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-   -   inhomogeneous XiFoam, problems with "ft" phase inlet (https://www.cfd-online.com/Forums/openfoam-solving/98323-inhomogeneous-xifoam-problems-ft-phase-inlet.html)

 roby March 8, 2012 07:10

inhomogeneous XiFoam, problems with "ft" phase inlet

Dear Foamers,

I am simulating the dispersion of a "pollutant" phase in air by using the inhomogeneous mixture of the XiFoam solver (some forums suggest similar approaches). Of course I turned off the reaction.

The case is very simple. I have:
• A flow-field with inlet (velocity) and outlet (pressure)
• An external wall that I declared as a symmetry plane
• A wall body in the field
• Finally a small injection area on the body, where I impose a velocity inlet (zeroGradient pressure) and an "ft" concentration of 1.
Here is the bizarre behavior:
• For the case here above described, the velocity and pressure field solution behave approximately as expected. A vector field coming out of the injection area reflects the velocity magnitude I imposed. Nevertheless, no "ft" phase is observed in all the field BUT at the very entry of the injection boundary condition (jump from 1 to zero in the framework of one cell)
• I once tried and put "ft=1" at the inlet and I let run. Just to see whether I got right the use of the routine. In this second case, not only ft came out of the inlet BC. Even the injection BC started to spit out the second phase.
I first thought I was using an old version of OpenFOAM (1.6.0) and then I installe a brand new one (2.1.0) but still... the same behavior

has anyone encounter similar behaviors? is it just a bug of the software?

 Pier84 June 14, 2016 09:36

ft does not decrease after combustion (b=0)

Hi,

In my case ft does not decrease after that combustion occurs (b-->0).
It diffuses and spreads coherently and also the combustion occurs properly but when b-->0 in a cell ft remains with a nonzero value. I expect that ft decreases during combustion and after it becomes --> 0.

Below are my key settings. Modify for inhomogeneous mixtures: fvSolution, thermophysicalProperties and setting initial condition for ft should be enough... but ft does not go to 0 after combustion.

Thanks,
PO

fvSolution
"(U|b|Su|Xi|ft|ha|hau|k|epsilon)"
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-05;
relTol 0.1;
}

"(U|b|Su|Xi|ft|ha|hau|k|epsilon)Final"
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-05;
relTol 0;

thermophysicalProperties
{
type heheuPsiThermo;
mixture inhomogeneousMixture;
transport sutherland;
thermo janaf;
equationOfState perfectGas;
specie specie;
energy absoluteEnthalpy;
}

stoichiometricAirFuelMassRatio stoichiometricAirFuelMassRatio [0 0 0 0 0 0 0] 34.074;

fuel // Hydrogen H2

oxidant // Air

burntProducts // Water vapor + N2

 Uyan June 29, 2016 07:26

XiFoam : thermophysical properties : inhomogeneous mixture

Hi Pierluigi,

I am trying to use XiFoam for a simulation with two inlets of fuel supplies with same gas but different concentrations. Hope you can help me a little in this situation.

I need to modify the thermophysicalProperties file. However, I can't figure out how to do this for a situation where I have two different equivalence ratios as inlets.

Can you please let me know how did you change the thermophysicalProperties dictionary entries for a new fuel and burntProducts?

 Pier84 July 3, 2016 09:38

RE: XiFoam : thermophysical properties : inhomogeneous mixture

Hi Roby,

You may want to use ft and inhomogeneous mixture instead of ER and homogeneous mixture.
In the thermophysical properties file there is not distinction within two or oo mixtures with different ft thus just setup for one mixture (e.g. the stoichiometric one):

e.g.

fuel // Hydrogen H2
oxidant // Air
burntProducts // Water vapor + N2

Pierluigi

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