Custom Smoke

[Vishwanath M.G]

Hey everyone, 

Hope everyone's doing well. I would like to know about the custom smoke feature that is available in FDS. I am new to the software and it would be great if someone explains it. Also,  I tried to find information regarding this, but couldn't find much. Kindly do the needful as soon as possible

[dr_jfloyd]

What do you mean by custom smoke feature?

Have you read the FDS Technical Reference Guide and User's Guide?

[Vishwanath M.G]

Yes! I mean can you tell me how to define a smoke with some particular temperature and inject it into the domain using a vent? Because I am working pyrosim software and I am unable to find how to do it in the pyrosim but I think we can directly write an FDS code right?  

[dr_jfloyd]

Yes you can directly write FDS code.  Please consult the FDS User's Guide. Very example in the guide is provided to you in an Examples folder where you installed FDS.

[Vishwanath M.G]

Thank you for the reply. I had gone through that example folder already but the issue was I was unable to visualize the soot in the postprocessing. So the description of the work is just to emit the soot from the vent without any reaction. I have attached the code below kindly help me out.

[D D]

You will not see any smoke production if all you do is injecting species, that is, without REAC line. If you want to visualize soot, make a 3D slice.

In Pyrosim, use typically use a SUPPLY type surface for just injecting species.

[dr_jfloyd]

D D is partially correct. The smoke3D files are created when there is a reaction. Without a reaction you can still get those files, howeve, you willl need to tell FDS to write the files  -- see 18.3.5 in the User's Guide.

However, you have other problems:

-HRRPUA is not an appropriate input if you just want to inject smoke without a reaction. HRRPUA tells FDS to inject the FUEL from the REAC line. 

-VEL=0.  You have told FDS that there is nothing being injected at this surface. If you don't add any smoke, you aren't going to see any smoke.

&SURF ID='Smoke',
      COLOR='RED',
      VEL=0.0,
      TMP_FRONT=300.0,
      MASS_FRACTION(1)=1.0E-4,
      SPEC_ID(1)='SOOT',
      TAU_MF=1.0,
      HRRPUA=0.0/

[D D]

The SUPPLY type surface in PYROSIM eliminates the VEL automatically as long the "Specify Mass Flux of Individual Species" is clicked. Also the HRRPUA parameter makes no sense so it is also eliminated. I am talking totally Pyrosimwise.

[Vishwanath M.G]

Thank you for the reply. So the issue here is I do not know the value of mass flux of soot to use the "Specify Mass Flux of Individual Species" this feature, but the mass fraction is known. Is there a way to determine mass flux through mass fraction?

[D D]

I think there is an option to define yields too. If you do not write FDS code directly, this option may be available in the 'LAYERED' SURF type. 

Alternatively, if you know the total MLR and the soot yield, then you are only one multiplication away.

[Dave Sheppard]

If you want to visualize the obscuration of the smoke without a reaction an option would be to inject the smoke as a species and then specify the species on a &DUMP line.  Look for SMOKE3D in the user's guide.

[Dave Sheppard]

Oops. I was looking at an old input file.  Add smoke3D with a SM3D name list.

[Vishwanath M.G]

Thank you so much for the reply Dave, will figure out how to implement it.

[Dan]

Hi all,

I want to simulate the gas species in the event of fire. I used SUPPLY surface and input the Mass Flux for gas species and NET HEAT FLUX for Thermal Boundary Conditions. Here are my problems:

1. I saw in other posts that REAC is not required if HRRPUA is not used. But I tried it in my own model and FDS required REAC when I used SUPPLY surface. 
2. I have put a few gas devices at different heights to measure the gas species, the current result shows that gas only concentrates near the SUPPLY surface. I expect to see the higher gas concentration at higher elevations due to the buoyancy.

I just show part of the ramp up values of the gas species and NET HEAT FLUX below. 

Thank you.

