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-   -   Inletoutlet (http://www.cfd-online.com/Forums/openfoam-solving/59287-inletoutlet.html)

rengu December 11, 2007 13:38

hi i use a simplefoam case
 
hi

i use a simplefoam case with a velocityinlet and a pressure outlet

i have see a lot topics about inletoutlet but i'm sorry to not understand

1/i've got sometimes a reverse flow in the outlet
i have to use an inletoutlet or an outletinlet?

if i would have got a reverse flow in the inlet?

2/for the inletoutlet,we've got to put inletoutlet for U,K,epsilon,R,nutilda and fixed value for p
is it the same if we use an outletinlet?

3/do we have got to put the same value between inletvalue & value or between outletvalue and value?


bestregards

eugene December 11, 2007 13:50

For an outlet that sometimes h
 
For an outlet that sometimes has inflow:

U:outlet
{
type inletOutlet;
inletValue uniform (0 0 0);
value uniform (0 0 0);
}

Note: this does not guarantee the inflow wont become unbounded.

Basically, inletOutlet is zero gradient unless the flow is inward in which case it is fixed value (inletValue). outletInlet is zero gradient if the flow is inward and fixed value (outletValue) if the flow is outward.

heavy_user May 10, 2010 08:24

Hey There,

I used this vor velocity Outlet conditions (i am supposed to do a simple jet-flame)
outlet
{
type inletOutlet;
inletValue uniform (0 0 0)
value zeroGradient;

}

My phi file after 1sec simulationtime shows inflow and outflow... :confused:
Is it the "value zeroGradient" that messes up or did I do anything else wrong?


Code:


    outlet
    {
        type            calculated;
        value          nonuniform List<scalar>
150
(
1.18479e-09
3.57232e-09
5.98072e-09
8.4018e-09
1.0827e-08
1.32471e-08
1.56525e-08
1.80329e-08
2.03774e-08
2.26741e-08
2.49105e-08
2.70731e-08
2.91473e-08
3.11175e-08
3.29669e-08
3.46772e-08
3.62291e-08
3.76015e-08
3.8772e-08
3.97166e-08
4.04096e-08
4.0824e-08
4.09312e-08
4.07016e-08
4.01047e-08
3.91097e-08
3.76862e-08
3.58065e-08
3.34439e-08
3.05774e-08
2.71942e-08
2.32919e-08
1.88829e-08
1.39957e-08
8.67884e-09
2.99631e-09
-4.29712e-10
-1.07772e-09
0
0
-1.65135e-09
0
-1.68011e-09
0
-1.6987e-09
0
-1.76071e-09
0
-1.87588e-09
0
0
-2.10134e-09
0
-2.26909e-09
-2.32623e-09
0
-2.53649e-09
-2.59421e-09
0
-2.79956e-09
-2.86481e-09
0
0
-3.19882e-09
-3.29259e-09
0
0
-3.73476e-09
-3.86297e-09
0
0
-4.45479e-09
-4.64113e-09
0
0
-5.3705e-09
-5.60678e-09
0
0
0
-6.73772e-09
-7.01818e-09
0
0
0
-8.31723e-09
-8.64441e-09
0
0
0
-1.01283e-08
-1.03598e-08
-1.09536e-08
0
0
0
-1.29333e-08
-1.32577e-08
-1.40739e-08
0
0
0
-1.67663e-08
-1.71719e-08
-1.82183e-08
0
0
0
-2.11411e-08
-2.13324e-08
-2.19324e-08
-2.29834e-08
0
0
0
-2.50653e-08
-2.49111e-08
-2.52797e-08
-2.61831e-08
0
0
0
0
-2.80991e-08
-2.77534e-08
-2.81132e-08
-2.90127e-08
0
0
0
0
-3.11371e-08
-3.06585e-08
-3.10425e-08
-3.153e-08
-3.25285e-08
0
0
0
0
0
-3.57539e-08
-3.51538e-08
-3.54954e-08
-3.6443e-08
-3.67535e-08
0
0
0
-4.09139e-08
)
;
    }


matejfor May 11, 2010 07:37

sure it does!

value needs scalar or vector, as you set in type inletOutlet BC, which is mainly Dirichlet BC, which wants number. the keyword zeroGradient is setting Neumann type BC with a specified flux =0.
change value to a vector like (0 0 0).

good luck
matej

heavy_user May 18, 2010 09:29

Quote:

Originally Posted by matejfor (Post 258311)
sure it does!

value needs scalar or vector, as you set in type inletOutlet BC, which is mainly Dirichlet BC, which wants number. the keyword zeroGradient is setting Neumann type BC with a specified flux =0.
change value to a vector like (0 0 0).

good luck
matej

Hi matej,

thx for your answer!
It does, in deed. And if you use it correctly the solver wont accept O-Gradient.
I forgot the ; after inletValue () ; :rolleyes:, so he didi not complain about O-gradient.

