Getting Started with BlenderFDS | Karman Vortex Street

[@firesimandcoding]

More on BlenderFDS: kzbin.info/www/bejne/nJeqi3-BZcSrq5Y

[@Toni_N]

Hey this video is just great. Thank you a thousand times :)

[@firesimandcoding]

Thanks, nice to know that it is helpful! If you have specific questions to BlenderFDS, please feel free to ask.

[@RAyLV17]

Very detailed and helpful video, thank you! Subbed

[@firesimandcoding]

You're welcome, hope it helps!

[@kartiniganesha6741]

Your videos are amazing, very helpful and bring fresh Vibes of incorporated tools with FDS, when I read the user guide. One limitation of GEOM is that it cannot perform heat transfer. So mostly people use the GEOM as a burner. My question, can we use a multiple GEOM in one simulation? Let's say if we want to simulate an entire building with a lot of slender body and curve along with it

[@firesimandcoding]

Hi @kartiniganesha6741 To the best of my knowledge, one can use multiple GEOMs within a single simulation setup. I've done so myself in an earlier version (FDS 6.7.7). There I used a GEOM to determine the radiative heat flux to the sample in a cone calorimeter. Said model consists of three GEOMs: top and bottom plate as well as the heating element, see video here on the channel: kzbin.info/www/bejne/Z3i8kJqdrJashqM. Please also have a look at the FDS users guide of the nightly builds: github.com/firemodels/test_bundles/releases/tag/FDS_TEST There is some discussion on limitations of the GEOMs presented. For example thin GEOM cannot divide a fluid cell, the smaller half will be filled. Also corners cannot divide a fluid cell. You may therefore need to refine the MESH locally, to be able to capture the geometry you'd like to represent. With respect to the heat transfer: The GEOMs are still in development, thus come with some limitations. I suggest to have a look at the user guide in the nightly builds, to get some of the most recent information on the capabilities implemented into FDS. For now, I would also suggest to use the OBST as much as possible. Hope this helps, have a nice day!

[@kartiniganesha6741]

@@firesimandcoding thank you so much for the insightful response. I have a question for a HRR calculation, if we have the scaled HRR measurements from the laboratory, which approach is more accurate to predict the full scale HRR based on scaled HRR?

[@firesimandcoding]

Hi @kartiniganesha6741 you're welcome! Could you please elaborate on which kind of experiment you are interested in and what you mean be "scaled HRR"? For large-/real-scale experiments, two common methods to determine the HRR are to calculate it from the combustible mass flow or from the oxygen consumption. With this I assume there is a room containing a gas burner, similar to the Steckler compartments, or the Singe Burning Item test. The combustible mass flow could be used for a gas burner, where one knows the heat of combustion of the gaseous species: HRR (kW) = mass flow (kg/s) * heat of combustion (kJ/kg) The oxygen consumption method is based on work by Huggett ("Estimation of rate of heat release by means of oxygen consumption measurements", onlinelibrary.wiley.com/doi/abs/10.1002/fam.810040202). There is also some discussion in the ISO 5660-1:2015(E) "Heat release rate (cone calorimeter method) ..." Is this what you are interested in?

[@kartiniganesha6741]

Hello @@firesimandcoding, thanks for the response , it's almost there. I will try to elaborate more. Let's say, we conduct the HRR measurements based on oxygen consumption with a cone calorimeter . Regularly the size of the material is small (kzbin.info/www/bejne/o5_dfKeeq9CGrpI) . The question is, can we scale up linearly the value of HRR for the tested materials? For instance the tested material's size is 15x15 cm. But, we need a scenario with the sizel of 15x15 metres with the same materials.

[@firesimandcoding]

Hi @kartiniganesha6741, typically the data from the cone calorimeter experiment is given in context of the exposed sample surface area. This leads to a heat release rate, or mass loss rate, per unit area, i.e. kW/m² or kg/m². Thus, the data is supposedly independent of the sample size. However, it is important to note that the data has the experiment setup baked into it. Consider that one would perform a cone calorimeter experiment with a radiative heat flux of 50 kW/m², from the heater to the sample surface. This value is typically kept constant throughout the whole experiment. If a flame forms, it will contribute further to the heat flux into the sample, by an unknown and also variable amount. During the test the sample might also deform, which may change the distance between heater and sample surface. Thus, the heat flux could vary by some amount. So, the HRR vs. time profile you get as an response from the experiment implicitly contains all of this. If you are sure that the full surface area receives the heat flux profile like the experiment, you could simply scale it up. Though, I have doubts that it works this straight forward in most cases, but might be better than nothing. FDS provides some mitigation measures for this. It is able to adjust the HRR based on the incoming heat flux. Please have a look at section "9.1.4 Scaling the Burning Rate by the Heat Flux" in the FDS-6.8.0 users guide (github.com/firemodels/fds/releases/download/FDS-6.8.0/FDS_User_Guide.pdf). There are also procedures to determine ignition temperatures for solids from cone calorimeter data. An overview is provided in the Ignition Handbook by Babrauskas (www.researchgate.net/publication/288833461_Ignition_Handbook), specifically procedures by Janssen, Quintiere and Tewarson (pages 260 to 265). We have also a brief discussion on using cone calorimeter data and determining the ignition temperature, similar to what is described above (Appendix D in www.mdpi.com/2571-6255/3/3/33). Just note that no heat flux adjustments are performed in the simulations -- if I remember correctly this was not yet implemented in the used FDS version. In general, I would suggest you have also a look into the "SFPE Handbook of Fire Protection Engineering" (www.sfpe.org/publications/handbooks/sfpehandbook) and the "Enclosure Fire Dynamics" book by Karlsson and Qunitiere (www.taylorfrancis.com/books/mono/10.1201/b22214/enclosure-fire-dynamics-second-edition-bj%C3%B6rn-karlsson-james-quintiere). Specifically, focus on heat release rates and design fires. Hope this helps!