postprocessing - TauW in custom field functions

August 20, 2008, 15:26

Dear All,

I'd like to output a plot of U+ (velocity normalised by friction velocity) against Y+ along a line extending vertically from a surface. I hoped to write a custom field function (cff) for this.

Firstly I wrote a cff for friction velocity;

Utau = SQRT(TauW/Roe)

Next a cff for U+

U+ = Ulocal/Utau

Of course when I plot U+ along a line, as soon as the line leaves the wall surface I get zero U+, because Wall shear TauW only has value adjacent to the wall.

Can anyone suggest a means of extracting the Wall shear value at a point for use as a constant in a cff?

I think the same result can be achieved by outputting TauW into a file and calculating U+ outside of fluent, but the aim should be to automate as much as posible and I hoped there was a facility within Fluent to enable this.

Thanks in anticipation.

Ianto

renli05 · September 29, 2011, 11:59

hi,Ianto ,I'm now encountering the same problem as you. Have you worked out this problem? I want to define a corrected uplus in fluent with the Van Direst transformation.
uc=Int(rou/rouw)dU+
here Int means integration.
I think it is hard to define such a quantity in custom field function.Maybe I should use UDF. But I am not familar with this. Can you give some sugguestions. Thank you in advance.

August 20, 2008, 15:26	postprocessing - TauW in custom field functions	#1
Ianto Guest Posts: n/a	Dear All, I'd like to output a plot of U+ (velocity normalised by friction velocity) against Y+ along a line extending vertically from a surface. I hoped to write a custom field function (cff) for this. Firstly I wrote a cff for friction velocity; Utau = SQRT(TauW/Roe) Next a cff for U+ U+ = Ulocal/Utau Of course when I plot U+ along a line, as soon as the line leaves the wall surface I get zero U+, because Wall shear TauW only has value adjacent to the wall. Can anyone suggest a means of extracting the Wall shear value at a point for use as a constant in a cff? I think the same result can be achieved by outputting TauW into a file and calculating U+ outside of fluent, but the aim should be to automate as much as posible and I hoped there was a facility within Fluent to enable this. Thanks in anticipation. Ianto

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September 29, 2011, 11:59		#2
renli05 New Member Join Date: Jul 2011 Posts: 2 Rep Power: 0	hi,Ianto ,I'm now encountering the same problem as you. Have you worked out this problem? I want to define a corrected uplus in fluent with the Van Direst transformation. uc=Int(rou/rouw)dU+ here Int means integration. I think it is hard to define such a quantity in custom field function.Maybe I should use UDF. But I am not familar with this. Can you give some sugguestions. Thank you in advance.