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-   -   absolute pressure changing at the inlet (http://www.cfd-online.com/Forums/fluent/124740-absolute-pressure-changing-inlet.html)

diamondx October 11, 2013 14:57

absolute pressure changing at the inlet
 
hey everyone,
I am launching a new case of simulation using the non premixed model. I fix my operating pressure to 366100 Pa. After some iterations, when i report the absolute pressure for the outlet, I found it to be 366100 Pa. and the inlet a little more higher. Why doesn't my inlet pressure equals 366100 Pa ?

thanks a lit

oj.bulmer October 14, 2013 06:03

If I am not missing something, isn't it obvious? Never used the non premixed model, but you would think that delta P across the inlet and outlet is responsible for flow?

diamondx October 15, 2013 12:44

Thanks for your response,
Well , I was hoping to get a delta P of course, but since my inlet pressure is 366100 Pa, the outlet should be lower than that.
instead I'm getting the 366100 Pa at the outlet.
I want my air to enter at 366100 Pa. Not sure if I'm clear,
Thanks again

macfly October 16, 2013 09:46

What are your BCs, velocity-inlet and pressure-outlet? Based on the pressure drop that you obtained, maybe you could set the inlet BC to pressure-inlet and the outlet to outlet-vent. In the outlet-vent settings, you adjust the Gauge Pressure according to the pressure drop you obtained initially, and Target Mass Flow Rate.

diamondx October 16, 2013 14:42

Thanks francois,
the BC i used for the inlet is "mass-flow inlet", I could set the outlet-vent in the outlet like you said. But I also would like to validate the Delta-p of the experiments so I kept it pressure outlet.
If I were to switch to pressure-inlet. what gauge total pressure should I input knowing that the operating pressure 366100 Pa and that's what I want for my entering air ? I suppose it's zero. Can someone validate my saying ? Even with those entry my mass flow will not be the one I want. I'm missing something here.

macfly October 16, 2013 14:50

Yes, gauge pressure 0 at inlet.

If you target mass flow rate at outlet and it converges to the targeted value, you will have the same mass flow rate at inlet. Even if there some fuel injection between inlet and outlet, you can do the calculation for the targeted mass flow rate at outlet. (unless there is some unknown infiltration/exfiltration...)

I have no idea if these settings converge well or not.

Keep me posted.

diamondx October 16, 2013 14:52

Great, I'll keep you posted.
Thanks a lot

diamondx November 5, 2013 12:38

Everything work fine now. Thanks a lot !!!


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