How to modify the Schmidt number in CFX for additional variables model?

rockzh · February 8, 2012, 19:58

In order to simulate the thermal tracing,I apply additional variables (as temperture T)in the caculation.Then,how to change the turbulence Schmidt number in CFX?

ghorrocks · February 8, 2012, 22:32

You can just enter whatever Schmidt number you like. But I seem to remember it must be constant in space and time.

rockzh · February 8, 2012, 23:00

where can i do this in CFX ?

ghorrocks · February 9, 2012, 06:23

In the turbulence model details, I cannot remember the details of exactly where as I am not at the computer right now.

Lance · February 9, 2012, 10:05

Quote:

Originally Posted by rockzh

where can i do this in CFX ?

For a turbulence model, you'll find the Turbulent Schmidt number under Fluid models/Turbulence/Advanced Turbulence Control/K Coefficients/Turbulent Flux Closure/Turbulent Schmidt Number (for k-epsilon model, slightly different for SST or any other model)

For an additional variable it's under Fluid Models/Additional Variable Models/Turbulent Flux Closure/Turb. Schmidt Num.

rockzh · February 9, 2012, 20:39

Quote:

Originally Posted by Lance

For a turbulence model, you'll find the Turbulent Schmidt number under Fluid models/Turbulence/Advanced Turbulence Control/K Coefficients/Turbulent Flux Closure/Turbulent Schmidt Number (for k-epsilon model, slightly different for SST or any other model)

For an additional variable it's under Fluid Models/Additional Variable Models/Turbulent Flux Closure/Turb. Schmidt Num.

Thank you for replay.
"For an additional variable it's under Fluid Models/Additional Variable Models/Turbulent Flux Closure/Turb. Schmidt Num" is found in CFX GUI?
The version i used is 12.1.
In "Fluid Models/Additional Variable Models" option,there is no "Turbulent Flux Closure" option.

ghorrocks · February 9, 2012, 21:08

Is your additional variable a convection and diffusion AV? This is the only type of AV where you get these options I suspect.

rockzh · February 10, 2012, 00:07

I am not clear about that.
how can i define the AV as convection adn diffusion?
I add a AV in "Expression,Functions and Variables-Additional Variables",and define the AV option as Transport Equation. Is it right?

ghorrocks · February 10, 2012, 00:13

Transport equation is convection only. Turbulence adds diffusion so is not available for that AV option. You want a transport & diffusion AV.

Lance · February 10, 2012, 02:58

Quote:

Originally Posted by ghorrocks

Transport equation is convection only. Turbulence adds diffusion so is not available for that AV option. You want a transport & diffusion AV.

??
The transport equation for AVs include both convection and diffusion, so there should be an option for Turbulent Flux Closure. The settings available in the gui are the Eddy Diffusivity model and the Turbulent Schmidt number.

ghorrocks · February 10, 2012, 05:27

Firstly I must admit I did not check this answer before I posted it so if I goofed then thanks Lance for picking it up.

I seem to remember that AVs could be either algebraic equation, transport equation only, diffusion equation only or transport and diffusion equation. The transport equation equation option has no diffusion component. But if my memory is incorrect then oops

rockzh · February 10, 2012, 20:36

Thank you for all your replay.
I find the reason for the Schmidt seeting problem.
Befor version 12.1 of CFX ,threre is no Turbulent Flux Closure option in GUI.
We have to use CCL for changing the Schmidt Nb.I find the related CCL as follows:
HEAT TRANSFER MODEL:
Option = Thermal Energy
TURBULENT FLUX CLOSURE:
Option = Eddy Diffusivity
Turbulent Prandtl Number = XX
END
END

After i import the CCL,how to see the changed Schmidt value?

February 8, 2012, 19:58	How to modify the Schmidt number in CFX for additional variables model?	#1
rockzh New Member Darren Zhang Join Date: Nov 2011 Location: China Posts: 20 Rep Power: 14	In order to simulate the thermal tracing,I apply additional variables (as temperture T)in the caculation.Then,how to change the turbulence Schmidt number in CFX?

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February 8, 2012, 22:32		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	You can just enter whatever Schmidt number you like. But I seem to remember it must be constant in space and time.

February 8, 2012, 23:00		#3
rockzh New Member Darren Zhang Join Date: Nov 2011 Location: China Posts: 20 Rep Power: 14	where can i do this in CFX ?

February 9, 2012, 06:23		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	In the turbulence model details, I cannot remember the details of exactly where as I am not at the computer right now.

February 9, 2012, 21:08		#7
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Is your additional variable a convection and diffusion AV? This is the only type of AV where you get these options I suspect.

February 10, 2012, 00:07		#8
rockzh New Member Darren Zhang Join Date: Nov 2011 Location: China Posts: 20 Rep Power: 14	I am not clear about that. how can i define the AV as convection adn diffusion? I add a AV in "Expression,Functions and Variables-Additional Variables",and define the AV option as Transport Equation. Is it right?

February 10, 2012, 00:13		#9
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Transport equation is convection only. Turbulence adds diffusion so is not available for that AV option. You want a transport & diffusion AV.

February 10, 2012, 05:27		#11
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Firstly I must admit I did not check this answer before I posted it so if I goofed then thanks Lance for picking it up. I seem to remember that AVs could be either algebraic equation, transport equation only, diffusion equation only or transport and diffusion equation. The transport equation equation option has no diffusion component. But if my memory is incorrect then oops

February 10, 2012, 20:36		#12
rockzh New Member Darren Zhang Join Date: Nov 2011 Location: China Posts: 20 Rep Power: 14	Thank you for all your replay. I find the reason for the Schmidt seeting problem. Befor version 12.1 of CFX ,threre is no Turbulent Flux Closure option in GUI. We have to use CCL for changing the Schmidt Nb.I find the related CCL as follows: HEAT TRANSFER MODEL: Option = Thermal Energy TURBULENT FLUX CLOSURE: Option = Eddy Diffusivity Turbulent Prandtl Number = XX END END After i import the CCL,how to see the changed Schmidt value?