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

Constant Pressure Boundary Conditions

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 21, 2012, 14:27
Default Constant Pressure Boundary Conditions
  #1
New Member
 
Krishna
Join Date: Oct 2012
Posts: 3
Rep Power: 3
LeLouch16 is on a distinguished road
Hello, I am just beginning to learn CFD.
I seem to be stumped at this problem where i have to simulate an unsteady flow in a variable area duct (Quasi 1D flow), given constant inlet and outlet pressure. I do not understand how to implement the boundary condition .
Since constant pressure is the only condition that is specified, I cant find how it affects the other variables like density. It would be very helpful if someone could give me a push..
LeLouch16 is offline   Reply With Quote

Old   October 23, 2012, 15:46
Default
  #2
Senior Member
 
Chris DeGroot
Join Date: Nov 2011
Location: Canada
Posts: 387
Rep Power: 5
cdegroot is on a distinguished road
Hi, can you explain a bit more about your problem. Are you writing a code or using some software? I'm assuming it is compressible flow since you mentioned density. Did you know that specifying pressure on both inlet and outlet is not a very numerically stable way of applying boundary conditions?
cdegroot is offline   Reply With Quote

Old   October 24, 2012, 02:45
Default
  #3
New Member
 
Krishna
Join Date: Oct 2012
Posts: 3
Rep Power: 3
LeLouch16 is on a distinguished road
Hey, Thanks for replying

I am writing the code form scratch, and yes its a compressible flow, and i am also expecting a shock to form somewhere near the end. I am using Flux Vector Splitting to compute the flow.. I have been given the inlet and back pressures of the Nozzle, and initial distribution of density, Temperature and velocity. This is all i have..

I did not know that..
LeLouch16 is offline   Reply With Quote

Old   October 24, 2012, 09:00
Default
  #4
Senior Member
 
Chris DeGroot
Join Date: Nov 2011
Location: Canada
Posts: 387
Rep Power: 5
cdegroot is on a distinguished road
Congratulations on writing your own code. It is most robust if you can specify velocity or mass flow at the inlet and pressure at the outlet, but it sounds like that won't be possible. Alternatively, you can specify total pressure at the inlet and static pressure at the outlet, which is reasonably robust. Are the pressures that you have static or total pressures? You are also going to need some kind of boundary condition for temperature. If you just use Neumann conditions everywhere the temperature level is not constrained and probably won't converge. Most likely you are going to have to give an inlet temperature.
cdegroot is offline   Reply With Quote

Old   October 24, 2012, 09:08
Default
  #5
New Member
 
Krishna
Join Date: Oct 2012
Posts: 3
Rep Power: 3
LeLouch16 is on a distinguished road
Thanks, I'll see what I can do...
What I have are the static pressures, I think I'll start by assuming an inlet velocity
LeLouch16 is offline   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
Implementation of boundary conditions for FVM Tom Main CFD Forum 7 August 26, 2014 05:58
Pressure boundary conditions hiras FLUENT 20 August 6, 2014 03:02
Water subcooled boiling Attesz CFX 7 January 5, 2013 03:32
Pressure and Velocity boundary conditions rsmartins CFX 3 October 6, 2011 07:06
Hydrostatic pressure in 2-phase flow modeling (CFX4.2) HB &DS CFX 0 January 9, 2000 13:19


All times are GMT -4. The time now is 00:25.