CFD Online Discussion Forums

CFD Online Discussion Forums (
-   FLUENT (
-   -   Heat transfer in an unsteady-state simulation (

Raed141 August 7, 2009 02:21

Heat transfer in an unsteady-state simulation
Hey guys,

I would like to simulate an unsteady-state heat transfer problem in a square shape metal, in which the heat transfer from one side at high temperature to the opposite side which is at lower temperature. The other two sides have constant heat flux (0 w). I was able to prepare the mesh and run the simulation; the problem I am facing now is that I would like to plot the change in heat flux with respect to time. Someone suggested that I run the simulation for a period of time, find out the heat flux using the report, and then run it again. However, this is time consuming process, is there a faster way of doing it?
One more thing, if I would like to calculate the heat flux from the middle of the piece, how can I insert a line there?

Micael August 7, 2009 12:05

To monitor at each time step:
Solve -> Monitor -> Surface...

To create a line:
Surface -> Line/Rake

Check the user guide for details. What you want to do should be easy to do.


Raed141 August 7, 2009 12:59

Hi Mical,
Thank you for the advice, I was able to plot it; however, i would like to have the values numerically, because I have to divide these values on a constant. :)

Thank you again,

Micael August 7, 2009 13:37

Solve -> Monitor -> Surface
Select "Write"

Solve -> Monitor -> Surface -> Define
choose a name for your file (actually, there are already a default one)

Is that constant the surface area? If yes, may be you will have directly what you want by selecting "Area-Weighted Average" in Report Type.


Raed141 August 7, 2009 13:45

For the graph I am able to see it. For the writing, I would like to be able to use all the data (no, it is not the area) and input them in excel sheet. (I might get aroud 10000 points). So, I would like to have them in excel sheet, divide them on constant (i have many constants) then plot each as function of time.

Micael August 7, 2009 14:03

Open *.out file with Excel, that is not a problem. Also, you can cut-paste the content into a sheet (you may have to replace all spaces with tabs for that).

You have 10000 time steps!?

Raed141 August 7, 2009 14:13

O ok. I will try this and hopefully it will work.
About the time steps, I can make them around 600 time steps. But as you know about the unsteady-state, the first few seconds you should take them second by second, however, as time go on, you can increase the increment of time. So, if I am letting fluent to record, the time increment should be constant, so that's y :)

One more quick question: when i opened the file on excel sheet both values were in one cell :-s that's mean i have to separate them later?

Thank you so much! you are very helpful :)

Micael August 7, 2009 14:26

There are many way to separate the value. Two of them:

1- Open the file in notepad, Edit -> Replace..., replace all spaces with tabs (you have to paste the latter in the "Replace with" boxe (if you press tabs you exit the boxe)). Then you can copy-paste everything in Excel.

2- Open the file with Excel. This should open a wizard window. At the second step, choose "space" as separator.


Micael August 7, 2009 14:45

Note that you can control the time step with a UDF. It need not necessarily be constant.

Raed141 August 7, 2009 16:46

I am sorry but my knowledge with FLUENT is very limited, I am trying with this basic problem and facing lots of troubles. What is UDF? and how can I control the time step?
Is there specific tutorial for this?

Micael August 7, 2009 16:59

UDF = User Defined Function.

We write them in C language. They are simply C function, just like in C++ or other languages. UDF can incredibly increase the feature of Fluent. UDF really worth it to learn. Check the UDF user guide.

I faced lot of troubles when I started using Fluent. CFD modeling required a lot of learning to master.


Raed141 August 7, 2009 17:17

Ok, I check the guide time for now :D

Anyway, you have incredibly increasing my time efficiency in this problem :)

All times are GMT -4. The time now is 10:15.