Two pressure inlets problem

Medison · August 22, 2012, 04:14

Hello!
Sorry for my English.

I have a problem with inlets in my model. I have 3 static pressure inlets and 1 static pressure outlet(i know that the pressure inlets are bad, but cant do anything about that). Two inlets have the same pressure and the other one have much higher pressure. High pressure inlet have no poblems. The problem with the low pressure inlets. After a certain amount of iterations (when the case starts to converge) one inlet cuts off (CFX places the wall in one inlet). I tried to put inlets as one BC and as different BCs with the same result. In theory the both low-pressure inlets should provide the same mass flow. The resulting mass flow (from Post) is equal with the calculated one but i cant understand why CFX tries to put all the mass flow from one inlet and cuts the other. Im using SST model with tetra mesh with boundary layer (i can use ICEM hexa but for the optimisation purpuses its easier to use tetra).

Can anyone give me an advise with this case?

Im adding the mass flow plot from CFX solver and streamlines from Post.
http://img515.imageshack.us/img515/6...solverplot.jpg
http://img820.imageshack.us/img820/1...ejpipescom.jpg

Thank you for your attention!

ghorrocks · August 22, 2012, 06:50

There is nothing wrong with pressure inlets. If you know the pressure at an inlet then you specify the boundary condition as a pressure inlet.

CFX is probably predicting reverse flow at one inlet. Have a close look in CFD-Post and try to see it. This might be real, or it might be just a numerical thing which will disappear with tighter convergence.

August 22, 2012, 04:14	Two pressure inlets problem	#1
Medison New Member George Sladkovsky Join Date: Aug 2012 Posts: 6 Rep Power: 13	Hello! Sorry for my English. I have a problem with inlets in my model. I have 3 static pressure inlets and 1 static pressure outlet(i know that the pressure inlets are bad, but cant do anything about that). Two inlets have the same pressure and the other one have much higher pressure. High pressure inlet have no poblems. The problem with the low pressure inlets. After a certain amount of iterations (when the case starts to converge) one inlet cuts off (CFX places the wall in one inlet). I tried to put inlets as one BC and as different BCs with the same result. In theory the both low-pressure inlets should provide the same mass flow. The resulting mass flow (from Post) is equal with the calculated one but i cant understand why CFX tries to put all the mass flow from one inlet and cuts the other. Im using SST model with tetra mesh with boundary layer (i can use ICEM hexa but for the optimisation purpuses its easier to use tetra). Can anyone give me an advise with this case? Im adding the mass flow plot from CFX solver and streamlines from Post. http://img515.imageshack.us/img515/6...solverplot.jpg http://img820.imageshack.us/img820/1...ejpipescom.jpg Thank you for your attention!

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August 22, 2012, 06:50		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,701 Rep Power: 143	There is nothing wrong with pressure inlets. If you know the pressure at an inlet then you specify the boundary condition as a pressure inlet. CFX is probably predicting reverse flow at one inlet. Have a close look in CFD-Post and try to see it. This might be real, or it might be just a numerical thing which will disappear with tighter convergence.