Pyrosim - hydrogen Gas release

[Gokul-dev823]

Dear community,

I'm currently learning and simulating a scenario in FDS using Pyrosim and I'm really stuck in a particular area where I would like some suggestions to move forward. I'm trying to simulate a hydrogen gas release from the stove in the kitchen at a release velocity of 97 m/s by creating an obstruction over the stove and defining the surface. I'm getting results which 'm not expecting and that is the fire seems to be very large in the output with more than 2m and spreading over the ceiling. other Sources and validations says that the fire at this velocity cannot be more than 24cm. I have attahced the code file and would be happy to receive any comments suggestions for me to proceed further. I would also like to know where I'm getting it wrong in the code and how to exactly measure the flame height. Thanks
Kitchen_Sim.txt

[mcgratta]

You should not use MASS_FRACTION and VEL on the SURF line. FDS is applying these to your THICKENED obstruction and producing far more mass. Use MASS_FLUX and apply to an area comparable to a grid cell. This will produce an equivalent mass flow.

[Gokul-dev823]

Thanks for your reply. I will run the simulation now and let you know how I am getting on.

[Gokul-dev823]

Im trying to simulate the real case here, so for it I have calculated the velocity of 97.7m/s considering real case of 4mbar pressure from the burner. Now, For the calculated mass flux of 8.8kg/m2s considering the above and assigned it to the obstruction, I could able to see any flame from the output. I ran the simulation for about 60secs. However i defined it under "general surface" and not as a supply.

&SURF ID='Surface02',
COLOR='RED',
MASS_FLUX_TOTAL=8.8,
TMP_FRONT=0.0,
MLRPUA=0.0/

[drjfloyd]

&SURF ID='Surface02',
COLOR='RED',
MASS_FLUX_TOTAL=8.8,
TMP_FRONT=0.0,
MLRPUA=0.0/

Where have you told FDS that your mass flux is hydrogen?

[drjfloyd]

From 10.1.2:

Note that MASS_FLUX_TOTAL should only be used for an outflow boundary condition; for inflow use MASS_FLUX which is discussed in Sec. 10.1.6.

[Gokul-dev823]

yes i just got an understanding over in it and I get what you mean. now even with specifying hydrogen with mass flux of 8.8, I still get the same result except there is increase in velocity in the release region which I understood from slice. and below is the code I have used.

&SURF ID='Surface02',
TMP_FRONT=0.0,
MASS_FLUX=8.8,
SPEC_ID='HYDROGEN',
TAU_MF=1.0/
I'm trying to analyze why I'm not able to visualize fire, and I'm sure at these conditions with vents, fuel and the rate the fire should happen. When i try with defining the specific velocity of 94.7m/s the fire is huge or else no fire with either volume flow rate or mass flux at this rate.

[drjfloyd]

Did you carefully read the MASS_FLUX section of the Guide?

The mass fraction of the background species will be set to account for any mass fraction not specified with other species.

What mass fraction of hydrogen did you specify?

[Gokul-dev823]

i have specified earlier in the code and as 1 like this
&SPEC ID='HYDROGEN', MASS_FRACTION_0=1.0/

[drjfloyd]

Please carefully read the User's Guide description of what MASS_FRACTION_0 on &SPEC does. You need to take the time to make sure you understand what the various FDS inputs mean.