
[Sponsors] 
July 23, 2013, 19:12 
Extra terms in turbulence model transport equations

#1 
Senior Member
Join Date: Mar 2010
Location: Cape Town, SA
Posts: 156
Rep Power: 9 
Hi,
I have been working on rewriting some parts of the kOmegaSST turbulence model, and recently realised there are some 'extra' terms in the transport equations for k and omega, notably  for omega: Code:
tmp<fvScalarMatrix> omegaEqn ( fvm::ddt(omega_) + fvm::div(phi_, omega_)  fvm::Sp(fvc::div(phi_), omega_)  fvm::laplacian(DomegaEff(F1), omega_) == gamma(F1)/nut_*min(G, c1_*betaStar()*k_*omega_)  fvm::Sp(beta(F1)*omega_, omega_)  fvm::SuSp ( (F1  scalar(1))*CDkOmega/omega_, omega_ ) ); Code:
tmp<fvScalarMatrix> kEqn ( fvm::ddt(k_) + fvm::div(phi_, k_)  fvm::Sp(fvc::div(phi_), k_)  fvm::laplacian(DkEff(F1), k_) == min(G, c1_*betaStar()*k_*omega_)  fvm::Sp(betaStar()*omega_, k_) ); I have been using a combination of references, but these do not appear in any of them, so they must be an openFoam programming peculiarity. Does anyone know / could anyone explain where these terms come from / why we have them in the eqns? thanks very much in advance much appreciated jonathan 

July 23, 2013, 20:59 

#2 
Senior Member
Daniel P. Combest
Join Date: Mar 2009
Location: St. Louis, USA
Posts: 596
Rep Power: 20 
This has been discussed in several places
But it is one of my favorite things in fluid mechanics for some reason . The definition of the advection operator is where the left side is the conservative form and the right side is the primitive form ( according to anishtain4 from gas dynamics lingo). The use if this term Code:
 fvm::Sp(fvc::div(phi_), k_) Code:
fvm::SuSp(fvc::div(phi_),k_) Code:
fvc::div(phi_) EDIT: There is actually a little bit of a discussion in "Computational Methods for Fluid Dynamics" by Ferziger and Peric' (3rd edition) on page 162 referring to the conservation of the kinetic energy equation. Last edited by chegdan; August 22, 2013 at 16:37. Reason: Added more information and a literature source and forgot a dot product 

August 14, 2013, 09:24 

#3  
Senior Member
Join Date: Mar 2010
Location: Cape Town, SA
Posts: 156
Rep Power: 9 
Hi Daniel,
apologies for the slow reply here  i saw your post and it helped a lot, however, things have been quite hectic this side, hence the late thanks. again, thanks for your help  much appreciated jonathan Quote:


August 19, 2013, 11:01 

#4 
Senior Member
Daniel P. Combest
Join Date: Mar 2009
Location: St. Louis, USA
Posts: 596
Rep Power: 20 
No worries, I enjoy discussing this topic. If anyone else has some thoughts that could expand this information I would love to hear about it. I can always learn more on the topic!


Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Define new turbulence model in Fluent  micro11sl  Fluent UDF and Scheme Programming  55  October 27, 2016 17:25 
Wrong calculation of nut in the kOmegaSST turbulence model  FelixL  OpenFOAM Bugs  27  March 27, 2012 09:02 
Editing Turbulence Model Terms  Josh  CFX  0  January 18, 2011 19:04 
PRoduction terms of a turbulence modeL  nada  FLUENT  1  December 30, 2008 23:40 
Advanced Turbulence Modeling in Fluent, Realizable kepsilon Model  Jonas Larsson  FLUENT  5  March 13, 2000 04:27 