Problem about 'Residual', 'Drift', 'CFL number'.

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xingjian
Posts: 55
Joined: Thu Apr 06, 2017 12:34 pm

Problem about 'Residual', 'Drift', 'CFL number'.

Post by xingjian »

Hello,

This time I simulate the total nozzle, all the boundary conditions are reasonable, and I calculated it with CS 5.0.1 with Windows.

Here is my problem, because the new version has the file 'residual.csv' in the directory 'RESU', so I opened it with ParaVis:
4.PNG
It seems very stable, then I zoom in it:
2.PNG
It's very stable, but why the residual of 'k' is 62, 'velocity' is 40, 'pressure' is 16, are they too large as residuals?

At the same time, I saw the file 'listing':
0.png
Residuals are 10E-04, E-05 or E-06, why they are not corresponding with the 'residual.csv'

And what's the 'Drift'? Is it 'Derive'?

Is it convergent or not?

Best Regards

XING Jian
xingjian
Posts: 55
Joined: Thu Apr 06, 2017 12:34 pm

Re: Problem about 'Residual', 'Drift', 'CFL number'.

Post by xingjian »

And for 'CFL number', it is 'Courant number'?

CFL=U*Dt/Dx with U is with U is characteristic velocity, Dx is characteristic length.
Fo=v*Dt/Dx^2 with v is viscosity, Dx is characteristic length.

I want to obtain the maximum CFL and Fourier, I chose the fastest, and the mesh is the finest area. Dx=0.0008, U=23, v=2*10^5.

So CFL=2.8*10^4*Dt

So Fo=31.25*Dt

For most case, CFL number is around 1 ~ 5, so I chose Dt = 1*10^-5, CFL =0.28, Fo=0.0003125. So I take Max CFL=1, Max Fo=1.

Here is results:
Fourier NB:
5.PNG
Fourier number is no problem.
Courant NB:
1.PNG
According to the trend, the Courant number will continue to increase but it is limited to 1. Should I increase the limitation? But this does not conform to the theory.

So what should I do?

Thank you very much

Best Regards

XING Jian
Yvan Fournier
Posts: 4070
Joined: Mon Feb 20, 2012 3:25 pm

Re: Problem about 'Residual', 'Drift', 'CFL number'.

Post by Yvan Fournier »

Hello,

If your test case is small, could you post it ? Or at least post the listing, setup.log, and residuals.csv.

Regards,

Yvan
xingjian
Posts: 55
Joined: Thu Apr 06, 2017 12:34 pm

Re: Problem about 'Residual', 'Drift', 'CFL number'.

Post by xingjian »

Thank you Yvan.

Here are 'XML', 'residual.csv' and 'listing'. Is my residual of the 'residual.csv' incorrect? They are should be 10E-03(or E-04;E-05) like 'Norm. Residual' in 'listing'?

And for the 'Courant Nb', 'Max CFL Nb', should I increase it?

Best Regards

XING Jian
Attachments
listing.zip
(344.97 KiB) Downloaded 304 times
residuals.csv
(91.2 KiB) Downloaded 284 times
upwind_CFL1_Fo1_0.00001.xml
(20.08 KiB) Downloaded 347 times
Yvan Fournier
Posts: 4070
Joined: Mon Feb 20, 2012 3:25 pm

Re: Problem about 'Residual', 'Drift', 'CFL number'.

Post by Yvan Fournier »

Hello,

The residuals in the csv file seem to match the "time residuals" and not the "normalized residuals" from the listing file. I'll check how this is measured/which type of norm is used.

Regards,

Yvan
xingjian
Posts: 55
Joined: Thu Apr 06, 2017 12:34 pm

Re: Problem about 'Residual', 'Drift', 'CFL number'.

Post by xingjian »

Hello Yvan,

So how can I solve it? Actually I use CS5.0.1 now, maybe I try it with 5.0.0?

Best Regards

XING Jian
Robert
Posts: 26
Joined: Mon May 22, 2017 11:14 am

Re: Problem about 'Residual', 'Drift', 'CFL number'.

Post by Robert »

Hello,

Sorry for reviving an old thread but after all how are those norm. residuals and time residuals measured? I'm using version 5.0 for windows and the Convergence tool doesn't work( I also tried to run it from a terminal with no results with code_saturne trackcvg). If there are no monitoring points added, which one is better to use for convergence tracking?

Regards,
Robert
valentin.derrien
Posts: 12
Joined: Fri Feb 23, 2018 2:28 pm

Re: Problem about 'Residual', 'Drift', 'CFL number'.

Post by valentin.derrien »

Hello,

I am facing the same problem as Xing Jian : my residuals.csv values are a way greater than my listing values.

Did you find a solution ? Which ones should I use for convergence test ?

Regards,
Valentin
Yvan Fournier
Posts: 4070
Joined: Mon Feb 20, 2012 3:25 pm

Re: Problem about 'Residual', 'Drift', 'CFL number'.

Post by Yvan Fournier »

Hello,

The values in the CSV file match the last column in the listing (time residual, and not normalized residual). I'm not sure there is much theoretical documentation about that, but I'll try to get more info on how to interpret that value.

Regards,

Yvan
valentin.derrien
Posts: 12
Joined: Fri Feb 23, 2018 2:28 pm

Re: Problem about 'Residual', 'Drift', 'CFL number'.

Post by valentin.derrien »

Hello,

Thank you for your quick answer.

Could you please technically explain what are the norm.residual, drift and time residual and which one should be used for convergence observation in the case of not using monitoring points ?

Best regards,

Valentin
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