Effective thermal conductivity in turbulent flow

Chander · August 17, 2011, 12:41

I am simulating single phase incompressible turbulent flow using basic k-omega model in CFX 12. I want to know the effective thermal conductivity from the results at each point in fluid domain. Now
effective thermal conductivity = thermal conductivity of fluid + Cp * eddy viscosity/ turbulent Pr

eddy viscosity is listed as a variable in CFX post can be accessed. Where is the value of turbulent Pr listed? If I am thinking correctly, this is an empirical constant for the k-omega model but I could not find its value in the documentation.

Thanks for your help.

Best,
Chander

ghorrocks · August 17, 2011, 19:41

It is set in the turbulence model details in CFX-Pre. I think by default it is 0.7 but you should check this.

Chander · August 17, 2011, 20:24

Quote:

Originally Posted by ghorrocks

It is set in the turbulence model details in CFX-Pre. I think by default it is 0.7 but you should check this.

I checked in CFX pre but I do not see any entry for turbulent Pr there.
Anywhere else I could look?

Also, is the way I am trying to account for turbulence in thermal conductivity ( the formula in my above post) correct?

ghorrocks · August 17, 2011, 20:30

In CFX-Pre, setting the domain: Fluid Models/Turbulence/Turbulence Flux Closure for Heat transfer/Turbulent Prandtl Number. Looks like the default for k-omega is 0.9.

Chander · August 18, 2011, 10:55

Quote:

Originally Posted by ghorrocks

In CFX-Pre, setting the domain: Fluid Models/Turbulence/Turbulence Flux Closure for Heat transfer/Turbulent Prandtl Number. Looks like the default for k-omega is 0.9.

I could not see the option of '..Turbulence Flux Closure for Heat transfer/Turbulent Prandtl Number' in the domain settings. I am using version 12.1. Are you using a different version?

Also, the Ansys CFX support says that turbulent prandtl number is defined as sigma-omega and is equal to 2 as given in the cfx solver theory guide under k-omega model. But I dont see it among the options in CFX-Pre.

Does it mean it is hardcoded and not accesible in my version of 12.1?

ghorrocks · August 18, 2011, 19:45

I am on V13. Also you might need an advanced turbulence model license (or a full capability solver license) to access it.

August 17, 2011, 12:41	Effective thermal conductivity in turbulent flow	#1
Chander Senior Member Join Date: Oct 2010 Location: Zurich Posts: 176 Rep Power: 16	I am simulating single phase incompressible turbulent flow using basic k-omega model in CFX 12. I want to know the effective thermal conductivity from the results at each point in fluid domain. Now effective thermal conductivity = thermal conductivity of fluid + Cp * eddy viscosity/ turbulent Pr eddy viscosity is listed as a variable in CFX post can be accessed. Where is the value of turbulent Pr listed? If I am thinking correctly, this is an empirical constant for the k-omega model but I could not find its value in the documentation. Thanks for your help. Best, Chander

August 17, 2011, 20:30		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	In CFX-Pre, setting the domain: Fluid Models/Turbulence/Turbulence Flux Closure for Heat transfer/Turbulent Prandtl Number. Looks like the default for k-omega is 0.9. rockzh likes this.

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August 17, 2011, 19:41		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	It is set in the turbulence model details in CFX-Pre. I think by default it is 0.7 but you should check this.

August 18, 2011, 19:45		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	I am on V13. Also you might need an advanced turbulence model license (or a full capability solver license) to access it.