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

p, p_rgh and buoyant pressure

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

Like Tree1Likes
  • 1 Post By Ahmed Khattab

Reply
 
LinkBack Thread Tools Display Modes
Old   January 9, 2013, 17:39
Default p, p_rgh and buoyant pressure
  #1
Senior Member
 
Ahmed Khattab's Avatar
 
ahmed
Join Date: Feb 2010
Posts: 161
Blog Entries: 1
Rep Power: 7
Ahmed Khattab is on a distinguished road
Dear foamers,

why we define p, and p_rgh in some cases and don't define only one?

what is the difference in buoyant pressure boundary condition?

thanks in advance.
Ahmed Khattab is offline   Reply With Quote

Old   January 11, 2013, 10:33
Default
  #2
Member
 
Jianye Xia
Join Date: Mar 2009
Posts: 32
Rep Power: 8
bioexplore is on a distinguished road
I have the same question, can anyone help to explain these items?
bioexplore is offline   Reply With Quote

Old   January 11, 2013, 17:05
Default
  #3
Senior Member
 
Join Date: Nov 2012
Posts: 168
Rep Power: 4
hz283 is on a distinguished road
Hi,

According to my understanding, p is the total pressure, p_rgh is the hydrodyunamic pressure, actually, there should another pressure-therdynamic pressure. For low speed flows or for low ma assumption, p=rho*g*h + thermodynamic pressure. For compressible cases, p=rho*g*h + thermodynamic pressure + p_rgh. In the former case, the pressure appearring in EoS and the pressure appearring in momentum are not the same quantity. If we do not take the boyuance, rho*g*h can be removed.

We can also call the thermodynamic pressure as background pressure.
hz283 is offline   Reply With Quote

Old   January 23, 2013, 05:16
Default
  #4
Senior Member
 
Ahmed Khattab's Avatar
 
ahmed
Join Date: Feb 2010
Posts: 161
Blog Entries: 1
Rep Power: 7
Ahmed Khattab is on a distinguished road
Hi every body,

we all know that p = p_rgh + rho*g*h. but it this case both p, p_rgh are defined, so

which variable is calculated from the other, we can define only one. the other

question which one of them is used in N.S equations or energy eqn (i noticed that

p_rgh is used). another thing we know that p expresses total pressure and rgh

expresses hydrostatic pressure, so the difference expresses the dynamic pressure

which can be used for calculation velocity which already an input. I'm really confused ??
thanks
Ahmed Khattab is offline   Reply With Quote

Old   January 23, 2013, 14:16
Default
  #5
Senior Member
 
Ahmed Khattab's Avatar
 
ahmed
Join Date: Feb 2010
Posts: 161
Blog Entries: 1
Rep Power: 7
Ahmed Khattab is on a distinguished road
Dear Foamers,



please read this abstract from release note of OF v1.7.0

Quote:
Modifications to multiphase and buoyant solvers

  • Multiphase and buoyant flow solvers now solve for , rather than the static pressure p. This change is to avoid deficiencies in the handling of the pressure force / buoyant force balance on non-orthogonal and distorted meshes.
  • Improvements to boundary conditions and pressure referencing in closed domains have been developed to avoid the problems encountered in previous attempts to decompose pressure for buoyant flow.


my question is if OPreplaced p by p_rgh why we still define p in input files.

thanks
mgg likes this.
Ahmed Khattab 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



All times are GMT -4. The time now is 22:09.