First, did you set up you're problem using VC's like a described earlier in this thread? See the attached image as an example of what I meant. I have one VC for the 4 structured domains around the ellipse and the other for the outer domain. As I also noted above, it's important to set the domain normals pointing in the +'ve z direction before exporting.

When you export the mesh and load this into Fluent, there will be two cell zones that correspond to the VC setup in Pointwise. Note that Fluent will automatically create an interior zone between the VCs - this is because Fluent needs a zone to pass information between cell zones. If you simply want the flow to pass from cell zone to cell zone, uninterrupted, you can safely leave and ignore this interior zone.

Let me know if this helps, Chris
It helps a lot. Thank you so much.
Hopefully I solved this problem. I'm testing the calculation now.
But every time I need to import my mesh into ICEM and then to fluent. It keeps telling me that there are critical error when I try to read the case from Pointwise in Fluent directly.
And everytime I need to use ICEM to check the problem and fix the problem before I load it in Fluent.

Yi
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Old   March 25, 2014, 09:07
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Quote:
Originally Posted by hy2049 View Post
It keeps telling me that there are critical error when I try to read the case from Pointwise in Fluent directly.
This leads me to believe the domain normals are not correctly orientented before exporting.

Refer to my first reply in this thread for the step-by-step: Hybrid Mesh Problems with Gridgen
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Old   March 27, 2014, 02:01
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Quote:
Originally Posted by cnsidero View Post
This leads me to believe the domain normals are not correctly orientented before exporting.

Refer to my first reply in this thread for the step-by-step: Hybrid Mesh Problems with Gridgen
I tried to follow it step by step. Other parts work well, only the cells where laminar parts connect with outside parts.
I will try it again later. Thank you very much for you replying.

Yi
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