[TurbuGuu]

Dear friends,

I am using OpenFOAM 8 to conduct a large eddy simulation of a premixed flame. Combined with the PaSR combustion model, I have obtained preliminary calculation results. Now I would like to get the Damköhler Number field. When using the PaSR model, we can get kappa. From the mathematical expression, it seems that the Damköhler Number can be directly equal to (1/kappa)-1.

What I am confused about is whether the parameters such as muEff and epsilon used in calculating kappa in the PaSR model are at the sgs level? If it is at the sgs level, why does the PaSR model only use the parameters of the sgs scale for calculation instead of the parameters of the (sgs+ resolved)? Are they consistent with the parameters such as muEff and epsilon that I directly obtained through the OpenFOAM post-processing function. If they are not only at sgs level, is it correct to directly use (1/kappa)-1 to calculate the Damköhler number field?

I am new to CFD, any suggestions are welcome. Thank you.

[dlahaye]

My humble suggestion is to seperate non-openfoam-specific and openfoam-specific issues.

1/ non-openfoam-specific
To plot quantities such as Damkolher number field, we have found instances in which computing (using the definition such as e.g Da = t_{turb}/t_{chem}) and plotting fields in Paraview is easier than to extract the Damkohler number field from OpenFoam. E.g., when using the RANS k-eps model, t_turb = k/epsilon. It thus suffices to divide the fields in Paraview. This requires getting acquainted with Paraview.

2/ openfoam-specific
What do you mean at "sgs+resolved" scale?

[TurbuGuu]

Originally Posted by dlahaye

My humble suggestion is to seperate non-openfoam-specific and openfoam-specific issues.

1/ non-openfoam-specific
To plot quantities such as Damkolher number field, we have found instances in which computing (using the definition such as e.g Da = t_{turb}/t_{chem}) and plotting fields in Paraview is easier than to extract the Damkohler number field from OpenFoam. E.g., when using the RANS k-eps model, t_turb = k/epsilon. It thus suffices to divide the fields in Paraview. This requires getting acquainted with Paraview.

2/ openfoam-specific
What do you mean at "sgs+resolved" scale?

Thank you for your reply and suggestions. In RANS simulations, it is indeed possible to calculate the Damköhler number field through parameters such as turbulent kinetic energy and dissipation rate obtained through modeling.

But for LES, most of the turbulent kinetic energy is directly resolved (probably 80%? If my mesh or other settings are good enough), and the rest is described by the sgs model. As for reactive flow, I do not know if the combustion model is only modeled for the sgs level. I recently read some related literature, and some literature mentioned that the parameters in the PaSR model are only for the sgs level. So if this is the case, is the chemical reaction flow in the resolved part still related to the PaSR model? Or does it mean that the analysis part does not require a combustion model?

If PaSR is only for sgs, then although the Damköhler number field can be obtained relatively easily from the PaSR definition (some literature also mentioned that the chemical time scale in the Damköhler number can be automatically calculated by the PaSR model), here only Counted as Da(sgs), it seems that it cannot be regarded as Da(global)?

Not sure if you get what I mean, but thanks again for your reply and advice.

[dlahaye]

Not sure. Should consult literature myself.