Temperature gradient in CFX

Chander · July 9, 2011, 23:34

Hi,

I need to calculate local gradients of temperature in x,y,z direction. I am using CFX version 12.1.
However, it seems that CFX does not provide Temperature. gradient X etc values like it provides for other variables likes velocities and enthalpy.
I have tried using the option `Selected Variables` in Output control along with `All` selected for Output variable operators and ensuring Temperature to be in the `Output Variable list`. This according to the documentation should give be gradient values for temperature. But still CFX post does not show any such variable in the result file.

Is there anything else which I should try?

Otherwise CFX Post shows gradient values for static enthalpy as variables (Static ethalpy. Gradient X and so on). The fluid in my simulations is liquid water. I think I can get approximate values of temperature gradients by dividing the enthalpy gradient values by local value of cp of water ( I am using temperature dependent properties). This will amount to assuming that the water static enthalpy is only a function of temperature which I think is an ok assumption for liquid water. Do you think that this approach is correct?

Chander · July 11, 2011, 05:18

Anyone please ?

ghorrocks · July 11, 2011, 07:31

Maybe you should upgrade to V13. I think it has full support for variable spatial derivatives.

But I thought V12 had derviatives on temperature anyway. Are you sure it is not built in?

noslip · July 11, 2011, 08:16

temperature gradients are not automatically generated in cfx.

you can generate gradients of any (meaningful) scalar variables in post. create a new variable in the "variables" tab, set method from "expression" to "gradient" and select the variable you like (in your case the temperature).

this works in 12.1 btw.

hope this helps

Chander · July 11, 2011, 09:21

Thanks a lot Glenn and noslip.

This is very helpful. I wonder why it is not mentioned in the documentation for CFX-Post.

You have been a great help!!

ronggehejiumeizuiguo · January 7, 2015, 04:00

Quote:

Originally Posted by Chander

Thanks a lot Glenn and noslip.

This is very helpful. I wonder why it is not mentioned in the documentation for CFX-Post.

You have been a great help!!

hi，Chander
the temperature gradients I solved by dividing the static enthalpy gradient by Cp of water,at last,if u used this method?
Thanks.

July 9, 2011, 23:34	Temperature gradient in CFX	#1
Chander Senior Member Join Date: Oct 2010 Location: Zurich Posts: 176 Rep Power: 16	Hi, I need to calculate local gradients of temperature in x,y,z direction. I am using CFX version 12.1. However, it seems that CFX does not provide Temperature. gradient X etc values like it provides for other variables likes velocities and enthalpy. I have tried using the option `Selected Variables` in Output control along with `All` selected for Output variable operators and ensuring Temperature to be in the `Output Variable list`. This according to the documentation should give be gradient values for temperature. But still CFX post does not show any such variable in the result file. Is there anything else which I should try? Otherwise CFX Post shows gradient values for static enthalpy as variables (Static ethalpy. Gradient X and so on). The fluid in my simulations is liquid water. I think I can get approximate values of temperature gradients by dividing the enthalpy gradient values by local value of cp of water ( I am using temperature dependent properties). This will amount to assuming that the water static enthalpy is only a function of temperature which I think is an ok assumption for liquid water. Do you think that this approach is correct?

July 11, 2011, 08:16		#4
noslip New Member Join Date: Jan 2011 Posts: 22 Rep Power: 15	temperature gradients are not automatically generated in cfx. you can generate gradients of any (meaningful) scalar variables in post. create a new variable in the "variables" tab, set method from "expression" to "gradient" and select the variable you like (in your case the temperature). this works in 12.1 btw. hope this helps vstram likes this.

July 11, 2011, 09:21		#5
Chander Senior Member Join Date: Oct 2010 Location: Zurich Posts: 176 Rep Power: 16	Thanks a lot Glenn and noslip. This is very helpful. I wonder why it is not mentioned in the documentation for CFX-Post. You have been a great help!! Last edited by Chander; July 11, 2011 at 10:04.

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July 11, 2011, 05:18		#2
Chander Senior Member Join Date: Oct 2010 Location: Zurich Posts: 176 Rep Power: 16	Anyone please ?

July 11, 2011, 07:31		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,852 Rep Power: 144	Maybe you should upgrade to V13. I think it has full support for variable spatial derivatives. But I thought V12 had derviatives on temperature anyway. Are you sure it is not built in?