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

Boundary conditions

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

Reply
 
LinkBack Thread Tools Display Modes
Old   March 4, 2006, 15:50
Default Boundary conditions
  #1
Ruchi
Guest
 
Posts: n/a
Is it possible to impose 2 boundary conditions on the same boundary? And impose no BC on an outlet? I mean, for example I have a geometry with an inlet and 2 outlets. I want to fix the velocity and the presure of my inlet, pressure of an outlet and let the software calculate the corresponding pressure at the second outlet. Can anyone please help me?
  Reply With Quote

Old   March 5, 2006, 16:04
Default Re: Boundary conditions
  #2
Eike
Guest
 
Posts: n/a
You have to define at least one characteristic for every boundary, because the conditions on your second outlet will influence the flow as well.
  Reply With Quote

Old   March 5, 2006, 21:46
Default Re: Boundary conditions
  #3
TB
Guest
 
Posts: n/a
If you specified inlet velocity & outlet static pressure, inlet static pressure will be part of the solution. No point to make redudant BC. Besides, I have doubt if you can leave one of your outlet boundary undefined anyway. If you aren't sure, just give it a go and see if the solver accept this condition.
  Reply With Quote

Old   March 5, 2006, 22:07
Default Re: Boundary conditions
  #4
Ruchi
Guest
 
Posts: n/a
Yes, its right that I can't leave a boundary condition undefined.

In real world I can measure the pressure at my outlet using a pressure gauge. All I want to do is to mimick the pressure gauge at my outlet to get the outlet pressure. Do you have any suggestion how a pressure gauge can be represeted in the software? I can't do real experiments at this stage because my real device requires microfabrication in clean room.
  Reply With Quote

Old   March 5, 2006, 22:12
Default Re: Boundary conditions
  #5
TB
Guest
 
Posts: n/a
Remember you have to define the reference pressure? If you measure pressure with respect to atm, just define reference pressure as atm pressure. All pressure calculations will be based on this reference pressure.
  Reply With Quote

Old   March 5, 2006, 22:26
Default Re: Boundary conditions
  #6
Ruchi
Guest
 
Posts: n/a
Let me re-phrase my question. May be I wasn't so clear. How do we measure pressure at a point in a pipe? Using a pressure gauge, right? What I meant is that my outlet is connected to a pressure gauge and I want to record what is the reading of my pressure gauge.
  Reply With Quote

Old   March 6, 2006, 07:56
Default Re: Boundary conditions
  #7
siv
Guest
 
Posts: n/a
Hello Ruchi, If you want to measure any variable at some point create monitor points and solve. then you can even find the variation of your variable with time step.
  Reply With Quote

Old   March 6, 2006, 08:11
Default Re: Boundary conditions
  #8
Ruchi
Guest
 
Posts: n/a
Hi,

Thanks for the suggestion.

But I am wondering if I have set my pressure at the outlet to atmospheric pressure, I should measure the pressure to be the same as what I have set. Thats the reason why I didn't want to set the outlet pressure and let the software calculate it for me. And because I have 2 outlets, I don't know how the mass flow will split in each of the outlets.
  Reply With Quote

Old   March 6, 2006, 14:58
Default Re: Boundary conditions
  #9
Eike
Guest
 
Posts: n/a
I think your system is under-determind, if you define only the pressure of one outlet. How do you want to run your experiments without setting the pressure of both outlets?

  Reply With Quote

Old   March 7, 2006, 01:14
Default Re: Boundary conditions
  #10
TB
Guest
 
Posts: n/a
Try look at user manual about "boundary condition" and think about how those NS equations are being solved. I remember there're suggestion about what type of inlet/outlet boundary condition you can use. For a simple flow, you need a driving force, say static pressure drop, for flow to occur. Unrealistic boundary condition gives unrealistic solution. You need to give solver some idea about the conditions at outlet to get a "unique" solution.
  Reply With Quote

Old   March 8, 2006, 22:44
Default multiphase domain
  #11
Avillyd
Guest
 
Posts: n/a
HI..

I'm doing simulation in engine chamber now and i found some difficulties. I appreciate whoever can help me to solve the problem. Here is the problems i've faced.

1) How to define two material in a chamber. i not found the solution to define inlet air as air idea gas and inlet fuel as fuel. What i have is, Cfx define both condition is already in a chamber. What i need is they mixing after we define air anfd fuel are come in.

Can anybody help me? i really need to solve this problem immediately..

tq
  Reply With Quote

Old   March 14, 2006, 06:33
Default Re: Boundary conditions
  #12
M
Guest
 
Posts: n/a
Hi ,

I understand what you are trying to say, how about if you have your pipe in a box or enclosure. Instead of having an outlet have a hole so that flow will be coming into the inlet and then out of a hole into some sort of enclosure(box) maybe you could set a pressure condition on one of the far faces of the enclosure and this way you can determine the pressure at the hole.

M
  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
symmetry boundary conditions in cfx lost.identity CFX 41 May 22, 2013 07:21
Impinging Jet Boundary Conditions Anindya Main CFD Forum 24 January 11, 2012 13:40
OpenFOAM Variable Velocity Boundary Conditions NickolasPl OpenFOAM Programming & Development 2 May 19, 2011 05:37
boundary conditions and mesh exporting vaina74 Open Source Meshers: Gmsh, Netgen, CGNS, ... 2 May 27, 2010 09:38
Trimmed cell and embedded refinement mesh conversion issues michele OpenFOAM Other Meshers: ICEM, Star, Ansys, Pointwise, GridPro, Ansa, ... 2 July 15, 2005 04:15


All times are GMT -4. The time now is 00:52.