Fluent Iterating very slow

Sherif.farrag · May 3, 2020, 07:34

Hi,

I did 2D simulation on Ansys Fluent. iterating was very smooth and one iteration takes ~1sec as the mesh has 80 thousands elements.
I did the same model but 3D I got 6 Million elements and one iteration takes ~15 minutes. is that normal ? knowing that thousands of iterations are needed from my 2D experience with the model!
I have Intel Core i5 with 8 Gb Ram. Using parallel processing with 4 cores and single precision instead.
The model is a simple supersonic flow over rocket nozzle.
Any ideas? Is that normal?

vinerm · May 3, 2020, 17:12

For a 6 million cell count (assuming you mean cell count by element because element terminology is not used in FVM or Fluent), it in itself is a miracle that you are able to run it at all on an 8GB RAM machine. For a 8 GB RAM, if you are running single phase, turbulent flow, limit is 2 million for an optimum speed. 6 million cell count requires minimum 24 GB RAM for a optimum run. Speed is dependent on RAM speed and processor speed.

Sherif.farrag · May 3, 2020, 22:29

Thanks Vinerm for your help.
I've tried my friend's machine. It's Intel i7 with 16Gb Ram. it worked a lot faster. now one iteration takes ~6sec.
As you know now I have to take the results from my friends after finishing.
What is the best way to do that?
Taking the whole folder? or exporting data and open it with my CFD-Post?
Taking in consideration that he is using newer Ansys version than mine.
Also take in consideration that some times when I'm doing export a result and open in in CFD post independently it gives missing mesh error!
So, What is the best way to take the results?

vinerm · May 5, 2020, 10:20

If it is steady-state, then just take final case and data files and open those in CFD-Post. CFD-Post can open newer version data files as well. Mesh error comes only if case file is not available in the same directory. User does not need to load case file in CFD-Post but it must be available in the directory with the same name as that of data file that user loads in CFD-Post.

If it is transient, then better to export cdat files and a final set of case and data files.

May 3, 2020, 07:34	Fluent Iterating very slow	#1
Sherif.farrag New Member Join Date: May 2020 Posts: 2 Rep Power: 0	Hi, I did 2D simulation on Ansys Fluent. iterating was very smooth and one iteration takes ~1sec as the mesh has 80 thousands elements. I did the same model but 3D I got 6 Million elements and one iteration takes ~15 minutes. is that normal ? knowing that thousands of iterations are needed from my 2D experience with the model! I have Intel Core i5 with 8 Gb Ram. Using parallel processing with 4 cores and single precision instead. The model is a simple supersonic flow over rocket nozzle. Any ideas? Is that normal?

May 3, 2020, 17:12	Speed of calculation	#2
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 36	For a 6 million cell count (assuming you mean cell count by element because element terminology is not used in FVM or Fluent), it in itself is a miracle that you are able to run it at all on an 8GB RAM machine. For a 8 GB RAM, if you are running single phase, turbulent flow, limit is 2 million for an optimum speed. 6 million cell count requires minimum 24 GB RAM for a optimum run. Speed is dependent on RAM speed and processor speed. Sherif.farrag likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

May 5, 2020, 10:20	Case	#4
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 36	If it is steady-state, then just take final case and data files and open those in CFD-Post. CFD-Post can open newer version data files as well. Mesh error comes only if case file is not available in the same directory. User does not need to load case file in CFD-Post but it must be available in the directory with the same name as that of data file that user loads in CFD-Post. If it is transient, then better to export cdat files and a final set of case and data files. Sherif.farrag likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

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May 3, 2020, 22:29		#3
Sherif.farrag New Member Join Date: May 2020 Posts: 2 Rep Power: 0	Thanks Vinerm for your help. I've tried my friend's machine. It's Intel i7 with 16Gb Ram. it worked a lot faster. now one iteration takes ~6sec. As you know now I have to take the results from my friends after finishing. What is the best way to do that? Taking the whole folder? or exporting data and open it with my CFD-Post? Taking in consideration that he is using newer Ansys version than mine. Also take in consideration that some times when I'm doing export a result and open in in CFD post independently it gives missing mesh error! So, What is the best way to take the results?