&SPEC ID='SULFUR DIOXIDE', FORMULA='SO2'/
&SPEC ID='NITROGEN', FORMULA='N2'/
&SPEC ID='CARBON MONOXIDE'/
&SPEC ID='HYDROGEN FLUORIDE', FORMULA='HF'/
&SPEC ID='HYDROGEN CHLORIDE', FORMULA='HCl'/
&SPEC ID='HYDROGEN CYANIDE', FORMULA='HCN'/
&SPEC ID='NITRIC OXIDE', FORMULA='NO'/
&SPEC ID='POLYURETHANE', FORMULA='C25H42O6N2', CONDUCTIVITY=0.0215, SPECIFIC_HEAT=1.4/

&REAC ID='Reaction4',
      FUEL='POLYURETHANE',
      SOOT_YIELD=0.064,
      HEAT_OF_COMBUSTION=2.1E+4/

&SURF ID='BEV',
      RGB=255,102,153,
      NET_HEAT_FLUX=1666.67,
      RAMP_Q='BEV_RAMP_Q',
      MASS_FLUX=2.0E-3,6.67E-4,6.2E-5,3.0E-4,2.29E-4,3.22E-4,
      SPEC_ID='CARBON MONOXIDE','HYDROGEN CHLORIDE','HYDROGEN CYANIDE','HYDROGEN FLUORIDE','NITRIC OXIDE','SULFUR DIOXIDE',
      RAMP_MF='BEV_RAMP_MF','BEV_RAMP_MF-2','BEV_RAMP_MF-3','BEV_RAMP_MF-4','BEV_RAMP_MF-5','BEV_RAMP_MF-6'/

&RAMP ID='BEV_RAMP_MF', T=0.0, F=0.0/
&RAMP ID='BEV_RAMP_MF', T=131.155616, F=0.0/
&RAMP ID='BEV_RAMP_MF', T=231.637348, F=0.0/
&RAMP ID='BEV_RAMP_MF', T=309.151827, F=0.0/
&RAMP ID='BEV_RAMP_MF', T=389.537212, F=1.582904E-3/
&RAMP ID='BEV_RAMP_MF', T=469.683356, F=4.24321E-3/
&RAMP ID='BEV_RAMP_MF', T=543.020298, F=0.022963/
&RAMP ID='BEV_RAMP_MF', T=581.272762, F=0.046453/
&RAMP ID='BEV_RAMP_MF', T=594.08931, F=0.073343/
&RAMP ID='BEV_RAMP_MF', T=620.866035, F=0.159339/

...

&RAMP ID='BEV_RAMP_MF-2', T=0.0, F=0.0/
&RAMP ID='BEV_RAMP_MF-2', T=145.021075, F=9.787772E-3/
&RAMP ID='BEV_RAMP_MF-2', T=249.341412, F=6.298125E-3/
&RAMP ID='BEV_RAMP_MF-2', T=340.621707, F=0.011631/
&RAMP ID='BEV_RAMP_MF-2', T=492.755532, F=5.382317E-3/
&RAMP ID='BEV_RAMP_MF-2', T=590.866326, F=5.874852E-3/
&RAMP ID='BEV_RAMP_MF-2', T=654.452055, F=0.024115/
&RAMP ID='BEV_RAMP_MF-2', T=672.418335, F=0.067729/
&RAMP ID='BEV_RAMP_MF-2', T=692.702845, F=0.111448/
&RAMP ID='BEV_RAMP_MF-2', T=750.948367, F=0.144528/
&RAMP ID='BEV_RAMP_MF-2', T=766.596417, F=0.166493/

...

&RAMP ID='BEV_RAMP_MF-3', T=0.0, F=0.0/
&RAMP ID='BEV_RAMP_MF-3', T=324.507887, F=0.044944/
&RAMP ID='BEV_RAMP_MF-3', T=356.534334, F=0.07572/
&RAMP ID='BEV_RAMP_MF-3', T=357.633281, F=0.168743/
&RAMP ID='BEV_RAMP_MF-3', T=410.805394, F=0.027613/
&RAMP ID='BEV_RAMP_MF-3', T=459.560587, F=0.07538/
&RAMP ID='BEV_RAMP_MF-3', T=584.382617, F=0.015473/
&RAMP ID='BEV_RAMP_MF-3', T=586.371187, F=0.078058/
&RAMP ID='BEV_RAMP_MF-3', T=646.656264, F=0.230858/
&RAMP ID='BEV_RAMP_MF-3', T=720.201159, F=0.215009/
&RAMP ID='BEV_RAMP_MF-3', T=745.561467, F=0.268734/
&RAMP ID='BEV_RAMP_MF-3', T=793.746053, F=0.182844/

...

