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Old   June 12, 2013, 09:31
Default B.C Pressure inlet/outlet
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Omar
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Hello,

Is there any difference between a pressure outlet/inlet if we set it to 0 Pa?

I have a case where the calculation converge way better when i change a pressure outlet (0Pa) to pressure inlet (0Pa)

Thank you.

Omar
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Old   June 14, 2013, 11:13
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You'll have to be more specific. What are you modeling? What is driving your flow if your pressure differential is zero?
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Old   June 14, 2013, 16:26
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Thanks for answering, i have 2D wind tunnel car simulation with a vellocity inlet and all the others edges are: walls -> for the car, and pressure outlet for all the others .
The think is when i run the calculation like that it does not converge verry good "the continuity does not"
And when i replace one of the edges from pressure outlet "0Pa" to pressure inlet "0Pa", the model converge verry well and verry fast...

Thanks
Omar
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Old   June 16, 2013, 07:56
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Hi
if the other boundaries are something like as free stream ( or pressure far fild in the compressible flow), the pressure inlet with 0 Pa lead to better and faster convergence. I had some experience like this.

You should be care about no entering flow from these boundaries.
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Old   June 16, 2013, 15:48
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Hi, Thanks for answering
I only have pressure outlets and a vellocity inlet ...
I don't know why it's happening, i will take it as a rule until i find the difference between the pressure inlet/outlet at 0 Pa !

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Omar
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Old   June 17, 2013, 16:55
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A pressure inlet/outlet at 0 Pa is technically the same (differs by direction of flow). You have to make sure that you do not have air entering in through the pressure inlets.
The reason your simulation works well with the pressure inlet and not the outlet is cause there might be air entering your domain from these surfaces.
Do you get a lot of reversed flow when you pressure outlets?

Alternately you could use the farfield BC's, which are meant for your kind of problem

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Luke
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Old   July 13, 2013, 19:53
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mohammed rabie
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hi,
when you set the B.C as pressure inlet, it is total pressure
but when you set it as pressure outlet it is static pressure
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Old   July 14, 2013, 09:32
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Quote:
Originally Posted by mohamed rabie View Post
hi,
when you set the B.C as pressure inlet, it is total pressure
but when you set it as pressure outlet it is static pressure
I don't think so. Total pressure= static pressure+dynamic pressure and absolute pressure=gauge pressure+operating pressure. Every time we use the gauge pressure=0, it means that absolute pressure=operating pressure and it means, the outside of boundary is atmosphere(if we use the default for operating pressure=101325 pa)
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Old   July 19, 2013, 19:49
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Quote:
Originally Posted by flow_CH View Post
I don't think so. Total pressure= static pressure+dynamic pressure and absolute pressure=gauge pressure+operating pressure. Every time we use the gauge pressure=0, it means that absolute pressure=operating pressure and it means, the outside of boundary is atmosphere(if we use the default for operating pressure=101325 pa)
mmmmmm,

no problem at all, it is right, but the default in fluent is to take the pressure inlet value as total, but take the pressure outlet value as static , you can take a view in the fluent user guide.
and kindly please reply me,
I will wait for your reply
thanks
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