[nhp12]

Hello, I hope you are all doing well.

I've been doing analysis of a 20MW fire in the road tunnel, with the vertical gradient of around 2.5%, expecting the bouyancy force generated by the temperature difference caused by the fire to form a certain level of airflow towards the portal of the uphill side.

However, I am confused about Boussinesq Parameters and Variable-density parameters. I have read the user's guide and it says for bouyancy-driven flow problems, I have to activate either boussinesq model or operating density.

I have very limited thoerical base, so I am struggling to understand all those mathematical terms, so I looked through some papers about fire analysis in the tunnel for a case study, and I found one paper stating that the Boussinesq approximation is not suitable for tunnel fire cases as it creates large rise/ increase in temperature. So I tried activating a specified operating density and I set the density of air at the initial state(at the initialized temperature) and the result seems to make sense for me. But I've been told to several people that I should not use specified operating density options for the fire case in the tunnel.

I wish I could study more and find out the right answer by myself but this project has to be done within this week. Anyone's advise and idea will be very much appreciated. I’m on a strict deadline and am desperate for any sort of help or direction, hopefully someone on this forum can give me some guidance or tips. Thank you.