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

modifing equations in the solver

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

Reply
 
LinkBack Thread Tools Display Modes
Old   May 15, 2012, 14:37
Default modifing equations in the solver
  #1
New Member
 
Join Date: Aug 2011
Posts: 11
Rep Power: 5
insta is on a distinguished road
Hello
Ive a question about the non-linear term (convection term) in N.S equations : (u*nabla)u
I want to modify this term into : ((u+u0)*nabla)(u+u0)
I mean u=u+u0
where u0 is defind as some known function ,
can someone please give me a direction on how to do this?

ThankYou
insta is offline   Reply With Quote

Old   May 16, 2012, 01:50
Default
  #2
Senior Member
 
Bernhard
Join Date: Sep 2009
Location: Delft
Posts: 790
Rep Power: 12
Bernhard is on a distinguished road
Did you derive what the discretized equation should look like? Maybe you can treat all the terms that are not u*nabla u as a source?

By the way, what is the physics in this approach? It seems a bit weird here? Maybe you want to use u0 as initialization?
Bernhard is offline   Reply With Quote

Old   May 16, 2012, 08:12
Default
  #3
New Member
 
Join Date: Aug 2011
Posts: 11
Rep Power: 5
insta is on a distinguished road
This form of equation represent the nonlinear dynamics of the perturbations only and u0 is the basic flow, so u is vector of perturbations and p is the fluctuated pressure only. in the convective term
((u+u0)*nabla)(u+u0): (u0*nabla)u0 is identically zero and the basic pressure plus the laplace term for u0 constitute the basic velocity u0, so also these terms falls , and then you get the dynamics of the perturbations

Thanks for the advice I will try to understand your suggestion
insta is offline   Reply With Quote

Old   May 16, 2012, 08:34
Default
  #4
New Member
 
Join Date: Aug 2011
Posts: 11
Rep Power: 5
insta is on a distinguished road
Hi bernard
About your suggestion
Quote:
Maybe you can treat all the terms that are not u*nabla u as a source
I believe that is not possible because there are terms like '(u0*nabla)u' and
'(u*nabla)u0' ,and these terms cannot be treated as source terms, because they are depended on 'u'.
Thus they have to be treated as implicit terms like (u*nabla)u.
So, how do we implement these modifications?
Should we modify the matrix only or also the PISO loop?

Thanks
insta is offline   Reply With Quote

Old   May 16, 2012, 09:27
Default look
  #5
Member
 
Lev
Join Date: Dec 2010
Posts: 31
Rep Power: 6
levka is on a distinguished road
Hey, guys have a look there
PISO algorithm for particular NS equation (special convection term)

Regards
Lev
levka 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
thobois class engineTopoChangerMesh error Peter_600 OpenFOAM 4 August 2, 2014 09:52
smoothSolver diverges - solution in using PBiCG solver? makaveli_lcf OpenFOAM Running, Solving & CFD 3 September 11, 2013 12:44
Using a user-defined solver in OF ozzythewise OpenFOAM Running, Solving & CFD 3 February 8, 2011 16:28
Getting too many iterations by velocity solving (aborting). Changing U - Solver? suitup OpenFOAM Running, Solving & CFD 0 January 20, 2010 08:45
free " ordinary differential equations solver" ztdep Main CFD Forum 2 March 21, 2006 02:58


All times are GMT -4. The time now is 03:46.