how to set the initial temperature and density of a gas mixture in FDS?
Rick
Hi,
I’m simulating a box with the dimension 2mx2mx2m filled with a gas mixture that has a specific density and temperature, also a flammable material is positioned inside box. The objective of this simulation is to understand whether the defined gas mixture with a specific temperature and density will ignite the flammable material.
Problems with the simulation:
1-The initial calculated pressure is 0Pa when I would expect to be 159763Pa (~1.57atm).
2-The initial gas mixture temperature dropped from 192 C to 20 C in one iteration.
|
s |
C |
Pa |
kg/m3 |
|
Time |
TEMPERATURE |
PRESSURE |
RHO |
|
0.000 |
192.28 |
0.00 |
1.19 |
|
0.110 |
22.65 |
96.97 |
1.19 |
|
0.200 |
22.84 |
274.84 |
1.19 |
I’m quite sure that I’m doing something fundamental wrong. Could you please advise me the best way to setup this problem?
Thanks in advance!
Rick
Input deck below:
Fire Dynamics Simulator
Compilation Date : null
Version : 6.0.0 Serial
OpenMP Disabled
SVN Revision No. : 0
&HEAD CHID='P_Test', TITLE='FDS-6.0, SVN $Revision: 0 $'/
&MESH IJK= 20,20,20, XB= 0.0,2.0, 0.0,2.0, 0.0,2.0 /
&TIME T_END=100.0, WALL_INCREMENT=1, DT=0.01 /
&DUMP NFRAMES=1000, DT_HRR= 0.05, DT_SLCF=0.05, DT_BNDF=0.05/
&MISC TMPA=192.28 /
&SPEC ID='NITROGEN' /
&SPEC ID='OXYGEN' /
&SPEC ID='CARBON DIOXIDE' /
&SPEC ID='WATER VAPOR' /
&INIT XB = 0.0,2.0, 0.0,2.0, 0.0,2.0, TEMPERATURE=192.28, DENSITY=1.190,
SPEC_ID(1)='NITROGEN', MASS_FRACTION(1)=0.772894,
SPEC_ID(2)='OXYGEN' , MASS_FRACTION(2)=0.214041,
SPEC_ID(3)='CARBON DIOXIDE', MASS_FRACTION(3)=0.011399,
SPEC_ID(4)='WATER VAPOR', MASS_FRACTION(4)=0.001666 /
&ZONE XB = 0.0,2.0, 0.0,2.0, 0.0,2.0 /
&REAC C=3,H=8,SOOT_YIELD=0.01,FUEL='PROPANE'/
&SURF ID = 'FOAM SLAB'
COLOR = 'TOMATO 3'
MATL_ID = 'FOAM'
THICKNESS = 0.2
BURN_AWAY = .true.
TMP_INNER = 20.0
BACKING = 'EXPOSED' /
&MATL ID = 'FOAM'
FYI = 'Properties completely fabricated'
SPECIFIC_HEAT = 1.0
CONDUCTIVITY = 0.05
DENSITY = 40.0
N_REACTIONS = 1
NU_SPEC = 1.
SPEC_ID = 'PROPANE'
REFERENCE_TEMPERATURE = 1020.
HEAT_OF_REACTION = 1500.
&OBST XB = 0.80,1.20,0.80,1.20,0.40,0.80, SURF_ID='FOAM SLAB' /
&SURF ID = 'Amb' TMP_FRONT = 192.28 /
&VENT MB='XMIN', SURF_ID='Amb' , COLOR = 'WHITE', TRANSPARENCY = 0.5 /
&VENT MB='XMAX', SURF_ID='Amb' , COLOR = 'WHITE', TRANSPARENCY = 0.5 /
&VENT MB='YMIN', SURF_ID='Amb' , COLOR = 'WHITE', TRANSPARENCY = 0.5 /
&VENT MB='YMAX', SURF_ID='Amb' , COLOR = 'WHITE', TRANSPARENCY = 0.5 /
&VENT MB='ZMIN', SURF_ID='Amb' , COLOR = 'WHITE', TRANSPARENCY = 0.5 /
&VENT MB='ZMAX', SURF_ID='Amb' , COLOR = 'WHITE', TRANSPARENCY = 0.5 /
-----------------------------
# Output Quantities
-----------------------------
&DEVC XYZ= 1.0,1.0,1.0, QUANTITY='TEMPERATURE', ID='TEMPERATURE' /
&DEVC XYZ= 1.0,1.0,1.0, QUANTITY='PRESSURE', ID='PRESSURE' /
&DEVC XYZ= 1.0,1.0,1.0, QUANTITY='DENSITY', ID='RHO' /
&SLCF PBY=1.00,QUANTITY='TEMPERATURE' /
&SLCF PBY=1.00,QUANTITY='PRESSURE' /
&SLCF PBY=1.00,QUANTITY='DENSITY' /
&BNDF QUANTITY='WALL TEMPERATURE' /
&TAIL /
dr_jfloyd
The other problem is due to how INIT is implemented and looks like the guidance in the manual could be improved. INIT does not recompute PAMB. Since you have specified both, prior to the first timestep the values are set to the INIT but immediately after the temp is recomputed based on the equation of state which uses density and PAMB. So what you need to do is specify the PAMB on MISC and one of either density or temperature on INIT.