flame height comparison with heskestad

[Mardy Owens]

Hi,

I am doing a case study with a 1.5x1.5 burner having a constant heat release rate of 5000 kW. As you have done in the validation guide, I have calculated the flame Height, that in my case is 5.05 m. I have done the same case at 0.25 , 0.125 and 0.0625 m. But I get height of 6 (for the coarser) and 7 for the finer, using the 99% of the HRR.

Do you have suggestions of what can effect these discrepancies?

Thanks in advance

[dr_jfloyd]

Heskestad's correlation is not a real fire. That 5.05 m has some uncertainty associated with it. You should not expect that FDS (or an actual 5000 kW fire with the same burner size) will have the same flame height as the correlation. Additionally, Heskestad's correlation is not based on the idea of achieving a specific fraction of the total heat release. If you look at the FDS Validation guide (Fig. 6.36) you will see that using 99 % for the flame height generally results in larger flame heights than predicted by any of the common correlations, and the use of 95 % generally results in smaller flame heights. Your results are in line with the results shown in that Figure.