CEL expression for normalizing temperature in CFX pre

shahpar73 · May 25, 2017, 04:48

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, 08:22

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, 04:48	CEL expression for normalizing temperature in CFX pre	#1
shahpar73 Member Shahid Parvez Join Date: Jul 2009 Location: Pakistan Posts: 38 Rep Power: 17	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)

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
CFX Pre & Post Startup Error	vigges	CFX	12	March 17, 2023 04:30
Writing expression in CFX Pre using Cell Volume	debabrata.mahapatra	CFX	1	July 21, 2014 09:51
What is the CEL expression for the logical command 'else if' in CFX pre	Anna Tian	CFX	1	June 26, 2013 13:21
CFX Expression Language help	JuPa	CFX	3	April 21, 2013 08:46
Temperature dependent thermal property in CFX	Subhadeep	CFX	5	March 22, 2012 02:52

May 25, 2017, 08:22		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	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.