ENH: pureZoneMixture: different mixture properties according to cellZone

Summary

Use a different mixture on a per-cell basis.

Details of new models (If applicable)

In the thermoPhysicalProperties one can now select the new pureZoneMixture model. It is a drop-in replacement for pureMixture where the mixture properties itself are sub selected by cellZones. In below example (for a solid mesh) there are two cellZones, heater1 and heater2. The second, heater2 has slightly different properties:

thermoType
{
    type            heSolidThermo;
    mixture         pureZoneMixture;    //pureMixture;
    transport       constIso;
    thermo          hConst;
    equationOfState rhoConst;
    specie          specie;
    energy          sensibleEnthalpy;
}

mixture
{
    heater1
    {
        specie
        {
            molWeight   50;
        }

        transport
        {
            kappa   80;
        }

        thermodynamics
        {
            Hf      0;
            Cp      450;
        }

        equationOfState
        {
            rho     8000;
        }
    }
    heater2
    {
        //- Start off from heater1 properties
        ${heater1}

        //- Selectively overwrite properties
        equationOfState
        {
            rho     4000;
        }
    }
}

Risks

• the input works with the usual explicit boundary conditions (compressible::turbulentTemperatureRadCoupledMixed) for chtMultiRegionFoam. The only difference is that the per-cell properties are looked up through the cellZone the cell is in.
• the two cellZones can also not be separated (i.e. share faces) in which case attention has to be paid to the interpolation scheme (e.g. harmonic)