CEL expression for normalizing temperature in CFX pre

shahpar73 · May 25, 2017, 03:48

Hi
I am simulating a heat transfer problem in which I get temperatures on a plane surface varying from 300 [k] to 2700 [k].
For some reasons, I want to develop the following CEL expression in CFX-Pre;

Distance = 2[mm]*(T>=1750[K])/maxVal(T)@surface

i.e. I want to divide temperature which is equal to or greater than 1750 [k] by the maximum temperature on the surface and multiply by 2.

I tried but failed to "Evaluate" with the following error

ERROR
At least one operand of arithmetic operator is logical valued.
Error detected for '*' operator at position 2.

Can someone help please... (SOLVED, thanks)

ghorrocks · May 25, 2017, 07:22

You cannot arbitrarily change solver variables like that. Numerical solvers do not work that way.

If you want to manually set a temperature to a certain value then use a source term. Have a look in the CFX documentation on how to set source terms to set variables to specific values.

But I recommend this is VERY bad practise. You are getting crazy temperatures because either you have missed an important piece of physics or your simulation is numerically unstable. You should fix the missing physics or the instability to eliminate the problem, not try to patch over it as your suggestion would do.

May 25, 2017, 03:48	CEL expression for normalizing temperature in CFX pre	#1
shahpar73 Member Shahid Parvez Join Date: Jul 2009 Location: Pakistan Posts: 38 Rep Power: 16	Hi I am simulating a heat transfer problem in which I get temperatures on a plane surface varying from 300 [k] to 2700 [k]. For some reasons, I want to develop the following CEL expression in CFX-Pre; Distance = 2[mm](T>=1750[K])/maxVal(T)@surface i.e. I want to divide temperature which is equal to or greater than 1750 [k] by the maximum temperature on the surface and multiply by 2. I tried but failed to "Evaluate" with the following error ERROR At least one operand of arithmetic operator is logical valued. Error detected for '' operator at position 2. Can someone help please... (SOLVED, thanks)

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May 25, 2017, 07:22		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	You cannot arbitrarily change solver variables like that. Numerical solvers do not work that way. If you want to manually set a temperature to a certain value then use a source term. Have a look in the CFX documentation on how to set source terms to set variables to specific values. But I recommend this is VERY bad practise. You are getting crazy temperatures because either you have missed an important piece of physics or your simulation is numerically unstable. You should fix the missing physics or the instability to eliminate the problem, not try to patch over it as your suggestion would do.