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-   -   Change boundary condition in AVL FIRE (http://www.cfd-online.com/Forums/avl-fire/96293-change-boundary-condition-avl-fire.html)

neu January 18, 2012 12:19

Change boundary condition in AVL FIRE
 
Hi Guys,

I injected fuel from a small hole into a constant volume chamber in AVL FIRE v2008. The boundary condition for inlet is total pressure. After some millisecond I want to stop injection without stopping the program running. I think that I must change boundary condition from inlet to wall but I am not confident how can I do it? :confused:
Did anyone encounter with this problem hitherto?

Thanks,
neu

Rahul_W January 18, 2012 14:02

Hi
I dont know about AVL FIRE v2008 software but this may help you
you can simulate your problem with inlet boundary condition for required time step and then make inlet boundary condition to wall and initialize the problem with previous result and run again.

doki January 19, 2012 12:38

I am not sure if I get the problem correctly, but you SHOULD set a "physical" BC to get physical results.
I mean, you should think of what is happening in reality. as the pressure conditions are not "imposed" suddenly in the real case, you should use time-variable BCs in which the inlet pressure decreases from the maximum to ..... in a couple of time steps; e.g.:
1 100000
2 70000
3 50000
4 20000
5 ....
hope that helps :)

neu January 19, 2012 13:07

Change boundary condition in AVL FIRE
 
Hi doki,

What is the final pressure with passing the time?
As you know when injector is closed the inlet must be changed to wall not its pressure decreases. Because with decreasing the pressure the flow may exit from inlet if inlet pressure be smaller than inside pressure. Is it correct?

Best,


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