Thunderhead Engineering Forum

Please login or register.

Login with username, password and session length
Advanced search  

News:

Forum moved to https://forum.thunderheadeng.com

Author Topic: Fire spread on facade  (Read 904 times)

hey_youu

  • New Member
  • *
  • Posts: 7
    • View Profile
Fire spread on facade
« on: April 02, 2020, 12:00:58 pm »

Hi everyone!
i am trying to simulate a fire as the video below,
https://www.youtube.com/watch?v=XBtZDF-2Pgc&t=3s

My PyroSim model and result are shown below. I have run the simulation for like 20 hours for a 90 seconds video, yet, the fire does not spread at all. What can i do to make the fire spread like the video and speed up the simulation? Thank you!

result,
https://youtu.be/dLKss9uSiGI
Logged

Dave McGill

  • Member
  • ***
  • Posts: 166
    • View Profile
    • firemodel.ca
Re: Fire spread on facade
« Reply #1 on: April 11, 2020, 02:00:08 pm »

There are a couple of obvious problems.

1. A mesh with 1.1 million cells is way too big. I would sub-divide into 4 meshes.

2. The domain is a sealed box.

If this is your first model, then I suggest you try and get a simple fire burning, without the complicated geometry.

Dave
Logged
Dave McGill
firemodel.ca

hey_youu

  • New Member
  • *
  • Posts: 7
    • View Profile
Re: Fire spread on facade
« Reply #2 on: April 12, 2020, 10:27:13 am »

Thank you for answering! May i know more about the problems.

1. How i should divide the meshes? I should divide it over the whole model evenly or just divide it in the burning area (the vertical channel)?

2. How can i change my domain to the appropriate one? I cannot find it in the manual.

Logged

Dave McGill

  • Member
  • ***
  • Posts: 166
    • View Profile
    • firemodel.ca
Re: Fire spread on facade
« Reply #3 on: April 13, 2020, 11:58:55 am »

1. How i should divide the meshes? I should divide it over the whole model evenly or just divide it in the burning area (the vertical channel)?

I'd start by using the spit-mesh feature to divide into 4 equal meshes (as cube-like as possible).

2. How can i change my domain to the appropriate one? I cannot find it in the manual.

Right-click on the mesh -> Open Mesh Boundaries. then delete the Zmin open vent
Logged
Dave McGill
firemodel.ca

hey_youu

  • New Member
  • *
  • Posts: 7
    • View Profile
Re: Fire spread on facade
« Reply #4 on: April 27, 2020, 10:27:33 am »

Thank you for helping me once again. Yet, the fire still doesn't spread. I have split the the model to 4 meshes, opened the the boundaries and run the simulation up to 2 mins. The result is still similar to the previous one. What can i do?
Logged

Dave McGill

  • Member
  • ***
  • Posts: 166
    • View Profile
    • firemodel.ca
Re: Fire spread on facade
« Reply #5 on: April 28, 2020, 09:26:25 am »

If you attach the Pyrosim file, then I'll have a look.
Logged
Dave McGill
firemodel.ca

hey_youu

  • New Member
  • *
  • Posts: 7
    • View Profile
Re: Fire spread on facade
« Reply #6 on: April 28, 2020, 11:15:30 am »

This is my model, thank you!
Logged

Dave McGill

  • Member
  • ***
  • Posts: 166
    • View Profile
    • firemodel.ca
Re: Fire spread on facade
« Reply #7 on: April 28, 2020, 12:38:58 pm »

Check your source for the heat of combustion of polyethylene. I suspect it was in the units of kJ/g. FDS uses a value of kJ/kg. (So the value should be 1,000x larger.  :-)

I also suggest you add a boundary file for burning rate.
Logged
Dave McGill
firemodel.ca

hey_youu

  • New Member
  • *
  • Posts: 7
    • View Profile
Re: Fire spread on facade
« Reply #8 on: April 29, 2020, 05:07:04 am »

I have adjusted the heat of combustion of polyethylene. Where can i set the burning rate and what value i should put in?
Logged

Dave McGill

  • Member
  • ***
  • Posts: 166
    • View Profile
    • firemodel.ca
Re: Fire spread on facade
« Reply #9 on: April 29, 2020, 07:03:32 am »

A boundary fire for burning rate shows, on a cell by cell basis, the spread of a fire.
Output -> Boundary Quantities -> Burning Rate

I also added a boundary file for Temperature.

The surface of Polyethylene has mass loss rate of 0.02 kg/(m^2 s). I don't know how valid that is, so I changed to a HRRPUA of 1,000 kW/m^2 to ensure that the fire would spread, if ignited.

I ran it for the set time of 60 s, and the polyethylene surface only reached 105 C, which is well below the ignition temperature of 300 C. I suggest you run it for 600 s. If it does ignite within that time frame, you can go back and play with the mass loss rate value.

Logged
Dave McGill
firemodel.ca

hey_youu

  • New Member
  • *
  • Posts: 7
    • View Profile
Re: Fire spread on facade
« Reply #10 on: May 07, 2020, 10:40:51 am »

Hi Dave, how i can find the surface temperature of the wall?
Besides, if i change the heat release rate of the fire to 2500 kW, do you think this is reasonable?
Logged

Dave McGill

  • Member
  • ***
  • Posts: 166
    • View Profile
    • firemodel.ca
Re: Fire spread on facade
« Reply #11 on: May 08, 2020, 07:00:53 pm »

Add a boundary file for wall temperature.
Logged
Dave McGill
firemodel.ca

hey_youu

  • New Member
  • *
  • Posts: 7
    • View Profile
Re: Fire spread on facade
« Reply #12 on: May 15, 2020, 10:06:54 am »

Thank you Dave! With your timely help, i completed my project on time. How i can contact you for my promise?
Logged