How many time-steps are included in each .dat file for Fluent transient simulations?

nvarma · March 30, 2015, 16:36

I just discovered the hard way that fluent .dat written using the autosave function after particular intervals (every 40 iterations here) store different number of time steps.

This is quite annoying.

For instance results written at 480 iterations contain times 320, 360,400, 440 and 480.

Results written, at 360 only have 360 and 320.

Results written at 320 have, 320,280 and 240?

Why are the .dat files so inconsistent? I noticed this only after I imported them to CFDpost.

Thanks for reading.

nvarma · April 2, 2015, 08:45

I figured out a few other ways to track and write down the transient results but this still bothers me.

Anyone got any idea what determines the number of time steps in a fluent dat file written during calculation?

LuckyTran · April 3, 2015, 00:01

I did not think it was ever possible for Fluent to save data from old time-steps in a single .dat file since the .dat file should contain only data of the current state.

If you are running transient simulation with 1st order backward differencing, then naturally the .dat file will contain data at the current time-step plus the previous time-step.

If you are running 2nd order, then the .dat file should contain the current time-step (n), the previous time-step (n-1), and the one before the previous time-step (n-2).

It shouldn't contain n-40 time-steps. I don't know how that happens.

nvarma · April 3, 2015, 08:45

Right? I am confused as well. I was using Tecplot all my life but recently had to switch to CFDpost. So post-proc of transient simulations is a pain.

Anyway this is what I get when I import ONE timestep dat. Different timestep dat files have different number of timesteps stored and it's completely random.

temp1.PNG

attiquejavaid08 · September 20, 2016, 14:27

did you find solution to this problem?

March 30, 2015, 16:36	How many time-steps are included in each .dat file for Fluent transient simulations?	#1
nvarma Senior Member nm Join Date: Mar 2013 Posts: 100 Rep Power: 13	I just discovered the hard way that fluent .dat written using the autosave function after particular intervals (every 40 iterations here) store different number of time steps. This is quite annoying. For instance results written at 480 iterations contain times 320, 360,400, 440 and 480. Results written, at 360 only have 360 and 320. Results written at 320 have, 320,280 and 240? Why are the .dat files so inconsistent? I noticed this only after I imported them to CFDpost. Thanks for reading.

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April 2, 2015, 08:45		#2
nvarma Senior Member nm Join Date: Mar 2013 Posts: 100 Rep Power: 13	I figured out a few other ways to track and write down the transient results but this still bothers me. Anyone got any idea what determines the number of time steps in a fluent dat file written during calculation?

April 3, 2015, 00:01		#3
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 65	I did not think it was ever possible for Fluent to save data from old time-steps in a single .dat file since the .dat file should contain only data of the current state. If you are running transient simulation with 1st order backward differencing, then naturally the .dat file will contain data at the current time-step plus the previous time-step. If you are running 2nd order, then the .dat file should contain the current time-step (n), the previous time-step (n-1), and the one before the previous time-step (n-2). It shouldn't contain n-40 time-steps. I don't know how that happens.

April 3, 2015, 08:45		#4
nvarma Senior Member nm Join Date: Mar 2013 Posts: 100 Rep Power: 13	Right? I am confused as well. I was using Tecplot all my life but recently had to switch to CFDpost. So post-proc of transient simulations is a pain. Anyway this is what I get when I import ONE timestep dat. Different timestep dat files have different number of timesteps stored and it's completely random. temp1.PNG

September 20, 2016, 14:27		#5
attiquejavaid08 Member Attique Javaid Join Date: Apr 2015 Location: Pakistan Posts: 66 Rep Power: 11	did you find solution to this problem?