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-   -   simplefoam straight and curved pipe validation (https://www.cfd-online.com/Forums/openfoam-verification-validation/129905-simplefoam-straight-curved-pipe-validation.html)

 jasxxx February 15, 2014 18:47

simplefoam straight and curved pipe validation

hi
does anyone have any simplefoam straight and curved pipe examples they can share.
any validation with test or theory for laminar and turbulent flows would be good.
i'm relatively new to CFD and openfoam, so would like to get the actual files so i can play with the mesh, etc for myself.
particularly interested in turbulence models comparisons, mesh studies for boundary layers, etc.
thanks
jas

 xxxx April 18, 2014 16:43

Dear jasxxx,

it seems to me that people are loosing their reason. CFD is a potentially powerful tool, but it has to be used with common sense.
Be aware that your asking for two test cases that are among the most known and experimented phenomena in fluid dynamics. For what concern losses in a straight pipe, just have a look to Moody's diagramm. Concerning the curved pipe, just open a "Fluid Mechanics" or "Hydraulics" book and look for head losses and flow field.
Never forget to think before you build a CFD model, and ask yourself if you really need it.

Sincerely,

F.F.

 alexeym April 18, 2014 17:11

Dear F.F.,

I guess jasxxx means validation of already built model (i.e. in OpenFOAM there are solvers and turbulence models), and yes, they can be compared to theoretical solutions. The only problem you can't just say "hey, I'd like to have a pipe with diameter 1 cm and length 1 m, and there is inflow of 1 cl/s, please tell me pressure at point (0.5 m, 0 m, 0 m)", you should build mesh first (or maybe build software first), set ICs and BCs and run simulation, post-process results.

Though maybe partly you are right, jasxxx should first go to \$FOAM_TUTORIALS and then specify exactly what's wrong with simpleFoam tutorials. As there are plenty of pipe meshes around and case files for simpleFoam.

 xxxx April 20, 2014 10:05

Hello.

I don't want to seem arrogant, but what jasxxx actually asked for is
Quote:
 any validation with test or theory for laminar and turbulent flows
.
What do you mean for validation? What I mean is to compare numerical results with experimental/theoretical ones and see if an agreement can be found.
What is validation for the flow in a straight pipe?
1- global quantities: verify if head losses are well predicted. ( -> Moody's diagramm)
2- local quantities: verify if the velocity profile (i.e. velocity plot vs radial distance from the pipe axis) looks at it should be: parabolic for laminar flow, log law + const value in the bulk for turbulent flow (*). ( -> see any book dealing with Hydraulics)
Who cares about velocity/pressure at the point (0.5;0;0) ? Please, have a bit of physical sense..

(*) Note that if you're using wall function, this is imposed and so it true a priori.

What jasxxx is doing is what anyone has done at the beginnig (or at least should have done). But we don't need CFD models to validate CFD models!!!
What we need is (real) physics, and it is either in our minds our it comes from experiments, not from CFD.

Regards.

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