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Modelling Turbulent Wall Functions

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Old   August 25, 2010, 09:44
Default Modelling Turbulent Wall Functions
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Victor Azevedo
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Hi everybody,

I'm doing a multiphase flow simulation and I have to model the wall roughness by using "turbulent wall functions". The CFX Theory Guide have an expression for this, but the big problem is in one of the variables.

The turbulent wall function uses the variable u* (I think that's the friction velocity or shear velocity). This variable is available for me in the Solver, but when I run the case, in the Post this variable does not appear (CFX says that it not exist). I'm needing this variable to calculate the film thickness and other variables of my case.

So, I would like to ask you how can I put this variable in my expressions. Is there any syntax? Remember that's a multiphase flow case.

I attached my CCL file, so you can look. The u* is in the "Uaster" expression, and that's the origin of all my problem here. The "wall turbulent function" is in the "WTFC" expression.

Thanks for your help.
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Old   August 25, 2010, 18:03
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Glenn Horrocks
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Your function looks OK for a single phase flow. I suspect you need to get ustar for the phase you are interested in, not sure how to do that off the top of my head.

Does the ustar function work for a single phase flow?
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Old   August 26, 2010, 16:49
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Victor Azevedo
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Thanks for your answer ghorrocks.

I tried to run the case as single phase. Same problem on the ustar function. I'll try to run in other computer, and see if the same problem occur.

thanks again.
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Old   January 13, 2015, 10:38
Default implemanted new wall function
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adelo
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Hi everybody,

I'm doing a multiphase flow simulation and I want to implemanted a new wall function in CFX(



So, I would like to ask who can I add this new function(U*, C,K )


Thanks for your help.
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Old   January 13, 2015, 11:06
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You can read the following section in the documentation:

CFX-Solver Modeling Guide -> Turbulence and Near-Wall Modeling -> Modeling Flow Near the Wall -> User Defined Wall Functions
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Old   January 13, 2015, 15:02
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thank you very much I'm going to read this document
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Old   January 13, 2015, 15:22
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I want to write new formulas for this parameter (see document). in the indicated section I understood it shows me how to change a constant
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Old   January 13, 2015, 15:49
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The software does not let the user modify the ingredients of the built-in wall function. User modifications may not be compatible to what the developers implemented; therefore, the burden is on the user to implement it all.

Use the example provided in the documentation, and see where you can introduce the modifications you need.
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Old   January 13, 2015, 15:58
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you speak of this exemple in (ANSYS CFX-Solver Modeling Guide

4.2.4.3. Example of User-Defined Wall Function for Heat Flux)
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Old   January 14, 2015, 12:32
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Yes.. You can use that example as a template to create your custom wall function
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Old   January 14, 2015, 14:53
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thank you very much
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Old   January 14, 2015, 16:48
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before i do the ilmplemtation of my new wall function i need just to know how can I activate the wall function in simple case two phase flow
thanks for you help
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