&RAMP ID='BEV_RAMP_MF-4', T=0.0, F=0.0/
&RAMP ID='BEV_RAMP_MF-4', T=135.600698, F=0.0155/
&RAMP ID='BEV_RAMP_MF-4', T=160.766268, F=3.691881E-3/
&RAMP ID='BEV_RAMP_MF-4', T=256.760021, F=5.436418E-3/
&RAMP ID='BEV_RAMP_MF-4', T=351.053097, F=9.768683E-3/
&RAMP ID='BEV_RAMP_MF-4', T=452.526809, F=0.01509/
&RAMP ID='BEV_RAMP_MF-4', T=548.520562, F=0.011019/
&RAMP ID='BEV_RAMP_MF-4', T=656.910359, F=0.01695/
&RAMP ID='BEV_RAMP_MF-4', T=750.55016, F=0.010005/
&RAMP ID='BEV_RAMP_MF-4', T=859.622133, F=8.686044E-3/
&RAMP ID='BEV_RAMP_MF-4', T=921.589648, F=0.109793/
&RAMP ID='BEV_RAMP_MF-4', T=959.555232, F=1.0/

...

&RAMP ID='BEV_RAMP_MF-5', T=0.0, F=0.0/
&RAMP ID='BEV_RAMP_MF-5', T=134.331795, F=3.035867E-3/
&RAMP ID='BEV_RAMP_MF-5', T=237.920549, F=1.089294E-3/
&RAMP ID='BEV_RAMP_MF-5', T=314.719109, F=1.747164E-3/
&RAMP ID='BEV_RAMP_MF-5', T=343.493763, F=0.024845/
&RAMP ID='BEV_RAMP_MF-5', T=398.66172, F=1.506417E-3/
&RAMP ID='BEV_RAMP_MF-5', T=427.237928, F=0.03218/
&RAMP ID='BEV_RAMP_MF-5', T=475.579347, F=1.053247E-3/
&RAMP ID='BEV_RAMP_MF-5', T=553.279418, F=2.412758E-3/
&RAMP ID='BEV_RAMP_MF-5', T=633.099428, F=3.035867E-3/
&RAMP ID='BEV_RAMP_MF-5', T=685.316808, F=0.033593/
&RAMP ID='BEV_RAMP_MF-5', T=689.016407, F=-2.232239E-3/
&RAMP ID='BEV_RAMP_MF-5', T=741.576218, F=0.072031/

...

&RAMP ID='BEV_RAMP_Q', T=0.0, F=0.0/
&RAMP ID='BEV_RAMP_Q', T=42.239962, F=3.227969E-3/
&RAMP ID='BEV_RAMP_Q', T=141.408398, F=2.521907E-3/
&RAMP ID='BEV_RAMP_Q', T=258.261873, F=3.757515E-3/
&RAMP ID='BEV_RAMP_Q', T=365.088316, F=5.383316E-3/
&RAMP ID='BEV_RAMP_Q', T=489.654891, F=7.854533E-3/
&RAMP ID='BEV_RAMP_Q', T=587.00524, F=0.025971/
&RAMP ID='BEV_RAMP_Q', T=630.639352, F=0.070133/
&RAMP ID='BEV_RAMP_Q', T=656.026471, F=0.114607/
&RAMP ID='BEV_RAMP_Q', T=694.437713, F=0.157389/

...

