CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > CFX

Pressure pulsation in a pipe due to sudden opening

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   February 28, 2008, 06:55
Default Pressure pulsation in a pipe due to sudden opening
  #1
asder
Guest
 
Posts: n/a
I would like to check whether CFX is able to capture pressure pulsations, the phenomena so called water hammer or pressure surge. For this, I made a simple 1 m pipe length. At the entrance, I employed high pressure and at the exit I have imposed wall and pressure outlet conditions depending on time. For the few initial transient time steps, the outlet was a wall and then the boundary condition changed to pressure outlet to simulate sudden valve opening. From the results I observed that, if I choose small time steps, I only see a initial sharp pressure decrease and afterward pressure reaches a constant value. But If I choose, larger time steps, after the initial sharp pressure decrease, pressure pulsations were also induced.

For sure, such time step dependency is not correct. Is anybody knows this problem. Or anybody have expierence with simulation pressure surge problem in hydraulic pipelines with CFX?
  Reply With Quote

Old   February 28, 2008, 17:28
Default Re: Pressure pulsation in a pipe due to sudden ope
  #2
Glenn Horrocks
Guest
 
Posts: n/a
Hi,

I have done similar simulations in hydraulic oil systems. Yes, CFX can capture these waves. If you want to resolve the wave you need a fine time step. Keep in mind the acoustic velocity of water is something like 5000 m/s so you need fine enough timesteps to resolve waves of that velocity! You can use larger timesteps but the wave effect will be blurred and possibly loose simulation accuracy. Need to check how sensitive your simulation is to it.

Glenn Horrocks
  Reply With Quote

Old   March 1, 2008, 14:30
Default Re: Pressure pulsation in a pipe due to sudden ope
  #3
asder
Guest
 
Posts: n/a
Thank you very much for your reply. Could you please tell me bit more about your simulations. What was the booundary conditions, geometry, material properties you have used and so on.

Thanks in advance
  Reply With Quote

Old   March 2, 2008, 18:18
Default Re: Pressure pulsation in a pipe due to sudden ope
  #4
Glenn Horrocks
Guest
 
Posts: n/a
Hi,

It was a hydraulic oil circuit. It had no boundaries (except walls), the fluid motion was created by pistons moving. The geometry had a number of chambers connected by holes. The material properties were defined using a variable density, with the density being a function of pressure. The function was the definition of bulk modulus for a fluid. Search wikipedia for bulk modulus for more info.

Glenn Horrocks
  Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Can OpenFoam deal with pressure waves in pipe? coompressor OpenFOAM Running, Solving & CFD 1 October 12, 2011 08:20
My Revised "Time Vs Energy" Article For Review Abhi Main CFD Forum 2 July 9, 2002 09:08
Terrible Mistake In Fluid Dynamics History Abhi Main CFD Forum 12 July 8, 2002 09:11
fluid flow fundas ram Main CFD Forum 5 June 17, 2000 21:31
Hydrostatic pressure in 2-phase flow modeling (long) DS & HB Main CFD Forum 0 January 8, 2000 16:00


All times are GMT -4. The time now is 19:47.