Transient heat flux

pkladisios · September 18, 2015, 11:05

Greetings, once more!

I seek your advice on a perplexing matter. I wish to apply a transient heat flux on one of the walls of my simulating domain. Could you explain to me what must i do?

Thank you in advance!

Opaque · September 18, 2015, 11:42

what kind of input do you have ?

For 1D transient data --> 1D Interpolation

For mathematical expression --> CEL

pkladisios · September 21, 2015, 04:33

I apologize for my delayed retort. I have a series of time-heat flux pairs that don't quite match my simulation's time steps. How could i insert them?

Edit
Opaque, your post actually pointed me to the right direction. I found the following thread that is pertinent to my query:
http://www.cfd-online.com/Forums/cfx...-function.html

In case someone else needs a summarized answer...

1.) In CFX-pre, define a new user function, thusly:
Option -> Interpolation (data input)
Argument units -> [s]
Result units -> [W/m^2]
Interpolation data -> Option -> One dimensional
We add manually all the pairs we want setting coordinate data (time in seconds) and result data (heat flux
in W/m^2).

2.) Next, define a new expression:
In the top bottom insert an expression and in the bottom box insert our newly defined user function.
Within the parentheses type t (function_name() should become function_name(t)). Apply.

3.) Edit the desired boundary condition.
Boundary details -> Heat transfer
Option -> Heat flux
Heat flux in -> Now instead of typing a number, activate the use of expressions (click on the square root a
icon) and enter the name of the expression, for instance my_expression.

I really hope it helps. Took my quite some time to figure it out. A following question would be this:
How can i import a supposedly massive amount of paired values? I assume my values must follow a specific format...

ghorrocks · September 21, 2015, 06:59

Use a 1D interpolation function.

evcelica · September 21, 2015, 14:01

Quote:

Originally Posted by pkladisios

How can i import a supposedly massive amount of paired values? I assume my values must follow a specific format...

Import them as a text file (I use excel, put everything in the first two columns, SAVE AS: "text, (tab delimited)". Import that in CFX Pre for you 1D interpolation function. Right click on the white box where the values are at, import.

pkladisios · September 22, 2015, 04:33

Got it!
I thank all of you!

nugh · December 14, 2015, 02:55

Please help...

I have a case with non linier heat flux in volume... heat flux following sinusoidal function or normal distribution function in volume.

How to make UDF (user defined function) on Fluent for my case..

ghorrocks · December 14, 2015, 05:27

The first step is to put the post on the right forum. Try the fluent forum. This is the CFX forum.

shadnia · December 31, 2015, 17:45

Hi Glenn
Thanks a lot for your kindly responses. I am applying the boundary conditions on CFX, so how can I write a CEL expression for having a non-linear heat flux (as a wall boundary condition) depending on both time and temperature? Thanks in advance and Happy new year

ghorrocks · January 2, 2016, 00:57

CEL expressions can be a function of anything you like. Have a look at the CFX tutorials for the basics of expressions.

September 18, 2015, 11:05	Transient heat flux	#1
pkladisios Member pkladisios Join Date: Jul 2015 Posts: 39 Rep Power: 11	Greetings, once more! I seek your advice on a perplexing matter. I wish to apply a transient heat flux on one of the walls of my simulating domain. Could you explain to me what must i do? Thank you in advance!

September 21, 2015, 04:33		#3
pkladisios Member pkladisios Join Date: Jul 2015 Posts: 39 Rep Power: 11	I apologize for my delayed retort. I have a series of time-heat flux pairs that don't quite match my simulation's time steps. How could i insert them? Edit Opaque, your post actually pointed me to the right direction. I found the following thread that is pertinent to my query: http://www.cfd-online.com/Forums/cfx...-function.html In case someone else needs a summarized answer... 1.) In CFX-pre, define a new user function, thusly: Option -> Interpolation (data input) Argument units -> [s] Result units -> [W/m^2] Interpolation data -> Option -> One dimensional We add manually all the pairs we want setting coordinate data (time in seconds) and result data (heat flux in W/m^2). 2.) Next, define a new expression: In the top bottom insert an expression and in the bottom box insert our newly defined user function. Within the parentheses type t (function_name() should become function_name(t)). Apply. 3.) Edit the desired boundary condition. Boundary details -> Heat transfer Option -> Heat flux Heat flux in -> Now instead of typing a number, activate the use of expressions (click on the square root a icon) and enter the name of the expression, for instance my_expression. I really hope it helps. Took my quite some time to figure it out. A following question would be this: How can i import a supposedly massive amount of paired values? I assume my values must follow a specific format... Last edited by pkladisios; September 21, 2015 at 07:01. Reason: solution, additional question

December 14, 2015, 02:55	Ask non linier heat flux in volume	#7
nugh New Member tri nugroho Join Date: Dec 2015 Posts: 2 Rep Power: 0	Please help... I have a case with non linier heat flux in volume... heat flux following sinusoidal function or normal distribution function in volume. How to make UDF (user defined function) on Fluent for my case..

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September 18, 2015, 11:42		#2
Opaque Senior Member Join Date: Jun 2009 Posts: 1,880 Rep Power: 33	what kind of input do you have ? For 1D transient data --> 1D Interpolation For mathematical expression --> CEL

September 21, 2015, 06:59		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Use a 1D interpolation function.

September 22, 2015, 04:33		#6
pkladisios Member pkladisios Join Date: Jul 2015 Posts: 39 Rep Power: 11	Got it! I thank all of you!

December 14, 2015, 05:27		#8
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	The first step is to put the post on the right forum. Try the fluent forum. This is the CFX forum.

December 31, 2015, 17:45		#9
shadnia New Member R-Sh Join Date: Oct 2014 Location: USA Posts: 23 Rep Power: 12	Hi Glenn Thanks a lot for your kindly responses. I am applying the boundary conditions on CFX, so how can I write a CEL expression for having a non-linear heat flux (as a wall boundary condition) depending on both time and temperature? Thanks in advance and Happy new year

January 2, 2016, 00:57		#10
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	CEL expressions can be a function of anything you like. Have a look at the CFX tutorials for the basics of expressions.