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-   -   Negative pressure in 2D problem (http://www.cfd-online.com/Forums/cfx/25233-negative-pressure-2d-problem.html)

Micgre February 14, 2008 04:58

Negative pressure in 2D problem
 
Hello world,

I tried to study the pression lost in a valve. To simplify, I tried to work in a 2D problem. You can see my model here :

http://img101.imageshack.us/img101/1...opimagemi4.png

My parameters are : - Air at 25C - Steady state - Inlet = Pressure at 2200Pa - Outlet = Mass air flow at 0.0009 kg/s - Symetry on both side

In the result, pressure on outlet is around -100000Pa !!!

When I tryed on an 3D model, with same parameters, the result are Ok.

Do you have any idea of this problem on 2D ?

Thanks a lot for your help

Micgre


Glenn Horrocks February 14, 2008 17:45

Re: Negative pressure in 2D problem
 
Hi,

Did you scale the mass flow rate to reflect the smaller area of the 2D model? For example, if you are modelling a channel 1 metre wide using a 2D flow with a 1mm wide slice, you will need to reduce the mass flow rates by a factor of 1000.

Glenn Horrocks

Micgre February 18, 2008 03:24

Re: Negative pressure in 2D problem
 
I already done this ratio :( I don't understand why this flow rate delta can create negative pressure ?

Thanks for your help.

Micgre February 21, 2008 11:45

Re: Negative pressure in 2D problem
 
I think my problem is from symetry because when I work with my 3D model and cut an half, I've got negative pressure...

But I don't understand why...


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