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

why UEqn.H of buoyantSimpleFoam has no gravity term?

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

Reply
 
LinkBack Thread Tools Display Modes
Old   January 14, 2013, 16:50
Default why UEqn.H of buoyantSimpleFoam has no gravity term?
  #1
Member
 
yijin Mao
Join Date: May 2010
Location: Columbia, MO
Posts: 45
Rep Power: 7
alundilong is on a distinguished road
This might be silly question, but it confused me a lot..
these snippet code comes from buoyantSimpleFoam of OpenFOAM-2.1.1
3 tmp<fvVectorMatrix> UEqn
4 (
5 fvm::div(phi, U)
6 + turbulence->divDevRhoReff(U)
7 );
8
9 UEqn().relax();
10
11 if (simple.momentumPredictor())
12 {
13 solve
14 (
15 UEqn()
16 ==
17 fvc::reconstruct
18 (
19 (
20 - ghf*fvc::snGrad(rho)
21 - fvc::snGrad(p_rgh)
22 )*mesh.magSf()
23 )
24 );
25 }
shouldn't be this?
3 tmp<fvVectorMatrix> UEqn
4 (
5 fvm::div(phi, U)
6 + turbulence->divDevRhoReff(U)
7 );
8
9 UEqn().relax();
10
11 if (simple.momentumPredictor())
12 {
13 solve
14 (
15 UEqn()
16 ==
17 fvc::reconstruct
18 (
19 (
20 - ghf*fvc::snGrad(rho)
21 - fvc::snGrad(p_rgh)
22 )*mesh.magSf()
23 )
24 + rho*g
25 );
25 }
alundilong is offline   Reply With Quote

Old   January 14, 2013, 17:38
Default
  #2
Senior Member
 
akidess's Avatar
 
Anton Kidess
Join Date: May 2009
Location: Delft, Netherlands
Posts: 919
Rep Power: 17
akidess will become famous soon enough
No, the gravity term is hidden in between the usage of p_rgh and ghf*snGrad(rho). There is a thread on the forum with the derivation.
__________________
*On twitter @akidTwit
*Spend as much time formulating your questions as you expect people to spend on their answer.
*Help define the OpenFOAM stackexchange Q&A site: http://area51.stackexchange.com/prop...oam-technology
akidess is offline   Reply With Quote

Old   January 14, 2013, 18:12
Default
  #3
Senior Member
 
mturcios777's Avatar
 
Marco A. Turcios
Join Date: Mar 2009
Location: Vancouver, BC, Canada
Posts: 725
Rep Power: 18
mturcios777 will become famous soon enough
For bouyancy driven flows that is why we use p_rgh instead of p. If prgh = p + rho*g*h, then when we do grad p in the NS equations we get grad(p) and rho*g. I don't do a lot of buoyancy driven flow so I'm not 100% on the notation.
mturcios777 is offline   Reply With Quote

Old   January 14, 2013, 18:14
Default
  #4
Member
 
yijin Mao
Join Date: May 2010
Location: Columbia, MO
Posts: 45
Rep Power: 7
alundilong is on a distinguished road
thanks for your reply.
I derived, but may not correctly, so I did not see the term of rho*gravity.
How can I find that thread? some keywords are quite helpful.
alundilong is offline   Reply With Quote

Old   January 14, 2013, 18:18
Default
  #5
Member
 
yijin Mao
Join Date: May 2010
Location: Columbia, MO
Posts: 45
Rep Power: 7
alundilong is on a distinguished road
Quote:
Originally Posted by mturcios777 View Post
For bouyancy driven flows that is why we use p_rgh instead of p. If prgh = p + rho*g*h, then when we do grad p in the NS equations we get grad(p) and rho*g. I don't do a lot of buoyancy driven flow so I'm not 100% on the notation.
Thanks! I got the idea. I mistakenly took grad(rho*g*h) = grad(rho)*g*h without caring rho*g*grad(h), which equals to rho*g. Shame on me!
alundilong is offline   Reply With Quote

Old   January 15, 2013, 03:53
Default
  #6
Senior Member
 
akidess's Avatar
 
Anton Kidess
Join Date: May 2009
Location: Delft, Netherlands
Posts: 919
Rep Power: 17
akidess will become famous soon enough
Quote:
Originally Posted by alundilong View Post
thanks for your reply.
I derived, but may not correctly, so I did not see the term of rho*gravity.
How can I find that thread? some keywords are quite helpful.
I think it was this one:
Problems in understanding BuoyantBoussinesqSimpleFoam
__________________
*On twitter @akidTwit
*Spend as much time formulating your questions as you expect people to spend on their answer.
*Help define the OpenFOAM stackexchange Q&A site: http://area51.stackexchange.com/prop...oam-technology
akidess is offline   Reply With Quote

Old   October 22, 2013, 13:35
Default
  #7
New Member
 
Christiano Molossi
Join Date: Sep 2013
Posts: 10
Rep Power: 3
m.Chrsitiano is on a distinguished road
Hello!

I'm new to OpenFOAM, I started using about 1 month ago. And I have created and account here just now. So i didn't know if it was better to create a new topic or just replay an old one since my doubt is related to this topic.

So, I'm working on a simulation with the twoLiquidMixingFoam solver. And just like the UEqn.H posted here before, there is this: * mesh.magSf().
I would like to know what it is, what does it for? What this meaning?

Besides this, I want to learn the mathematical modelling form OpenFOAM, for example, in twoLiquidMixingFoam, what is the equations that the solver use to run? If someone could me introduce to a book or anything that may help me to understand the math from this software I would be very thankful.

Best regards!
m.Chrsitiano 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
mass source term in buoyantSimpleFoam OMN OpenFOAM 1 April 30, 2014 06:49
Gravity source term in PisoFoam DanM OpenFOAM Running, Solving & CFD 4 May 24, 2013 11:30
Gravity source term in PisoFoam DanM Main CFD Forum 0 November 28, 2012 13:59
Laplacian term missing in simpleFoam - UEqn.H Balakrshnan Ramakrishnan OpenFOAM 2 April 5, 2011 10:58
ATTENTION! Reliability problems in CFX 5.7 Joseph CFX 14 April 20, 2010 15:45


All times are GMT -4. The time now is 17:35.