Fluent running increadibly slow

MayTheFlowBeWithYou · July 10, 2017, 05:14

Dear cfd-online community,

When I run serial simulations of fluent, sometimes the simulations will run very slow for no reason. The difference is quite extreme, a simulation that takes only 2 min to complete when it is running fast will take over 3 hours when it is running slow. And this is for literally the same simulation.

The only differences I have been able to notice between when fluent is slow and when fluent is fast are:
- when it is fast it does mostly not show the mesh.
- when it is slow, the cores are basically idle.

Clearly the last point is the key here, but I have no clue why fluent would not maximize its use of one of the cores. I even put the priority for all its processes on "realtime", this makes no difference.

The amount of other programs I have on also does not seem to influence it.

If anyone has any idea about what might cause fluent to run slower sometimes I would really like to hear it.

For extra information, I have these two screenshots of the taskmanager during times when fleunt is slow and when it is fast (both run the exact same simulation):

FAST:

SLOW:

P.S. Currently, I "fix" the problem by just restarting the pc until fluent runs fast. It's kind of like a game of CPU-roulette at this point.

Foxhunter · November 3, 2017, 10:17

Do you use the parallel solver?

MayTheFlowBeWithYou · November 3, 2017, 12:09

No, everything was in series.

Foxhunter · November 6, 2017, 03:43

Quote:

Originally Posted by MayTheFlowBeWithYou

No, everything was in series.

I am quite new to Fluent, but running the program in Parallel with the number of processes equal to the cores of my CPU kept the program running at 100% all the time. When I use series it sometimes goes a bit idle. Maybe it's something to fiddle with

bhanumahesh1993 · November 6, 2017, 15:09

Do u use the same mesh size in both the cases or different?

MayTheFlowBeWithYou · November 6, 2017, 17:40

Quote:

Originally Posted by Foxhunter

I am quite new to Fluent, but running the program in Parallel with the number of processes equal to the cores of my CPU kept the program running at 100% all the time. When I use series it sometimes goes a bit idle. Maybe it's something to fiddle with

My simulation can't be run in parallel. This is also not the cause of the problem, the entire program is slower, including loading its own UI and stuff.

MayTheFlowBeWithYou · November 6, 2017, 17:41

Quote:

Originally Posted by bhanumahesh1993

Do u use the same mesh size in both the cases or different?

In both cases I run exactly the same simulation. With 'exactly', I literally mean exactly.

bhanumahesh1993 · November 6, 2017, 19:22

Quote:

Originally Posted by MayTheFlowBeWithYou

In both cases I run exactly the same simulation. With 'exactly', I literally mean exactly.

Generally speaking,
Laptops shows high performance in charging mode and low performance in battery mode. It's actually a system setting in many laptops. Do u observe the same case?
I mean, ansys run faster during charging!

MayTheFlowBeWithYou · November 7, 2017, 07:34

Quote:

Originally Posted by bhanumahesh1993

Generally speaking,
Laptops shows high performance in charging mode and low performance in battery mode. It's actually a system setting in many laptops. Do u observe the same case?
I mean, ansys run faster during charging!

I am aware of this and I have set my laptop to use as much resources as it has while connected to a power outlet. In both cases the laptop was charging. The only thing between the two cases is restarting it. Where the "fast" case ran first, and the "slow" was after restarting. I ran these two simulations specifically for testing performance so all variables were kept the same as much as possible.

Bigburd2323 · April 25, 2018, 16:02

I have experience the exact same thing, it is very annoying. Did you ever find the source of the problem?

MayTheFlowBeWithYou · April 26, 2018, 08:07

Unfortunately, I have never found the source. Currently, I don't do CFD work anymore so I don't think I will either.

Gert-Jan · April 26, 2018, 08:21

So the flow isn't with you anymore?
Then I hope you're in material science now, otherwise flows will be chasing you.

andreasydney · May 22, 2018, 03:04

I have exaclty the same problem, someone can help me?it is very annoying and is impossible to work in this situation...i have already tried to install a second time Ansys but nothing change..one week ago was fast and now is incredibly slow and i can't work..not only run a simulation but even look at the graphics..i don't know what can i do..

July 10, 2017, 05:14	Fluent running increadibly slow	#1
MayTheFlowBeWithYou Member I have to remain anonymous, I'm sorry. Join Date: Jun 2017 Location: The Netherlands, Delft University of Technology Posts: 48 Rep Power: 9	Dear cfd-online community, When I run serial simulations of fluent, sometimes the simulations will run very slow for no reason. The difference is quite extreme, a simulation that takes only 2 min to complete when it is running fast will take over 3 hours when it is running slow. And this is for literally the same simulation. The only differences I have been able to notice between when fluent is slow and when fluent is fast are: - when it is fast it does mostly not show the mesh. - when it is slow, the cores are basically idle. Clearly the last point is the key here, but I have no clue why fluent would not maximize its use of one of the cores. I even put the priority for all its processes on "realtime", this makes no difference. The amount of other programs I have on also does not seem to influence it. If anyone has any idea about what might cause fluent to run slower sometimes I would really like to hear it. For extra information, I have these two screenshots of the taskmanager during times when fleunt is slow and when it is fast (both run the exact same simulation): FAST: SLOW: P.S. Currently, I "fix" the problem by just restarting the pc until fluent runs fast. It's kind of like a game of CPU-roulette at this point. Last edited by MayTheFlowBeWithYou; July 13, 2017 at 04:17.

November 3, 2017, 12:09		#3
MayTheFlowBeWithYou Member I have to remain anonymous, I'm sorry. Join Date: Jun 2017 Location: The Netherlands, Delft University of Technology Posts: 48 Rep Power: 9	No, everything was in series. __________________

April 26, 2018, 08:07		#11
MayTheFlowBeWithYou Member I have to remain anonymous, I'm sorry. Join Date: Jun 2017 Location: The Netherlands, Delft University of Technology Posts: 48 Rep Power: 9	Unfortunately, I have never found the source. Currently, I don't do CFD work anymore so I don't think I will either. __________________

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November 3, 2017, 10:17		#2
Foxhunter New Member Join Date: Oct 2017 Posts: 26 Rep Power: 9	Do you use the parallel solver?

November 6, 2017, 15:09		#5
bhanumahesh1993 New Member Bhanu Mahesh Join Date: Jul 2017 Posts: 6 Rep Power: 9	Do u use the same mesh size in both the cases or different?

April 25, 2018, 16:02		#10
Bigburd2323 New Member Francisco Join Date: Apr 2018 Posts: 1 Rep Power: 0	I have experience the exact same thing, it is very annoying. Did you ever find the source of the problem?

April 26, 2018, 08:21		#12
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,913 Rep Power: 28	So the flow isn't with you anymore? Then I hope you're in material science now, otherwise flows will be chasing you.

May 22, 2018, 03:04		#13
andreasydney New Member andrea robone Join Date: May 2018 Posts: 1 Rep Power: 0	I have exaclty the same problem, someone can help me?it is very annoying and is impossible to work in this situation...i have already tried to install a second time Ansys but nothing change..one week ago was fast and now is incredibly slow and i can't work..not only run a simulation but even look at the graphics..i don't know what can i do..