I am trying to simulate a jetflame. Unfortunately I still have inflow in the area of the cowflow using inletOutlet for a cowflow velocity below 1.5 m/sec. Is this BC generally unstable for very low velocities ???

regards!

Tobi September 6, 2012 08:11

Quote:

Originally Posted by eugene (Post 192168)
For an outlet that sometimes has inflow:

U:outlet
{
type inletOutlet;
inletValue uniform (0 0 0);
value uniform (0 0 0);
}

Note: this does not guarantee the inflow wont become unbounded.

Basically, inletOutlet is zero gradient unless the flow is inward in which case it is fixed value (inletValue). outletInlet is zero gradient if the flow is inward and fixed value (outletValue) if the flow is outward.


Hi,

if I set up inletValue uniform (0 0 0), then I have no inlet flow couse the inlet flux is set to zero. Is that correct?

If there are faces with inlet flow and I set inletValue uniform (0 0 1), then I ll have an flow inside my domain with the velocity vector of (0 0 1).

Is that right ?

So in my case I have an vortex-breakdown after a diffuser. If I am using inletOutlet, then I get just a piece of outlet faces and the rest, where the flow should go back is fixed with (0 0 0).

Should I use "pressureInletOutletVelocity" for that case?
But I set fixed pressure at the outlet :/ ?

Any suggestions
Thanks

Tobi

mturcios777 October 30, 2012 17:44

Question about inletOutlet/outletInlet
 
[THIS SHOULD BE ITS OWN THREAD; I HAD MULTIPLE WINDOWS OPEN AND MADE A MISTAKE. ADMINS, COULD YOU DELETE THIS POST?]

Hello everyone,

I'm looking about implementing a custom boundary condition that simulates a check valve, and I believe I can base it on mixedFvPatchField like the inletOutlet/outletInlet patch.

The user guide (http://www.openfoam.org/docs/user/boundaries.php) mentioned that inletOutlet switched U and p between zeroGradient and fixedValue depending on the direction of the flow, but I have been unable to find out how this is done. From reading the source, it seems that it only switches between zeroGradient and fixedValue depending on the flux. I'd like to know where the switch happens (it may be in mixedFvPatch field, but I can't find it).

I want to know in case I need to make changes there. Or is the the U/p switch a typo/deprecated feature that was never cleaned out of the manual.

Thanks!

KateEisenhower June 8, 2015 03:02

Quote:

Originally Posted by eugene (Post 192168)
For an outlet that sometimes has inflow:

U:outlet
{
type inletOutlet;
inletValue uniform (0 0 0);
value uniform (0 0 0);
}

Note: this does not guarantee the inflow wont become unbounded.

Basically, inletOutlet is zero gradient unless the flow is inward in which case it is fixed value (inletValue). outletInlet is zero gradient if the flow is inward and fixed value (outletValue) if the flow is outward.

Hello,

thank you for the explanation. However, I looked at the simpleFoam/Motorbike tutorial where they defined the inlet and outlet BCs for velocity as follows:

Code:

    inlet
  {
      type            fixedValue;
      value          uniform (20 0 0);
    }

    outlet
    {
        type            inletOutlet;
        inletValue    uniform (0 0 0);
        value          uniform (20 0 0);
    }

Isn't this over-determined than? Wouldn't it be better to set zeroGradient to the outlet?

Thank you in advance,

Kate

Bana December 25, 2015 16:44

Hi everybody
Recently I have tried this boundary condition "inletOutlet" at the outlet patch of my case to prevent back flow but it didn't work and I had reverse flow at the outlet. I have no idea what is wrong?
U:outlet
{
type inletOutlet;
inletValue uniform (0 0 0);
value uniform (0 0 0);
}
The same was set for K,epsilon files too.
Any insight would be very much appreciated.
Thanks in advance


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