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-   -   Hey Fluent Guru's!! Need help here! (http://www.cfd-online.com/Forums/fluent/41591-hey-fluent-gurus-need-help-here.html)

Amr July 3, 2006 21:15

Hey Fluent Guru's!! Need help here!
 
Hi,

I need to initialize a transient simulation of a fire model inside a compartment. Now, I don't really know what proper value to assign as a first value for K,e or w -in case of k-w model- for this room. The air inside the room is initially stangnant. Any ideas??

Cheers, Amr


Razvan July 4, 2006 07:53

Re: Hey Fluent Guru's!! Need help here!
 
Of course, one is tempted to initialize using 0 everywhere, but that is not recomandable (phisically it makes all sense, but numerically it can generate instability in first iterations, even divergence). So, simply initialize using small values, which will quicly dissipate into the grid in the first 2-3 time steps, like 0.001 for k and 0.1 for e or w. It really doesn't matter that much!

Razvan

AR Smith July 4, 2006 18:29

Re: Hey Fluent Guru's!! Need help here!
 
physically it does not necessarly make sense, you can have residual turbulence in a big room where people are walking, breathing, working, etc...

Razvan July 5, 2006 02:15

Re: Hey Fluent Guru's!! Need help here!
 
We are talking about a fire simulation here, which I know from Amr that was simulated experimentally first, and physically speaking, there were no people in that room at the time of the experiment, hence no residual turbulence caused by walking, breathing, working, etc... Anyway, we must agree on something: without movement turbulence cannot exist (brownian motion is NOT turbulence), and that is what Amr said were the initial conditions. Thank you for your intervention, you would have been perfectly right if there were any people in that room, but it is not the case here.

Best wishes, Razvan


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