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Questions about Y+ and Transitional Flows

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Old   March 4, 2008, 02:09
Default Questions about Y+ and Transitional Flows
  #1
Justin Figley
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Greetings, I am working on a case for which 2mm semi-circular channels contain helium flowing with a Reynolds number of about 3200. I am currently using a k-omega model with the transitional flow option enabled. When I look at my Y+ values I cannot get them within the limits required for turbulent flows.

Are the typical limits on Y+ the same for transitional flows as they are for turbulent flows? How important is Y+ Resolution for transitional cases?

The small size of the channel is giving me issues meshing in gambit without getting inverted elements as I try to refine it and add channels to the model. If anyone has any advice for meshing small channels while maintaining any sort of real grid resolution they would be greatly appreciated.

Thanks, Justin
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Old   March 4, 2008, 07:42
Default Re: Questions about Y+ and Transitional Flows
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Robert
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Did You try the adaption? It doesn't need to recreate the mesh with Gambit, the FLUENT refine the mesh where it is needed.

You find it in the menu: "Adapt"/"Yplus/Ystar"

Bye

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Old   March 4, 2008, 14:24
Default Re: Questions about Y+ and Transitional Flows
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justin figley
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I have tried y+ adaptation. I have tried it several times, it seems to help very little.

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Old   March 4, 2008, 14:50
Default Re: Questions about Y+ and Transitional Flows
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Robert
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I don't know, how many cells has the mesh. So, if the wall y+ larger than the limit, you have to adapt the mesh. The method is the following: -Calculate the flow field -check the y+ -if larger than the limit->adapt -Continue the iteration until convergence -check again the y+, if larger, adapt again, continue iteration until convergence -and repeat until the y+ in a good range.

If the size of cells are very big near the wall, you have to adapt many times the wall.
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Old   March 5, 2008, 17:25
Default Re: Questions about Y+ and Transitional Flows
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Justin Figley
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Thanks for the suggestion of doing the adaptation as an iterative process. I will give this a try.
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