Boundary conditions: inlet and outlet
 

Hello,


Does anyone know where I can find how to use the boundary conditions?
I've looked at the user guide which tells me that a range of BCs are available at src/finiteVolume/fields/fvPatchFields/derived. But I don't know how to use them. I don't understand what goes with what (for example, a specific BC goes with mixed or calculated?).

I'm studying a flow with an inlet (with a definite velocity) and an outlet. I don't know which BC I have to put for these 2 surfaces (inlet and outlet). As there is no gravity in my problem, I guess I should take a BC which fixes the pressure to zero for the outlet, but I don't know which one.

Could anyone help me? thanks a lot in advance.

For the velocity, you can put:
and for the pressure:
These conditions works with laminar regime.

Regards

David

Repeated post

Hey David,

So what happens when you switch to turbulent? Can you keep the same boundary fields??

T

Hi Foamers,

I have the same question : are you sure it works only in a laminar case, one told me to use such conditions in my turbulent case.
If it does not work in a turbulent case, do you know what kind of boudnary conditions would work so ?

Cheers

PS : Finally those conditions did not work in my DNS case, it gives me a field without any variation ... Help ^^

using outlet velocity profile as inlet
 

Hi All,

Does anyone know how to specify (in COMSOL) an inlet velocity profile from a previously solved model's outlet velocity profile?

I've been trying to create a Fourier Series representation of the profile over time, but I am having trouble doing this with a space and time dimension together.

Any help greatly appreciated. Thank you!

To “using outlet velocity profile as inlet”
 

For this, the form provides two ways, one is mapFields, and the other is directMappedPatch. With the former, I mapped the whole field, but not outlet to inlet. Maybe I take a wrong understanding, you can have a try. I mapped the outlet velocity to the inlet using the directMappedPatch boundary. You should change two files:
1. in constant/polyMesh/boundary
inlet
{
type directMappedPatch;
nFaces #;
startFace #;
offset (0 0 1); // offset (0 0 1) is the distance between the inlet and the outlet
sampleMode nearestPatchFace;
samplePatch outlet;
}


2. in 0/U
inlet
{
type directMappedFixedValue;
value (0 0 0);
setAverage true;
average (0 0 2);
}
Then you can check whether you want results.

problem with boundary
 

I also have problems on defining the bounary. For pressure, when using zeroGradient for inlet, everything goes well. After changing zeroGradient to calculated, I get this message:
valueInternalCoeffs cannot be called for a calculatedFvPatchField
on patch inlet of field p in file "/home/flow/OpenFOAM/flow-1.6/run/pipe/tphase/ke/0/p"
You are probably trying to solve for a field with a default boundary condition.

From function calculatedFvPatchField<Type>::valueInternalCoeffs( const tmp<scalarField>&) const
in file fields/fvPatchFields/basic/calculated/calculatedFvPatchField.C at line 145.


can anyone tell us how to use the boundary conditions?
Thanks

beauty