[dwarfgang]

Hello everyone, I am a student who is quite new to using OpenFOAM.
I recently installed a custom solver called rhoReactingCentralFoam (based on OpenFOAM v7) in order to simulate one-step global combustion in a supersonic environment (H2-Air reaction).

From setting up the combustionProperties file in the constant folder (in which I chose the diffusion combustion model), the program asked me to input a scalar value for variable "C." After searching up on the internet, this was the most detailed description I could find for the parameter.
"Additional parameter C is used to distribute the heat release rate in time."
Does it mean that I have to specify the reaction's heat release rate after manual calculation?
I was able to find a correlation for the reaction rate, which was found on the thesis at the bottom of https://repository.tudelft.nl/island...8-9eda89bb04e7 (page 64, under diffusion), but still cannot exactly understand what the variable indicates.
It would be great if someone could offer a thorough explanation on what this is.
Thank you in advance!


-Chris

[rocco_Tororolo]

Hi I am doing simulations in reactingFoam and i encountred the same issues.
did you find any answers?

[dwarfgang]

Originally Posted by rocco_Tororolo

Hi I am doing simulations in reactingFoam and i encountred the same issues.
did you find any answers?

Unfortunately no I implemented an arbitrary value of C = 10, but it does not seem to suit supersonic combustion accurately as the concentration of H2 diminishes much slower compared to similar cases.
Will be looking further into this parameter once I am done writing my Undergrad research paper.

[reverseila]

I don't know anything about combustion...

but There are two combustion models (in $FOAM_SRC/combustionModels) that have this C parameter in them, infinitelyFastChemistry and diffusion

According to the source code, C is a private member variable of type scalar which they commented it as "Model constant"

It is read from a dictionary (not sure from where exactly but I could only find C in infinitelyFastChemistryCoeffs inside combustionProperties files of the $FOAM_TUTORIALS/combustion.)

In the source code of the above combustion models, we have something like these

// file: infinitelyFastChemistry.C
// Constructor definition

template<class ReactionThermo, class ThermoType>
void infinitelyFastChemistry<ReactionThermo, ThermoType>::correct()
{
    this->wFuel_ == dimensionedScalar(dimMass/dimVolume/dimTime, Zero);

    if (this->active())
    {
        this->singleMixturePtr_->fresCorrect();

        const label fuelI = this->singleMixturePtr_->fuelIndex();

        const volScalarField& YFuel =
            this->thermo().composition().Y()[fuelI];

        const dimensionedScalar s = this->singleMixturePtr_->s();

        if (this->thermo().composition().contains("O2"))
        {
            const volScalarField& YO2 = this->thermo().composition().Y("O2");

             // wFuel: Fuel consumption rate
            this->wFuel_ ==
                this->rho()/(this->mesh().time().deltaT()*C_)
               *min(YFuel, YO2/s.value());
        }
    }
}
...

// file: diffusion.C
...
// Constructor definition
template<class ReactionThermo, class ThermoType>
void diffusion<ReactionThermo, ThermoType>::correct()
{
    this->wFuel_ == dimensionedScalar(dimMass/dimVolume/dimTime, Zero);

    if (this->active())
    {
        this->singleMixturePtr_->fresCorrect();

        const label fuelI = this->singleMixturePtr_->fuelIndex();

        const volScalarField& YFuel =
            this->thermo().composition().Y()[fuelI];

        if (this->thermo().composition().contains(oxidantName_))
        {
            const volScalarField& YO2 =
                this->thermo().composition().Y(oxidantName_);

            this->wFuel_ ==
                C_*this->turbulence().muEff()
               *mag(fvc::grad(YFuel) & fvc::grad(YO2))
               *pos0(YFuel)*pos0(YO2);
        }
    }
}
...

Hope this helps!