[hongyingli]

Hi,I am simulating a case with a vertical cylindrical column using Fluent 12. Water and air flows into the vertical cylindrical from the bottom to top.

The model I used is Eulerial multiphase model.

I have carried out two cases. One with gravity included in the simulation, the other one is without gravity force. Gravity force is opposite to the fluid flow direction.

For both of the case, I give the inlet boundary condition for water and air velocity as well as the air volume fraction. The outlet boundary is given by guage pressure with value of 0.

In the results without gravity force, the static pressure inlet is positive. This seems reasonable as the fluid flows from high pressure to low pressure (outlet static pressure is 0.)

However, in the results with gravity force, the static pressure inlet is negative. I don't know how to explain this? How can a fluid flows from low pressure to high pressure?

Can someone tell me what happend in this case?

What is the relationship between this static pressure and gauge pressure? Are they the same?

Thank you very much!