Extinction model 2 grid size

[r-broek]

The FDS user guide mentions that a relatively fine grid is required for the EXTINCTION 2 model. I was wondering if there is a way to quantify this, let's say compared to the Kolmogorov scale? For example, I am running a simulation where the Kolmogorov scale is on the order of 0.1 mm and I am using a grid size of 75 mm. In this case, the grid size is 750 times the Kolmogorov scale. Can this be considered relatively fine?

Also, I was wondering if it might be helpful to add the default extinction models of the simulation modes to table 19.1 in the Numerical Considerations chapter in the FDS user guide. When I first read the chapter, I thought the simulation modes changed only the parameters that were listed in that table.

[drjfloyd]

Good comment on Table 19.1. I will add to the table. An oversight on our part.

I don't think we have data to be as specific as some minimum ratio to the Kolmogorov scale or even give some maximum cell size for the use of EXTINCTION 2. At 75 mm you might still be a little large. You could try your case with each mode and see if the EXTINCTION 2 results look reasonable.

[r-broek]

EXTINCTION 1 yielded better results, so I wanted to check if I could justify using it instead of EXTINCTION 2, beyond the fact that it is more accurate. That said, I suppose better results are reason enough. Thanks a lot for your response!