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Old   October 27, 2016, 09:20
Default replace cfx scalable wall function
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Grecu Ionut Stelian
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Hi,

I want to replace the scalable wall function used in the k-epsilon turbulence model, with my own wall function that I could use it for k-epsilon turbulence model.

Until now i tried with user defined wall function (ch 4.2.4. User Defined Wall Functions) but it isn't working.

How can I do it?

Thank you
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Old   October 27, 2016, 17:15
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Glenn Horrocks
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What isn't working about it? That feature should do what you are looking for.
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Old   October 31, 2016, 10:24
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Quote:
Originally Posted by ghorrocks View Post
What isn't working about it? That feature should do what you are looking for.
Hi Glenn, thank you for the reply.

I am doing a test in a diffuser, and for the Wall Function Transfer Coefficient I entered a value of 5 [m/s], then I run the simulation.
When I represent the velocity in the diffuser I have values from 0.2 to 1.4 m/s, shouldn't I have 5 m/s over the whole velocity?
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File Type: txt test.txt (4.5 KB, 12 views)
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Old   October 31, 2016, 13:56
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Not sure what is your understanding of the wall function concept. For the momentum equation, the wall function transfer coefficient relates the wall shear with the velocity at the wall and the control volume, i.e.

Wall Shear = WallFunction Transfer Coefficient * (Vertex Velocity - Wall Velocity)

The analogy to heat transfer

Heat Flux = Heat Transfer Wall Function Transfer Coefficient * (Vertex Temperature - Wall Temperature)

Hope the above helps,
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Old   November 1, 2016, 01:42
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Quote:
Originally Posted by Opaque View Post
Not sure what is your understanding of the wall function concept. For the momentum equation, the wall function transfer coefficient relates the wall shear with the velocity at the wall and the control volume, i.e.

Wall Shear = WallFunction Transfer Coefficient * (Vertex Velocity - Wall Velocity)

The analogy to heat transfer

Heat Flux = Heat Transfer Wall Function Transfer Coefficient * (Vertex Temperature - Wall Temperature)

Hope the above helps,
Hi Opaque, thank you for the reply.
Can you please give me some documents to learn more about it, or some web addresses?
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Old   November 1, 2016, 16:50
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Any CFD textbook will have a chapter on turbulence modelling which covers this. Or you can probably find some descriptions of this stuff with a google search too - it should not be too hard to find.
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