
[Sponsors] 
September 10, 2008, 06:24 
Hi,
I try to analyse the ic

#1 
Member
Joern Bader
Join Date: Mar 2009
Posts: 33
Rep Power: 9 
Hi,
I try to analyse the icoFoam Solver. The Solver solves the Equation: ddt(U)+div(phi,U)Laplacian(nu,U)=grad(p) this themes seems to be a NavierStokesEquation but I miss an U at div(phi,U). The NavierStokes Equation I know sould be: ddt(U)+U*div(phi,U)Laplacian(nu,U)=grad(p) Does the U appear later in the discretisation or is it a variation of the NavierStokesEquation? Thx, Jörn 

September 10, 2008, 08:33 
No: the NS equation that _you

#2 
Senior Member
Gavin Tabor
Join Date: Mar 2009
Posts: 181
Rep Power: 9 
No: the NS equation that _you_ know is
ddt(U)+U*div(U)Laplacian(nu,U)=grad(p) Since div(u)=0 we can rearrange this as ddt(U)+div(U*U)Laplacian(nu,U)=grad(p) The finite volume discretisation however linearises this by representing one of the U terms in div(U*U) as the flux phi, hence ddt(U)+div(phi,U)Laplacian(nu,U)=grad(p) We then need to iterate around a bit to take account of the fact that when U changes from this solution, phi must be updated... Clear now? Gavin 

September 10, 2008, 08:52 
Thanks for the fast help.
Thi

#3 
Member
Joern Bader
Join Date: Mar 2009
Posts: 33
Rep Power: 9 
Thanks for the fast help.
This helps a lot. I didn't see the step: ddt(U)+U*div(U)Laplacian(nu,U)=grad(p) to ddt(U)+div(U*U)Laplacian(nu,U)=grad(p) Joern 

September 10, 2008, 09:24 
Here it is, with subscript x,y

#4 
Senior Member
Niels Gjoel Jacobsen
Join Date: Mar 2009
Location: Deltares, Delft, The Netherlands
Posts: 1,702
Rep Power: 27 
Here it is, with subscript x,y,z meaning differentiation and u,v,w being velocity components and U the vector:
In the xdirection div(U * U) reads: (u * u)_x + (u * v)_y + (u * w)_z = u_x u + u u_x + u_x u + u v_y + u_z w + u w_z = u_x u + u_x u + u_z w + u*(u_x + v_y + w_z) = u_x u + u_x u + u_z w where the term in the bracket are identical to zero for incompressible flows, as it is your continuity equation. The same can be done for the other directions and you will have understood the step above. Best regards, Niels
__________________
Please note that I do not use the Friendfeature, so do not be offended, if I do not accept a request. 

September 10, 2008, 10:29 
Thx for your Help.
I think

#5 
Member
Joern Bader
Join Date: Mar 2009
Posts: 33
Rep Power: 9 
Thx for your Help.
I think I now understand the solver algorithm. Now I have to understand the discretisation ;) Joern 

November 26, 2008, 18:26 
Hallo,
i have a new problem

#6 
Member
Joern Bader
Join Date: Mar 2009
Posts: 33
Rep Power: 9 
Hallo,
i have a new problem with the same topic I try to understand the sover sonicFoam. This solver solves the Equations: ddt(rho, U)+div(phi, U)laplacian(mu, U)=grad(p) and ddt(rho, e)+div(phi, e)laplacian(mu, e)=div(phi/rho)+mu*magSqr(symm(grad(U))) For me it looks like some kind of impulse and energy equation from the compressible Navier Stokes equations. Does someone know which equations sonicFoam solves or where i can find some literature about the algorithm an his mathematic roots? sorry for posting nearly the same question again, but i need the infos for my further work and i don't see it alone. thx, Joern 

November 27, 2008, 18:43 
sonicfoam is a solver for comp

#7 
New Member
Mark Michael
Join Date: Mar 2009
Location: Rostock, Germany
Posts: 5
Rep Power: 9 
sonicfoam is a solver for compressible ideal gas flow. That why the solver use the continuity,momentum, energy, and ideal gas equation in its algorithm.
look in the programmer's guide ! there is an nice tutorial named: "Supersonic flow over a forwardfacing step" on page 58 ! http://foam.sourceforge.net/doc/Guid...mmersGuide.pdf 

June 15, 2009, 13:44 

#8 
Member
Joern Bader
Join Date: Mar 2009
Posts: 33
Rep Power: 9 
I reactivate this old thread, cause i have a question about the sonicFoam solver.
sonicFoam is a solver with PISO loop for the compressible NavierStokes equations. I think i understand most of the solver but one think is not clear: if i set mu=0 in sonicFoam it solves the Euler Equations for a compressible, inviscid, perfect gas. (thats what i want to simulate) But there is a little difference. sonicFoam just looks at the inner energy e=T*Cv (just thermal energy). The Euler Equations (and also the NavierStokes) work with the energy e=T*Cv+1/2*mag(v)^2 (thermal energy + kinetic energy). why can the kinetic energy be ignored? And why is the the solver still consisten to the Euler/NavierStokes Equations? thx for help, Joern 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
IcoFoam  aap  OpenFOAM Running, Solving & CFD  15  May 28, 2012 08:30 
Density in icoFoam Densidad en icoFoam  manuel  OpenFOAM Running, Solving & CFD  8  September 22, 2010 04:10 
About phi in icoFoam  kar  OpenFOAM Running, Solving & CFD  3  February 20, 2008 06:20 
Possible bug in icoFoam  msrinath80  OpenFOAM Bugs  6  November 19, 2007 18:35 
IcoFoam on AIX 53  ds2taieb  OpenFOAM Installation  1  March 24, 2006 04:22 