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xtarget April 19, 2011 05:55

Car Park simulation with Ansys 13.0
Hi everybody,

I've used fluent program simulate car park fire.We analysis the critic point of fire. the area of the park is 144000 m^2 and we use some jet fans to canalize the clean air and hot air.

We chose a car to burn; from the car surface applied 15 kg/s CO2 and 600 C degree hot air into the big car park domain. species transport model was used. But my problem is that; there is no reaction here so the 15 kg/s is extra for my domain. the real problem includes reaction (O2 and X material enters the reaction and CO2 and H2O consist at last, basicly)..and doesnt happen this additional mass flow (15 kg/s) it breaks my correct approximation for fans energy so i have to change jet fans (N/m^3) energy.

This occurs incorrect solution. For instance, when i used 15 kg/s CO2 mass flow 5.4 kg/s air is going out from the pressure outlet door whereas the fresh air has come into the domain not go out according to my fans... :confused:

what should i do for this extra CO2 mass flow i cant simulate the real reaction model transient. It has take more time. what is the right approximation for Critic time, steady-state analysis..

many thanks to read...

julien.decharentenay April 19, 2011 19:33

In real life, CO2 is produced by combustion of Air with the fuel of the car (be it the petrol or the materials of the car). So my best bet would be to suck back 15kg/s of Air (+CO2) by specifying a mass flow outlet the bottom of your car (that is if your car is lifted off the floor).

I would strongly advised that you keep track of the CO2 absorbed at the mass flow outlet to ensure that the amount of CO2 send to the car park is appropriate.

There are a couple of other alternatives way to model this problem that I can think of.

It looks to me that you are trying to demonstrate the jet fans are an appropriate solution for handling fire situation in a car park to be constructed. If this is the case, I would like to let you know that I am a bit worried that you do not have a methodology in place and proper guidance to demonstrate compliance with fire requirements.

Let me know where is the car park located if in Australia/Europe.

xtarget April 20, 2011 04:53

many thanks for reply.
it's in istanbul, Turkey.

actually we've completed analysis of this project with the other program. it is FDS. To correct location of jet fans our provider demonstrated some cases. there is no problem.

In our CFD departman, we have some different ideas about adding new things so we analysed... But about fire analysis we don't have much experiences about Fluent or CFX.

... and we tried your opinion before, to open outlet bottom of the car. But with the same value of mass flow sucking air from there is not completely accurate method. Because air movement changes and jet fans doesnt move the fresh air as we predicted.

If you have other experiences would you like to share this, with us ?

many thanks again...

julien.decharentenay April 20, 2011 19:04

I understand that you are trying to compare FDS with Fluent and/or CFX and you are trying to find an appropriate methodology to get similar conclusions.

I had the occasion to have a look at FDS documentation a few years ago, but can not remember much. My advise would be to have a very detailed look at FDS manual and Fluent/CFX manual to use similar modeling strategies in FDS and Fluent/CFX.

A few ideas that you may have investigated:
- Use a point or a volume source;
- Use a momentum source instead of a mass source;
- Track CO2 as a passive scalar (meaning that adding CO2 will not change your flow field, but you need to get back to first principles to get everything right). Note that heat will affect flow field.

That being said, I don't understand your comment "But with the same value of mass flow sucking air from there is not completely accurate method." What is the accurate method?

Good luck. Julien

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