Hydrostatic Pressure in Vertical Monophasic Pipe

wagnerqb · January 22, 2013, 23:05

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:
Gravity
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.

Thanks.
Wagnerqb

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.

Thankful;
Wagnerqb

January 22, 2013, 23:05	Hydrostatic Pressure in Vertical Monophasic Pipe	#1
wagnerqb New Member Wagner Queiroz Barros Join Date: Jan 2013 Posts: 13 Rep Power: 13	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: Gravity 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. Thanks. Wagnerqb

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January 29, 2013, 09:57		#2
wagnerqb New Member Wagner Queiroz Barros Join Date: Jan 2013 Posts: 13 Rep Power: 13	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?

January 30, 2013, 17:08		#3
chaosh New Member sp Join Date: Jul 2011 Posts: 23 Rep Power: 15	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 rhogh.

January 30, 2013, 17:50		#4
wagnerqb New Member Wagner Queiroz Barros Join Date: Jan 2013 Posts: 13 Rep Power: 13	I have already done it but it didn't work. My simulation does not converge when I set the density equals 0.

January 30, 2013, 17:57		#5
chaosh New Member sp Join Date: Jul 2011 Posts: 23 Rep Power: 15	What solution method are you using? For a simple flow problem like this, convergence should not be an issue. Can you provide more details?

January 30, 2013, 18:02		#6
wagnerqb New Member Wagner Queiroz Barros Join Date: Jan 2013 Posts: 13 Rep Power: 13	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.

January 30, 2013, 18:10		#7
chaosh New Member sp Join Date: Jul 2011 Posts: 23 Rep Power: 15	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

January 30, 2013, 20:32		#8
wagnerqb New Member Wagner Queiroz Barros Join Date: Jan 2013 Posts: 13 Rep Power: 13	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. Thankful; Wagnerqb