# B.C Pressure inlet/outlet

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 June 12, 2013, 08:31 B.C Pressure inlet/outlet #1 New Member   Omar Join Date: May 2013 Posts: 7 Rep Power: 5 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

 June 14, 2013, 10:13 #2 Senior Member   Join Date: Mar 2009 Location: Indiana, US Posts: 185 Rep Power: 9 You'll have to be more specific. What are you modeling? What is driving your flow if your pressure differential is zero? Regards Luke

 June 14, 2013, 15:26 #3 New Member   Omar Join Date: May 2013 Posts: 7 Rep Power: 5 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

 June 16, 2013, 06:56 #4 New Member   Yaser Join Date: May 2013 Location: I. R. Iran, Tehran Posts: 20 Rep Power: 5 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.

 June 16, 2013, 14:48 #5 New Member   Omar Join Date: May 2013 Posts: 7 Rep Power: 5 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 ! Thanks Omar

 June 17, 2013, 15:55 #6 Senior Member   Join Date: Mar 2009 Location: Indiana, US Posts: 185 Rep Power: 9 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 Regards Luke

 July 13, 2013, 18:53 #7 New Member   mohammed rabie Join Date: May 2012 Location: Egypt Posts: 6 Rep Power: 6 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

July 14, 2013, 08:32
#8
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Saeed
Join Date: Jan 2013
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Quote:
 Originally Posted by mohamed rabie 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)

July 19, 2013, 18:49
#9
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mohammed rabie
Join Date: May 2012
Location: Egypt
Posts: 6
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Quote:
 Originally Posted by flow_CH 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.
thanks

 Tags boundary conditions, fluent, pressure

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