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Old   December 29, 2015, 18:34
Default Pressure in a pipe
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I'm new in he forums and I'm currently learning to use Fluent ANSYS. I've gone through a lot of tutorials and right now I'm having problems with the most basic fluid calculations.

My problem is a cylinder pipe along the Z axis, the diameter is 1 meter and the lenght is 10 meters. The fluid is water and I have selected a velocity inlet of 1 m/s and a pressure outlet of 0 Pa. I'm considering the effects of gravity and I'm trying to test the Bernoulli equation, from which I should get a gauge pressure of around -98000 Pa, but instead of the expected value, I'm getting 67 Pa at the inlet. The model I'm using is Standard k-e.

The operating pressure is 0 Pa. I know this is really low level, but I can't find the mistake.

Thanks in advance

Last edited by JackTs; December 31, 2015 at 13:53.
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Old   January 3, 2016, 11:15
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Alright! I solved the problem. The operating density was disabled and gravity wasn't taken into account.

But I have another problem. I have modeled a pipe that splits into 3 different pipes, and I have set a velocity inlet and 3 pressure outlets. After reaching convergence I check the vectors of my outlets and it seems like 1 of them is working as an inlet, which I know it's impossible. Any help?

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Old   January 4, 2016, 00:28
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If you could post some images, that would help evoking a precise response.. are the BCs and operating conditions same as mentioned in your first post??
However, as an initial guess from what you mention, it seems like there is reversed flow in the mentioned outlet, you could try moving the outlet boundary further to avoid capturing flow circulations at the outlet boundary.. again, pictures of your model would help..
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Old   January 10, 2016, 08:06
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Thanks for your answer. I'm on a trip so I can't attach anything but a paint scheme, which I hope is enough.

The problem is related to the first one. It's a pipe system with 1 inlet and 3 outlets with a difference in height. The outlets are inside a water tank, and from bernoulli equation, I can easily calculate the static pressure in these points.

My inlet is defined as a velocity inlet, 0.6 m/s. All my outlets are defined as pressure outlets. Pressure outlet at top would be 2205 Pa, Pressure outlet at mid would be 6320 Pa and pressure outlet at bot would be 10430 Pa.

Using this boundary conditions, I get that the fluid at top is getting inside the domain instead of exiting it.
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