Thunderhead Engineering Forum

Public Forum => PyroSim => Topic started by: hey_youu on April 02, 2020, 12:00:58 pm

Title: Fire spread on facade
Post by: hey_youu 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 (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 (https://youtu.be/dLKss9uSiGI)
Title: Re: Fire spread on facade
Post by: Dave McGill 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
Title: Re: Fire spread on facade
Post by: hey_youu 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.

Title: Re: Fire spread on facade
Post by: Dave McGill 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
Title: Re: Fire spread on facade
Post by: hey_youu 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?
Title: Re: Fire spread on facade
Post by: Dave McGill on April 28, 2020, 09:26:25 am
If you attach the Pyrosim file, then I'll have a look.
Title: Re: Fire spread on facade
Post by: hey_youu on April 28, 2020, 11:15:30 am
This is my model, thank you!
Title: Re: Fire spread on facade
Post by: Dave McGill 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.
Title: Re: Fire spread on facade
Post by: hey_youu 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?
Title: Re: Fire spread on facade
Post by: Dave McGill 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.

Title: Re: Fire spread on facade
Post by: hey_youu 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?
Title: Re: Fire spread on facade
Post by: Dave McGill on May 08, 2020, 07:00:53 pm
Add a boundary file for wall temperature.
Title: Re: Fire spread on facade
Post by: hey_youu 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?