# LTSInterFoam BC problem

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June 16, 2015, 10:38
LTSInterFoam BC problem
#1
New Member

xu cong
Join Date: Jun 2015
Posts: 4
Rep Power: 3
Hello Foamers
I am new to Openfoam and I am doing a simulation about drainage,you can see model I use from the attachment

length=5.5m
width=3m
depth=0.1m

The left side is inlet (Q=20 L/s)
The right side is outlet and there is a gully on the bottom.(we can assume the gully is the second outlet)
The top floor is atmosphere.

I used the LTSInterFoam for simulation because I heard this Foam is faster than interFoam.However, I found some very strange result after simulation:

1.As you can see in the attachment, the water cannot get into the gully.
2.The flow rate of inlet is not equal to the flow rate of two outlets.

I think it should be the problem of boundary condition, but I don't know which one it is.
So I listed my files U/P_pgh/alpha, I hope someone could help me.

P_pgh
Code:
```dimensions      [1 -1 -2 0 0 0 0];

internalField   uniform 0;

boundaryField
{
inlet
{
type           buoyantPressure;
value          uniform 0;

}

outlet
{
}

outlet2
{
}

sides
{
type           buoyantPressure;
value          uniform 0;
}

atmosphere
{
type           totalPressure;
p0              uniform 0;
U               U;
phi             phi;
rho             rho;
psi             none;
gamma           1;
value           uniform 0;
}

lowerwall
{
type            buoyantPressure;
value          uniform 0;
}
}```
U
Code:
```dimensions      [0 1 -1 0 0 0 0];

internalField   uniform (0 0 0);

boundaryField
{
inlet
{
type            flowRateInletVelocity;
volumetricFlowRate  constant 20e-3;
rhoInlet            1000;
}

outlet
{
}

outlet2
{
}

sides
{
type            fixedValue;
value           uniform (0 0 0);
}

atmosphere
{
type            pressureInletOutletVelocity;
value           uniform (0 0 0);
}

lowerwall
{
type            fixedValue;
value           uniform (0 0 0);
}
}```
alpha
Code:
```dimensions      [0 0 0 0 0 0 0];

internalField   uniform 0;

boundaryField
{
inlet
{
type            inletOutlet;
inletValue     uniform 1;
value           uniform 1;
}

outlet
{
}

sides
{
}

atmosphere
{
type            inletOutlet;
inletValue     uniform 0;
value           uniform 0;
}

lowerwall
{
}

outlet2
{
}
}```
Lastly,can anyone tell me how to calculate the flow rate of water in this multiphase flow.I used the 'calculator' and 'integrate variable' from paraview.However i don't think it is precise.
Any help would be great, thank you so much!
Attached Images
 model.jpg (8.7 KB, 28 views) gully problem.jpg (14.7 KB, 27 views)

 June 24, 2015, 09:02 #2 Senior Member     Tobias Holzmann Join Date: Oct 2010 Location: Leoben (Austria) Posts: 1,555 Blog Entries: 6 Rep Power: 27 Hi, Boundary Condition for U for the outlet you can use inletOutlet and set inletValue to zero to provide no backflow the rest is okay Boundary Condition for alpha all boundary conditions are okay. Due to U you can set different BC for alpha. here for example you can use zeroGradient for outlets, if you have determined that there is no backflow Boundary Condition for p_rgh the old game (: p_rgh is some imaginary pressure maybe my small description will help you (it's not 100% correct, too lazy to make a new one ) Code: ```inlet :: fixedFluxPressure all walls :: fixedFluxPressure outlet :: zeroGradient atmosphere :: depend what you want, I always prefer to set the prghPressureBC``` sharonyue likes this. __________________ Best regards, Tobias Holzmann Some interesting OpenFOAM tutorials, publications and videos on www.Holzmann-cfd.de OpenFOAM Beginners should check out the new wiki on wiki.openfoam.com A list of some active OpenFOAM contributers can be found »here« A book about the basics of »Mathematics, Numerics, Derivations and OpenFOAM« can be found on www.Holzmann-cfd.de

 June 26, 2015, 04:20 #3 New Member   xu cong Join Date: Jun 2015 Posts: 4 Rep Power: 3 Thank you so much for your kind reply, my model seems better now, but there is still a problem about the velocity in the vertical exit. The exit is just some fast air flow, the velocity is more than 1000m/s which is obviously wrong, and the pressure is very low.

June 26, 2015, 04:35
velocity problem
#4
New Member

xu cong
Join Date: Jun 2015
Posts: 4
Rep Power: 3
The simulation is better
but there is a problem with the vertical exit
The air speed is super high with a low pressure.

Why is that? is it because of the pressure of atmosphere?
Attached Images
 vitesse problem.png (18.2 KB, 17 views) vitesse problem2.png (30.3 KB, 18 views)

 June 29, 2015, 07:48 #5 Senior Member     Tobias Holzmann Join Date: Oct 2010 Location: Leoben (Austria) Posts: 1,555 Blog Entries: 6 Rep Power: 27 Hi, normally you should not ask "why this happens" (: Check your results, and then think about it. For me it seems that you choose a BC configuration that allows you to create a pressure gradient. This gradient will not be compensated with flux, so that a small gradient will always accelerate your flow till infinity or till your solver blow up. Can you share you case? __________________ Best regards, Tobias Holzmann Some interesting OpenFOAM tutorials, publications and videos on www.Holzmann-cfd.de OpenFOAM Beginners should check out the new wiki on wiki.openfoam.com A list of some active OpenFOAM contributers can be found »here« A book about the basics of »Mathematics, Numerics, Derivations and OpenFOAM« can be found on www.Holzmann-cfd.de

June 29, 2015, 08:51
case
#6
New Member

xu cong
Join Date: Jun 2015
Posts: 4
Rep Power: 3
Here is my case.
It has been over two weeks and I can't solve it so I was a little bit frustrated, sorry about that.
Attached Files
 case.zip (24.2 KB, 5 views)

 Tags boundary condition, flow rate, multiphase flow

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