CFD Online Logo CFD Online URL
Home > Forums > FLUENT

BC's In a Single Inlet/Outlet Pipe

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

LinkBack Thread Tools Display Modes
Old   April 24, 2001, 17:30
Default BC's In a Single Inlet/Outlet Pipe
J. Weiler
Posts: n/a
I have received a project on flow distribution through a 180 degree bend in a pipe. The mass flow rate, pressure, temperature, etc. are known for the inlet, so I have tried using a Mass-Flow-Inlet as my inlet boundary condition. The problem is that I need to examine the flow leaving the 180-degree bend (at the outlet)and I cannot figure out which boundary condition to apply. Essentially, nothing is known about the pipe outlet other than the diameter, and the goal is to distribute the flow as much as possible while mainaining a similar pressure. If anyone has any suggestions on which boundary conditions will yield a solution, I would certainly like to hear them. I have tried using an outflow and got immediate divergence. I can't use pressure outlet because the outlet conditions are unknown. I welcome all suggestions.
  Reply With Quote

Old   April 24, 2001, 18:03
Default Re: BC's In a Single Inlet/Outlet Pipe
John C. Chien
Posts: n/a
(1). A 180 degree bend pipe is likely to give you flow separation around the bend. (it depends on the pipe diameter and the radius of the bend). (2). So, you would like to move the exit of the pipe further down stream until the flow reattached and further developed. So, you can add a long pipe after the 180 degree bend. Flow separation will give you trouble in flow divergence. (3). The inlet condition can be uniform flow, fully developed flow or anything in between. All can have the same flow rate. So, you must specify your inlet flow condition. The code will not know which is your actual inlet condition. (4). So, use your mass flow rate to convert into the velocity profile at the inlet first, and then specify the velocity at the inlet. Uniform flow at the inlet and the fully developed flow at the inlet will give you different flow field around the bend. (5). With this ,my suggestion is: select the type of velocity profile at the inlet and calculate the velocity there as the input to the inlet condition. As for the exit condition, add a long pipe and specify the downstream condition there. By the way, flow field with internal flow separation will have convergence problem. You will have to deal with this part on your own.
  Reply With Quote

Old   April 25, 2001, 14:14
Default Re: BC's In a Single Inlet/Outlet Pipe
Xiao Hu
Posts: n/a
Looks like John Chien has already given you good advice on how to handle the situation here. I just want to add two more comments.

1) As for the 'flow field with internal flow separation will have convergence problem', I agree to some extent. However, as long as you give good initial conditions to start with, it should work fine.

2) Don't worry about the mass flow inlet too much. John was right there. However, I don't think it is necessary to convert into velocity profile at the inlet, unless you know the spacial distritution. I would just keep the mass flow inlet.
  Reply With Quote

Old   April 25, 2001, 21:30
Default Re: BC's In a Single Inlet/Outlet Pipe
J. Weiler
Posts: n/a
Thanks for the advice (John and Xiao). I will be running several simulations again tomorrow, and over the weekend and I will probably post the outcome early next week. In the mean time, I welcome any additional information you would like to pass on. Thanks ~Justin
  Reply With Quote


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
Problems with Cyclic & init. BCs for turbulent (k-eps) pipe flow florian_krause OpenFOAM 3 December 1, 2012 05:11
pipe flow with noozle - ? on BC's mediode Main CFD Forum 2 March 14, 2011 11:31
BCs in an FSI simulation of a flexble pipe vivekcfd OpenFOAM 10 January 8, 2010 05:14
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

All times are GMT -4. The time now is 00:16.