[Starcatcher]

Hi
during the simulation i want to store the outlet water flow.


Therfore i want to make the following entry to the controlDict:


outletflux
{
type surfaceFieldValue;
libs ("libfieldFunctionObjects.so");
writeControl timeStep;
log true;
// Output field values as well
writeFields false;
regionType faceZone;
name outlet;
operation sum;
// Parameter
fields
(
phi*alpha.water
);
}




As you see i tried to get the summation of all cells of the product of phi and alpha. Obviouly this kind of product needs the right syntaxt. can sombidy tell me how to write phi*alpha.water correctly here?


thanks

[Yann]

Hello,

Originally Posted by Starcatcher

can sombidy tell me how to write phi*alpha.water correctly here?

Short answer: you can't. It's not possible to define operation between variables here. You would have to use another function object to create your field, then use surfaceFieldValue to compute the flowrate.

But a simpler way would be to use alpha.water as weightField when summing phi.

surfaceFieldValue_weightField
    {
        type            surfaceFieldValue;
        libs            ("libfieldFunctionObjects.so");
        log             true;
        writeControl    timeStep;
        writeFields     false;
        surfaceFormat   none;
        regionType      patch;
        name            outlet;
        operation       sum;
        weightField     alpha.water;
        fields
        (
            phi
        );
    }

Or this should also work, assuming you are running interFoam, you should have a alphaPhi0.water variable which is already the alpha.water weighted flux:

surfaceFieldValue_weightField
    {
        type            surfaceFieldValue;
        libs            ("libfieldFunctionObjects.so");
        log             true;
        writeControl    timeStep;
        writeFields     false;
        surfaceFormat   none;
        regionType      patch;
        name            outlet;
        operation       sum;
        fields
        (
            alphaPhi0.water
        );
    }

Both should give the same result.

Cheers,
Yann

[Starcatcher]

Hi Yann,
thank you very much. Yes, i use interFoam. the functions worked, however the sum of my outlets in terms of water flow is bigger than at my inlet.
I think it's because the wightening with alpha is not the best way to calculate the water flux.



Would any body have a better idea?
thanks

[Yann]

It should correspond to the water flux.

What case are you simulating ? Did you reach steady state in your simulation ?

Yann

[Starcatcher]

Hi Yann,
now i reached the steady state. Some of the measurements seem to work.
The case is a simple Y-channel with one inlet and two outlets. the inlet water flow in 0.75m³/s


I run 3 outlet measurement strategees:
1.

flow_outlet11
    {
        type            surfaceFieldValue;
        libs            ("libfieldFunctionObjects.so");
        log             true;
        writeControl    writeTime;
        writeFields     false;
        surfaceFormat   none;
        regionType      patch;
        name            outlet1;
        operation       sum;
        weightField     alpha.water;
        fields
        (
            phi
        );
    }

2.

flow_outlet12
    {
        type            surfaceFieldValue;
        libs            ("libfieldFunctionObjects.so");
        log             true;
        writeControl    writeTime;
        writeFields     false;
        surfaceFormat   none;
        regionType      patch;
        name            outlet1;
        operation       sum;
        fields
        (
            alphaPhi0.water
        );
    }

3.

paraview load case->calculator("alpha.water"*U)->temperal integrator (over converged times steps) -> interpolate variables




Results:
1. strategy:

outlet1: 6.7

outlet2: 4.3
No idea what these values mean.



2. strategy:
oulet1: 0.48
outlet2: 0.24
Looks good, the sum is not quite 0.75m³/s, but close





3. strategy
outlet1: 0.516
outlet2: 0.28
The sum is bigger than 0.75m³/s


So strategy 2 is ok, strategy 3 could be improved maybe.
Thank you for you feedback Yann.