Implementing HRRPUA for a (spatially) growing fire

[joelkohyh]

Hi there,

I have experimental HRR data that I wish to simulate in FDS, and I understand the method is to input a HRRPUA into &SURF and then use time-dependent functions (RAMP, TAU) to model the growth/decay. How do I account for the fact that the fire area will grow over time, and hence the fixed input of HRRPUA changes as well?

Thank you.

[mcgratta]

Search the User's Guide for SPREAD_RATE.

[joelkohyh]

Thanks Kevin!

[joelkohyh]

Good day!

I have managed to solve my previous confusion over a higher-than-expected HRR, which was due to not specifying the INERT surfaces on the side and bottom of my fire &OBST. I have also decided to not specify a SPREAD_RATE and instead let the fire "choose its own path via the ignition of heated solid fuels". However, after running the simulation for T_END = 100 and having combustible materials (gypsum walls and wood furniture) near the fire, the output HRR is still largely hovering around 100kW, implying that the fire did not spread.

I have read Chapter 9.2.1 Reaction Mechanism of the FDS User Guide and believe that my error is because I did not specify HEAT_OF_REACTION, HEAT_OF_COMBUSTION, IGNITION_TEMPERATURE etc. With my current code, the material is heating up but not pyrolyzing.

Greatly appreciate any advice you can provide, thank you.
kitchen_100_07.txt

[drjfloyd]

You have no inputs that would support FDS predicting a spreading fire. FDS does not know that pine should burn unless you define this in the input file.

[joelkohyh]

Thank you, are you referring to the addition of N_REACTIONS under &MATL?

[drjfloyd]

There are multiple approaches to defining solid obsrructions tha ignite and burns. N_REACTIONS is one approach. Please carefully read Chapter 9 and study the example files (all of which are provide to you in the Examples folder where FDS is installed on your computer).