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Why is the SimpleFoam Laminar solver Valid for Re3000

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Old   February 28, 2018, 14:54
Default Why is the SimpleFoam Laminar solver Valid for Re3000 [solved]
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Shafik Walakaka
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Hi everyone,

I am currently validating a pipeflow simulation (Single-phase). I aim to validate laminar flows first (RAS turned off in pimpleFoam) for Re300 to Re2400.

When the Re gets high enough (approximately past Re2000), I expect the results to stop converging (with RAS turned off) as the flow is no longer laminar.

However, I obtained excellent results when compared to the H-P equation for my flow at Re3000.

My pipe is of length 20m, Diameter 0.0563m. Any if this result is expected?

Regards
Shafik

Last edited by walakaka; March 7, 2018 at 15:55. Reason: solved
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Old   March 1, 2018, 08:56
Default R3500 is valid against H-P too? What's wrong
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Hi everyone!

My velocity profile for Re3500 is also valid against the H-P equation using laminar PIMPLE solver in openfoam. Does anyone have any idea what I'm doing wrong?

Pipe is 20m long and 0.0563m Dia.

Attached is the image of the developed velocity profile!

Regards
Shafik
Attached Images
File Type: png Re3500_vel_profile_18m.PNG (64.9 KB, 18 views)

Last edited by walakaka; March 1, 2018 at 09:56.
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Old   March 7, 2018, 09:26
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Hi,

first of all. Please read the purpose of the subforums.
Why shouldn't pimpleFoam be not valid for such Reynolds numbers? If you solve in 'laminar' mode, you are using the Navier-Stokes equations without any assumptions. It is like DNS. The fluid itself follows the Navier-Stokes equations so why should there be a problem. If you mesh if fine, you probably resolve everything.
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Old   March 7, 2018, 15:55
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Quote:
Originally Posted by Tobi View Post
Hi,

first of all. Please read the purpose of the subforums.
Why shouldn't pimpleFoam be not valid for such Reynolds numbers? If you solve in 'laminar' mode, you are using the Navier-Stokes equations without any assumptions. It is like DNS. The fluid itself follows the Navier-Stokes equations so why should there be a problem. If you mesh if fine, you probably resolve everything.
Thank you for your reply. And I do apologize, I should've posted this in the validation section of the forum.

Thanks again!
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Old   March 7, 2018, 17:58
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Actually you should not put it to the validation cases read the purpose of that forum

I confirm, it confuses a bit
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Old   March 8, 2018, 07:31
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Quote:
Originally Posted by walakaka View Post
Hi everyone!

My velocity profile for Re3500 is also valid against the H-P equation using laminar PIMPLE solver in openfoam. Does anyone have any idea what I'm doing wrong?

Pipe is 20m long and 0.0563m Dia.

Attached is the image of the developed velocity profile!

Regards
Shafik
Just for the purpose of clarification before deleting this post: high Reynolds numbers do not generate turbulence, it only changes the character of NS as a quasi-linear system. Instabilities, and high enough Re, trigger turbulence. This is true in the "real world" as it is in the "numerical world"
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Old   March 8, 2018, 08:30
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From https://en.wikipedia.org/wiki/Lamina...ent_transition

Quote:
Reynolds found that the transition occurred between Re = 2000 and 13000, depending on the smoothness of the entry conditions. When extreme care is taken, the transition can even happen with Re as high as 40000. On the other hand, Re = 2000 appears to be about the lowest value obtained at a rough entrance.
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Old   March 8, 2018, 08:47
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Quote:
Originally Posted by Santiago View Post
Just for the purpose of clarification before deleting this post
The post is not deleted I just moved it. Thus, your answer will be here forever
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Old   March 8, 2018, 09:01
Default Look at me, I'm citing myself
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Quote:
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"If not much care is taken, when running your simulation, you can arrive to Re=10^8 and still not get turbulence"

-- Santiago

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