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wagnerqb January 22, 2013 23:05

Hydrostatic Pressure in Vertical Monophasic Pipe
Hello everybody,

I am new at this forum and I have a problem,

I am modeling a vertical and bidimensional pipe with 10 meters lenght, and 0.1 meters radius, with water fluid. The water is running down along the pipe and I need to generate a hydrostatic pressure in my simulation.

Boundary Conditions:
up --> Velocity Inlet = 0.001 meters/second (Laminar)
left and right --> Wall
Down --> Pressure outlet = 0 Pa

Operation Conditions:
Y= -10 m/s;
Specified Operation Density = 0 Kg/m3
Reference Pressure Location = (0.05;10)

When I activate the gravity the simulation automaticly fails. I cannot generate a hydrostatic pressure with this flow.


wagnerqb January 29, 2013 09:57

Please anyone, this problem is driving me crazy.

I was thinking about the Navier-Stokes equation, this equation is not solved for a vertival pipe yet, maybe I am dealing with a transient problem, what do you think?

chaosh January 30, 2013 17:08

Go to operating conditions and check the box where its marked 'specified operating density'
You will need to set that to zero. You'll then see rho*g*h.

wagnerqb January 30, 2013 17:50

I have already done it but it didn't work. My simulation does not converge when I set the density equals 0.

chaosh January 30, 2013 17:57

What solution method are you using? For a simple flow problem like this, convergence should not be an issue. Can you provide more details?

wagnerqb January 30, 2013 18:02

I am using the default parameters for this simulation, like COUPLE, first order for the couples, but I have tried to change these parameters and my simulation crashed too.

chaosh January 30, 2013 18:10

1. Check your mesh (scale, for example - if it was made in inches, but read into fluent in meters)
2. Check the direction of your velocity input
3. For incompressible flow, just use outflow boundary condition
4. Use SIMPLE to solve your problem - lower the under-relaxation factors for 0.2 for pressure, 0.5 for momentum.
5. After you initialize the solution, before running, plot contours of total pressure - you should see the hydrostatic pressure component in there as well.
6. On a different note, why do you need to include hydrostatic pressure in this? Is flow moving in a direction opposite to gravity?

It would be easier to help if I knew the purpose of your simulation.
good luck

wagnerqb January 30, 2013 20:32

I am trying to simulate a vertical flow of water and air, I am interested in the transitions between the flow regimes, specialy dispersed in slug flow, so the hydrostatic pressure is so important.

I though that I had to star my problem using just water, to dominate the phenomena, and my next step is use the eulerian-eulerian, to simulate this flow. But I am having troubles to dominate the first part of the simulation.

If you send me you email adress, I can send you the .cas file, and you can help me easylier.


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