# Pressure outlet

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 July 11, 2006, 23:01 Pressure outlet #1 Vidya Guest   Posts: n/a Hi, I want to retain my outlet Boundary Condition to be specified as being at atmospheric pressure. For this, I chose the face that is to be the outlet, went to BC in Fluent, selected the PRESSURE OUTLET option, and just selected OK to whatever the default was. Isn't the default set to atmospheric pressure? then why does Fluent give error messages? Since the deafult gage pressure is zero, the pressure is atmospheric. So what could be the problem? Thanks.

 July 12, 2006, 13:37 Re: Pressure outlet #2 Vivek Guest   Posts: n/a There shouldn't be any problem. What error message did u get?

 July 12, 2006, 14:11 Re: Pressure outlet #3 Vidya Guest   Posts: n/a It just gave a value of zero velocity at every point in the flow domain, which is absolutely meaningless. Also, all other parameters like pressure etc were either zero, when it actually shouldn't be, or sometimes goes to zero, which is again absurd. Will specifying pressures at both the inlet and outlet help solve the problem? Thanks

 July 12, 2006, 15:08 Re: Pressure outlet #4 Vivek Guest   Posts: n/a whats ur inlet boundary condition now? what problem are you trying to solve?

 July 12, 2006, 17:10 Re: Pressure outlet #5 Vidya Raja Guest   Posts: n/a I gave a steady input velocity of 0.175 m/s at the inlet. I want to retain the outlet at atmospheric pressure. The flow is laminar, and I'm trying to model blood flow. Is it possible to specify pressure BCs at both inlet and outlet? Then the inlet pressure is very small..... about 1.5 mm Hg. That's why I want to use the velocity at the inlet. I also have to run the case using an unsteady velocity.

 July 13, 2006, 12:00 Re: Pressure outlet #6 Vivek Guest   Posts: n/a You could do it either way. There shouldn't be any problem at all. Just make sure if there is an internal suface which you forgot to change from the default wall boundary condition. Its typically the reason for zero velocities

 July 13, 2006, 13:20 Re: Pressure outlet #7 Vidya Raja Guest   Posts: n/a I made that change, but the residuals never converge. However, the trends for all the residuals (continuity, x,y,z velocities) appears to be the same. Even after 17,000 iterations, the solution doesn't converge. What could be wrong now? Thanks, Vidya

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