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

why totalPressure formulas are different?

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

Reply
 
LinkBack Thread Tools Display Modes
Old   April 10, 2013, 19:48
Default why totalPressure formulas are different?
  #1
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,186
Rep Power: 16
immortality is on a distinguished road
in header file of totalPressure in 2.2.0 version its explained briefly about categories of totalPressure bc.
Why for subsonic compressible flow we should use p0=p+.5*rho*U^2 and not the isentropic equation that includes mach in it like in gas dynamics texts?
immortality is offline   Reply With Quote

Old   April 11, 2013, 04:41
Default
  #2
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,186
Rep Power: 16
immortality is on a distinguished road
whats the reason of choosing different formula in subsonic and supersonic for compressible flow?
immortality is offline   Reply With Quote

Old   April 11, 2013, 08:37
Default
  #3
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,186
Rep Power: 16
immortality is on a distinguished road
it is what has been written in totalPressureFvPatchField.H
Code:
The modes of operation are set via the combination of \c phi, \c rho, and
    \c psi entries:
    \table
        Mode                    | phi   | rho   | psi
        incompressible subsonic | phi   | none  | none
        compressible subsonic   | phi   | rho   | none
        compressible transonic  | phi   | none  | psi
        compressible supersonic | phi   | none  | psi
    \endtable
and:
Code:
compressible subsonic:
        \f[
            p_T = p_0 + 0.5 \rho |U|^2
        \f]
        where
        \vartable
            p_T     | total pressure [Pa]
            p_0     | reference pressure [Pa]
            \rho    | density [kg/m3]
            U       | velocity
        \endvartable
while in all educational texts I have seen that this relation is for incompressible flow and for compressible flow we should use isentropic relations.
could anyone help me with this doubt on the concept?
immortality 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
totalPressure Boundary condition bastil OpenFOAM Running, Solving & CFD 4 July 4, 2013 09:09
Totalpressure Ansys Leuchte CFX 2 April 9, 2013 18:56
definition of totalPressure immortality OpenFOAM Running, Solving & CFD 7 March 15, 2013 05:38
BC settings to expand pressure on atmosphere - simpleFoam / totalPressure sErik OpenFOAM Running, Solving & CFD 1 June 15, 2011 02:49
totalPressure in rhoSonicFoam mihir1310 OpenFOAM Running, Solving & CFD 0 April 16, 2009 15:41


All times are GMT -4. The time now is 07:19.