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-   -   Time domain analysis of Unsteady Flow (https://www.cfd-online.com/Forums/fluent/41969-time-domain-analysis-unsteady-flow.html)

Nikunj Raghuvanshi August 8, 2006 21:29

Time domain analysis of Unsteady Flow
 
Hi guys, I am doing an unsteady turbulent LES simulation in Fluent for the interior of a Flute. I autosaved the data for each timestep and want to analyze the vorticity at the cell centers as a function of time.

Question 1: All of fluent's post-processing tools seem to be geared towards analyzing the flow data at a given time, not analyzing the data in time domain. Is there any easy way in Fluent to do any kind of time-domain analysis for unsteady simulations?

Question 2: How do I get fluent to store the vorticity at the cell centers in the data file along with the rest of the stuff. Is there any way at all to control what all fluent stores in its data file? What all does it store in the data file by default? The Fluent manual only says it stores the "flow variables" in the data file, which is pretty vague.

The only solution that I can think of rite now is to somehow get Fluent to store the vorticity at the cell centers in the data files, then write my own code to parse these data files, collect the vorticity information at the cell centers at different time steps and then do the analysis in my code. Of course, this is tedious and Fluent is very much capable of doing it for me.

Is there any easier way? _Absolutely_ any suggestions are welcome. Sorry for the long mail.

thanks a ton, -Nikunj. --

Nikunj Raghuvanshi August 10, 2006 02:30

Re: Time domain analysis of Unsteady Flow
 
OK, I found how to go about doing what I wanted. I am posting the reply for the benefit of someone who runs into the same problem in the future.

There are no nice toold in fluent to do good time-domain analysis. And using autosave to store everything carries a HUGE space penalty. Anyway, if you're ready to do that, then: METHOD 1: THe easy way to do it is to use a UDF, specifically, the DEFINE_RW_FILE DEFINE, which gives the user specific control over what will be stored in the .dat file along with what Fluent stores by default. As to exactly what variables Fluent stores in .dat files by default, I don't know the answer, but that can be (painfully) gathered by reading the detailed file format in the users manual.

METHOD 2: Don't use autosave at all. Don't save the data files at all. Just use the EXECUTE_AT_END DEFINE and create your own file and write the relevant flow variables into the created file at each timestep. This gives you exactly the data you need. No painful Fluent .dat parsing and no space penatly. This is what I am going to do.

-Nikunj.


ssixr December 25, 2012 14:09

Quote:

Originally Posted by Nikunj Raghuvanshi
;134826
OK, I found how to go about doing what I wanted. I am posting the reply for the benefit of someone who runs into the same problem in the future.

There are no nice toold in fluent to do good time-domain analysis. And using autosave to store everything carries a HUGE space penalty. Anyway, if you're ready to do that, then: METHOD 1: THe easy way to do it is to use a UDF, specifically, the DEFINE_RW_FILE DEFINE, which gives the user specific control over what will be stored in the .dat file along with what Fluent stores by default. As to exactly what variables Fluent stores in .dat files by default, I don't know the answer, but that can be (painfully) gathered by reading the detailed file format in the users manual.

METHOD 2: Don't use autosave at all. Don't save the data files at all. Just use the EXECUTE_AT_END DEFINE and create your own file and write the relevant flow variables into the created file at each timestep. This gives you exactly the data you need. No painful Fluent .dat parsing and no space penatly. This is what I am going to do.

-Nikunj.

hi Nikunj,
i am also trying to figure out how to extract out of huge data files...the method you have mention above are to store the data whichever we anticipated. sometimes we need analysis to some random hotspots like shocks in our analysis. how to extract pressure variation over the time at the specified location with all my data files. is there a way to make connection between all data files and extract whatever data we wanted? please let me know ....


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