&RAMP ID='BEV_RAMP_MF-6', T=0.0, F=0.0/
&RAMP ID='BEV_RAMP_MF-6', T=152.122843, F=0.335142/
&RAMP ID='BEV_RAMP_MF-6', T=205.239557, F=0.410939/
&RAMP ID='BEV_RAMP_MF-6', T=223.036511, F=0.36425/
&RAMP ID='BEV_RAMP_MF-6', T=252.746333, F=0.327099/
&RAMP ID='BEV_RAMP_MF-6', T=260.222018, F=0.206472/
&RAMP ID='BEV_RAMP_MF-6', T=287.546299, F=0.164883/
&RAMP ID='BEV_RAMP_MF-6', T=323.162468, F=0.386068/
&RAMP ID='BEV_RAMP_MF-6', T=334.474649, F=0.334039/
&RAMP ID='BEV_RAMP_MF-6', T=349.413493, F=0.257869/
&RAMP ID='BEV_RAMP_MF-6', T=356.234625, F=0.21377/
&RAMP ID='BEV_RAMP_MF-6', T=368.016582, F=0.52004/
&RAMP ID='BEV_RAMP_MF-6', T=399.366231, F=0.188077/
&RAMP ID='BEV_RAMP_MF-6', T=439.328421, F=0.361904/

...

[dr_jfloyd]

We would need a complete input file to diagnose your problems. 

[dr_jfloyd]

Why do you have this line?

WALL_INCREMENT=10

You have this input:

&SLCF QUANTITY='VISIBILITY', ID='Slice01', PBX=5.0/

VISIBLITY requires SOOT to be present.  If I remove you REAC input, the exact error message given by FDS is:

ERROR: SPEC_ID SOOT is not explicitly specified for QUANTITY VISIBILITY (CHID: Sample_ver4)

You do not have SOOT defined on SPEC. Defining a REAC stops the error since a simple chemistry reaction defines the primitive species of SOOT so it is available fur use if a SOOT_YIELD is given.  However VISIBILITY is never going to change as you have no SOOT being generated by your inputs.

This line says that the surface temperature should be set such that the sum of the radiative and convective flux is 1666.67 kW/m2. Assuming a typical natural convection heat transfer cofficient of ~10 W/m2/K, this would take a surface temperature of ~2100 C and under 1 % of that heat flux will be convective. Is that what you want? This looks like a battery gas source term and most of the energy input would be convective. 

NET_HEAT_FLUX=1666.67

Your mass source is from 4.5 to 5.5 in x and y and you have two boundaries of your domain fully open. No layer is going to form. Your DEVC for HF are not over the mass source. The closest ones are at 5,6.5,1.5 which is a meter away from the edge of the mass source and likely sits outside the plume.

&OBST ID='Fire', XB=4.5,5.5,4.5,5.5,0,1.0, SURF_IDS='BEV','INERT','INERT'/

On Tuesday, August 29, 2023 at 7:29:01 AM UTC-4 Dan wrote:

Here is the input file.

Thank you.

[Dan]

Dear Dr. jfloyd,

Thank you for answering my questions.

I have unchecked the WALL_INCREMENT=10 in the default setting.

Can I know where to input the soot yield other than in REAC? Is it in SOOT Additional Fields (SPEC), or in the Species Injection in SUPPLY surface?

I intend to input the 1666KW/m2 for HRRPUA. Can I input the same value for NET HEAT FLUX if I use SUPPLY surface?

Thank you.

[dr_jfloyd]

If you want SOOT in your domain you can either have a SOOT_YIELD on a REAC and have combustion in the gas phase so that fuel is consumed in the gas, or you can specify a SURF that injects SOOT. If you are using Pyrosim, consult the Pyrosim users guide and the various Pyrosim tutorials for instruction on how to use Pyrosim. If you are stil learning to use FDS and/or Pyrosim, a good approach is to not immeadiately jump to the big complex problem you want to solve. Instead start with simple test problems that run quickly where you test possible approaches to inputs. In this case you could run a simple case of a small domain, with not many grid cells so it runs fast, where you have a supply surface with SOOT being specified and what happens. 

HRRPUA is a mass flux boundary condition.  NET HEAT FLUX Is a temperature boundary condition. With HRRPUA the energy isn't realized until the fuel mixes with air and burns, i.e., the energy release will occur over a volume in space. With NET HEAT FLUX, FDS will set the temperature so the sum of the radiative and convective fluxes equals NET HEAT FLUX. Which one is appropriate for you specific needs is a decision you need to make and justify as the modeler.