replace cfx scalable wall function

Ionut G · October 27, 2016, 10:20

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

ghorrocks · October 27, 2016, 18:15

What isn't working about it? That feature should do what you are looking for.

Ionut G · October 31, 2016, 11:24

Quote:

Originally Posted by ghorrocks

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?

Opaque · October 31, 2016, 14:56

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,

Ionut G · November 1, 2016, 02:42

Quote:

Originally Posted by Opaque

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?

ghorrocks · November 1, 2016, 17:50

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.

October 27, 2016, 10:20	replace cfx scalable wall function	#1
Ionut G New Member G Ionut Join Date: Sep 2016 Posts: 29 Rep Power: 10	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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October 27, 2016, 18:15		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	What isn't working about it? That feature should do what you are looking for.

October 31, 2016, 14:56		#4
Opaque Senior Member Join Date: Jun 2009 Posts: 1,880 Rep Power: 33	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,

November 1, 2016, 17:50		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	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.