[walakaka]

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

[walakaka]

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

[Tobi]

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.

[walakaka]

Originally Posted by Tobi

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!

[Tobi]

Actually you should not put it to the validation cases read the purpose of that forum

I confirm, it confuses a bit

[Santiago]

Originally Posted by walakaka

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"

[kalle]

From https://en.wikipedia.org/wiki/Lamina...ent_transition

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.

[Tobi]

Originally Posted by Santiago

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

[Santiago]

Originally Posted by kalle

From https://en.wikipedia.org/wiki/Lamina...ent_transition

"If not much care is taken, when running your simulation, you can arrive to Re=10^8 and still not get turbulence"

-- Santiago