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Old   March 30, 2010, 00:59
Default Validation
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Mohsin Mukhtar
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hello

I have made a model. It is a cylinder with 1 inlet at the top and 4 inlets on its lower side. From top coal wil enter and from sides air will enter to provide mixing at the outlets. for this model i used tetrahedral meshes and hexahedral meshes.

For valdiation of the model i wanted to have results without the 4 inlets for air which provide mixing so that i can compare and check the results. Could anyone please tell me whateher i have to use the same mesh size and mesh types for validation or i can change the mesh type (to hexahedral ) for the later case (without 4 inlets) and calculate the results at the outlet?because without 4 inlets i can make hexahedral meshes all over teh model easily.

In short please answer to this : For validation/comparison of the model is it necessary to have same mesh type, mesh size for the same geometry?
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Old   March 30, 2010, 12:11
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Chris
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CFD calculations are mesh dependent, so it would be a good idea to be as close as possible. I would be especially careful switching between hex and tet. Think about it like this: if you were doing a physical experiment, you would try to minimize extraneous variables. CFD isn't any different. At the very least, you'll need to spend extra effort just to convince everyone that it was ok to do the things you mentioned.

There are techniques out there for validating solutions, such as Roache's Grid Convergence Index:

http://www.grc.nasa.gov/WWW/wind/val.../spatconv.html

Something like this would probably be the best way to validate your solutions.
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Old   March 31, 2010, 04:30
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Mohsin Mukhtar
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Thank you very much. I think I need to study this in detail and do some tutorials in order to understand about convergence validation.

Thank you again
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