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Author Topic: characteristic diameter  (Read 868 times)

Niklas

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characteristic diameter
« on: May 08, 2018, 05:45:32 am »

Hi,

In tutorial 3 (Modeling Fire, Part 3 – Combustion using HRR), D*=0.819452m obtained from formula. but how they got dx=0.16389 m.
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jharbold

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Re: characteristic diameter
« Reply #1 on: May 30, 2018, 08:46:39 am »

The characteristic diameter as discussed in section 6.3.6 of the FDS User Guide is essentially the number of cells across the input fire diameter in the model.  Dividing the two values that you provided (0.819452/0.16389) gives 5.  While I haven't watched this video, it appears that this is their calculation to determine the minimum size of the cells in the model to ensure that their outputs have adequate grid resolution, which appears to have been selected as 5 cells across the fire.
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