
[Sponsors] 
October 2, 2010, 11:48 
rho euation in rhoPisoFoam

#1  
Senior Member
Nilesh Rane
Join Date: Apr 2010
Posts: 122
Rep Power: 8 
Hi,
In rhoPisoFoam, the .c code includes rhoEqn.H file but the file is not in that folder. Is is getting included from some other common directory?? I am asking this because when i solve my simulation the rho equation is not getting solved, it seems. Can anyone tell me, what is the problem here?? Why the rho equation is not being solved?? Quote:
__________________
Imagination is more important than knowledge..


October 3, 2010, 21:06 

#2 
Senior Member
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,907
Rep Power: 27 
Search your OpenFOAM1.7.x/src directory for rhoEqn.H and you will find it. It is basically
solve(fvm::ddt(rho) + fvc::div(phi)); with explicit discretization of the divergence to avoid conservation errors. The fact you see residuals equal to zero means that the solution is exact, not that the equation is not solved. You are using the diagonal solver, which is direct, and gives you the exact solution of the linear system. Best,
__________________
Alberto Passalacqua GeekoCFD  A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats. OpenQBMM  An opensource implementation of quadraturebased moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. 

October 4, 2010, 06:07 

#3 
Senior Member
Nilesh Rane
Join Date: Apr 2010
Posts: 122
Rep Power: 8 
But No of iterations is also 0.
__________________
Imagination is more important than knowledge..


October 4, 2010, 12:02 

#4 
Senior Member
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,907
Rep Power: 27 
This is really basic
How many iterations do you need to obtain the exact solution of a linear system with a direct solver? The answer is zero, because the method is not iterative You basically can easily do that with the Thomas algorithm for whatever tridiagonal system (or block tridiagonal). Check a book on the topic to have the details. Best,
__________________
Alberto Passalacqua GeekoCFD  A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats. OpenQBMM  An opensource implementation of quadraturebased moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. 

October 5, 2010, 07:44 

#5 
Senior Member
Nilesh Rane
Join Date: Apr 2010
Posts: 122
Rep Power: 8 
Ohh...OF takes it in that sense. I was thinking on different line. I thought if you solve an equation (or rather a system of equations in turn) 1 time then No of Iterations should be 1 and so on...
I do know about TDMA.. have used it in my UG assignments.. Thanks a lot..
__________________
Imagination is more important than knowledge..


Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Low Mach number Compressible jet flow using LES  ankgupta8um  OpenFOAM Running, Solving & CFD  7  January 15, 2011 14:38 
rhoPisoFoam stability problems at low Mach  ivan_cozza  OpenFOAM  1  October 1, 2010 11:03 
How to define and calculate LES variables rhoPisoFoam  Jotazeld  OpenFOAM  0  July 26, 2010 05:21 
help: rhoPisoFoam to compressibleInterFoam  jason.ryon  OpenFOAM  0  March 8, 2010 13:45 
Error log  vw.cfd  OpenFOAM  6  August 7, 2009 05:44 