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Time average results in Transient CFX Simulation

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Old   November 14, 2011, 04:25
Question Time average results in Transient CFX Simulation
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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.

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Old   November 14, 2011, 06:20
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Did you use the transient statistics option? What makes you think the arithmetic average did not work?
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Old   November 14, 2011, 07:07
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Originally Posted by ghorrocks View Post
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~
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File Type: jpg transient.jpg (44.2 KB, 284 views)
File Type: jpg average.jpg (41.3 KB, 243 views)
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Old   November 14, 2011, 07:13
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Sijal Ahmed Memon (turboenginner@gmail.com)
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good work. well done
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Old   November 16, 2011, 07:23
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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.
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Old   November 16, 2011, 08:18
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makes any difference ?
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Old   October 10, 2012, 13:42
Default time avrage
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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
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Old   October 11, 2012, 09:55
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Just activate "Transient Statistics" under the "output control->TrnStats" in CFX Pre.
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Old   October 23, 2012, 03:31
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I dont know how can i find avrage result in post cfd.
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Old   October 24, 2012, 11:42
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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"
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Old   October 28, 2012, 23:33
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thank you so much.
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Old   December 26, 2012, 03:05
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Quote:
Originally Posted by monkey1 View Post
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
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Old   December 27, 2012, 18:52
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Quote:
Originally Posted by wertyfg View Post
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).
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Old   January 8, 2013, 05:05
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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.
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Old   January 28, 2013, 11:43
Default Heat flux time average in CFX
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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
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Old   July 14, 2014, 16:03
Default No change in transient results in CFX
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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
Attached Images
File Type: jpg 0.jpg (22.4 KB, 30 views)
File Type: jpg 01.jpg (25.5 KB, 37 views)
File Type: jpg 05.jpg (25.5 KB, 31 views)
File Type: jpg 1.jpg (25.5 KB, 29 views)
File Type: jpg 2.jpg (25.5 KB, 28 views)
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Old   July 14, 2014, 18:22
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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
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Old   May 29, 2015, 09:50
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Quote:
Originally Posted by k.vafiadis View Post
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?
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Old   May 29, 2015, 11:14
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Quote:
Originally Posted by Mina_Shahi View Post
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
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Old   June 1, 2015, 04:35
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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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