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 BalanceChen November 14, 2011 04:25

Time average results in Transient CFX Simulation

Hi my friends, I am doing a transient simulation using CFX and my question is how can I get a time average flow field of simulation. I tried to use the Arithmetic Average in CFX Output Control. But the results seems not right. Who can help me out? Thank you very much.

BalanceChen

 ghorrocks November 14, 2011 06:20

Did you use the transient statistics option? What makes you think the arithmetic average did not work?

 BalanceChen November 14, 2011 07:07

2 Attachment(s)
Quote:
 Originally Posted by ghorrocks (Post 331972) Did you use the transient statistics option? What makes you think the arithmetic average did not work?
Yes, I use the transient statistics option.

I am doing a transient simulation of turbomachinery and the inflow is not uniform circumferentially. The instantaneous total pressure at the rotor inlet is distorted as it should be, but the arithmetic average not. Please refer to the attachment for more information. Thank you very much~

 Far November 14, 2011 07:13

good work. well done

 BalanceChen November 16, 2011 07:23

I have just found the trouble spot~

As for the transient turbomachinery simulation, a time-average results is time averaged over passage but not over the whole machine. I made a mistake to average over the whole machine to destroy the circumferential distortion.

 Far November 16, 2011 08:18

makes any difference ?

time avrage

hello,

I am doing transient problem and I am gonna do time avrage for velocity . can you tell me how can I do it?

Best regards

 monkey1 October 11, 2012 09:55

Just activate "Transient Statistics" under the "output control->TrnStats" in CFX Pre.

I dont know how can i find avrage result in post cfd.

 monkey1 October 24, 2012 11:42

You just select in CFX Post the "Velocity.TrnAvg" Variable to be displayed (on a Plane for example). Then you will see the time averaged Velocity.
All time averaged Variables are named like this "Variablename.TrnAvg"

Thanks

thank you so much.

 wertyfg December 26, 2012 03:05

Quote:
 Originally Posted by monkey1 (Post 388331) You just select in CFX Post the "Velocity.TrnAvg" Variable to be displayed (on a Plane for example). Then you will see the time averaged Velocity. All time averaged Variables are named like this "Variablename.TrnAvg"
But if I want the average velocity in one specific period, how can I do? Thank you

Quote:
 Originally Posted by wertyfg (Post 399031) But if I want the average velocity in one specific period, how can I do? Thank you
Hello, you got to specify this time period (start averaging time - end averaging time).

 monkey1 January 8, 2013 05:05

If you want a time average for a specified period only you will have to determine the start and end iteration during your calculation run and specify them as start and end iteration in CFX Pre for the definition of the Transient statistics....
Unfortunately I never discovered an option to specify a start and end TIME...only iteration loops.

 alinik January 28, 2013 11:43

Heat flux time average in CFX

Hi,

I want to find out the time average Heat flux on a surface in CFX. I have activated Arithmetic avg in trn stats in CFX Pre but there is no sign of Heat flux.Trnavg in the result variables. Can somebody please help me with this issue?

Thanks

 hesamking July 14, 2014 16:03

No change in transient results in CFX

5 Attachment(s)
I am doing the supersonic flow over a forward facing step and
it's a transient simulation. Actually it converges after 50-60 iterations. (the momentum components).
The problem is when i go to CFD post and check the results I don't see any difference between the results from the very written result (i have them written every 0.1 s) till the 2 seconds that is the end of simulation. I have tried very fine mesh and regular mesh and I know the mesh is fine. The boundary conditions are followed as the problem descrpition. my timestep is 1e-4.
My friend got reasonable results with the same mesh size and BC in OpenFoam and saw the shocks developing overtime and detach.
Mine, on the other hand, just shows the detachment of the shock from the very first step till the last one as if it is steady!!!!
I have attached the pictures for 0, 0.1 (first), 0.5, 1, and 2.
I would appreciate the help
Best,
Hesam

 ghorrocks July 14, 2014 18:22

You have too much dissipation in your model and it is causing the small flow features to disappear. You will need:
* Finer mesh (do a mesh sensitivity study)
* Finer time step (do a time step sensitivity study)
* High order differencing (High Res is probably best)
* Dynamic mesh refinement at the shocks would help

 Mina_Shahi May 29, 2015 09:50

Quote:
 Originally Posted by k.vafiadis (Post 399256) Hello, you got to specify this time period (start averaging time - end averaging time).
Hi, I haven't specify it in pre, is there any way to do it in cfx post?

 alinik May 29, 2015 11:14

Quote:
 Originally Posted by Mina_Shahi (Post 548184) Hi, I haven't specify it in pre, is there any way to do it in cfx post?
Mina,

I dont think that is possible. I had same problem and I ended up resolving the case.
By the way is there anyway to define the model in a way that it does the transient averaging only over a portion of the total simulation time?

Thanks,
Ali

 Thomas MADELEINE June 1, 2015 04:35

well if you start and end the averaging in transient result it should average over the time specified, isn't it ?

You can always create an expression with the step function to get a non-zero result only during the time you want. then try an integration
it is a gross solution, but a solution anyway

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