CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

basic question: Specifying Pressure for comressible solvers

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 13, 2010, 12:16
Default basic question: Specifying Pressure for comressible solvers
  #1
Senior Member
 
Nilesh Rane
Join Date: Apr 2010
Posts: 122
Rep Power: 7
nileshjrane is on a distinguished road
Hello All,

This is a basic question but just to clear the doubt once and for all:

The way we specify pressure for any compressible solver is with the units of [1 -1 -2 0..] i.e. p/rho. So we should specify the value of pressure as well after dividing p value by rho.

Meaning if i have p = 1MPa and rho = 10 kg/m3 then,

1) for compressible solver: p = 1/10 = 0.1
2) for incompressible solver: p = 10


Is this correct??
__________________
Imagination is more important than knowledge..

Last edited by nileshjrane; October 13, 2010 at 12:51.
nileshjrane is offline   Reply With Quote

Old   October 14, 2010, 05:00
Default
  #2
bb_
New Member
 
Join Date: Jul 2010
Posts: 20
Rep Power: 7
bb_ is on a distinguished road
I think you confused things here.

For incompressible solvers, you have to specify the kinematic pressure, i.e. p/rho units [0 2 2 0 0 0 0] wheres as for compressible solvers, the actual pressure p [ 1 -1 -2 0 0 0 0 ] is used.

Therefore, for your case with p = 1MPa and rho = 10 kg/m3:

1) for compressible solver: p = 1 MPa = 1e6
2) for incompressible solver: p = 1e6/10 = 1e5

However, when running incompressible simulations, only pressure differences count so you could also use 0 as a reference pressure. If you want to obtain real pressure differences, multiply the result obtained with foam (kinematic pressure) with rho.

Hope that helps.
bb_ is offline   Reply With Quote

Old   October 14, 2010, 10:16
Default
  #3
Senior Member
 
Nilesh Rane
Join Date: Apr 2010
Posts: 122
Rep Power: 7
nileshjrane is on a distinguished road
Hi,

You are damn right.. i was indeed confuse . I realised my mistake but didnt get time to edit my post. In fact i realised that mentioning p/rho is the only way to specify density in incomressible solvers.

Thanks for the reply.
__________________
Imagination is more important than knowledge..
nileshjrane 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
Pressure units in compressible solvers thekay OpenFOAM 2 January 12, 2010 09:48
basic question for pressure BC vivien OpenFOAM 0 November 23, 2009 06:01
How to read pressure at discrete points paka OpenFOAM 15 July 21, 2008 05:03
pressure gradient term in low speed flow Atit Koonsrisuk Main CFD Forum 2 January 10, 2002 11:52
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 20:03.