# ??fvVectorMatrix+fvVectorField??

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

February 17, 2013, 17:52
??fvVectorMatrix+fvVectorField??
#1
New Member

Alexander
Join Date: Dec 2009
Location: Saint-Petersburg
Posts: 29
Rep Power: 9
Hello All!

I try to remake the icoFoam solver to an solver for stratified almost incompressible liquid and I've an following problem:

I added a new term to momentum equation, which is defined as: - rhoMin+f*(rhoMax-rhoMin)-rho0)/rho0*g
(where rhoMin, rhoMax, rho0 are a constants)

And if I write the momentum equation a intuitive way:

Quote:
 fvVectorMatrix UEqn ( fvm::ddt(U) + fvm::div(phi, U) - fvm::laplacian(nu, U) ); solve(UEqn == -fvc::grad(p)+ (rhoMin+f*(rhoMax-rhoMin)-rho0)/rho0*g ); dimensionedScalar ks=nu/1000; fvScalarMatrix SEqn ( fvm::ddt(f) + fvm::div(phi, f) - fvm::laplacian(ks, f) ); SEqn.solve();
Solver doesn't work well (velocity is induced, but scalar f isn't transfered)

But if we write the equation as follows

Quote:
 fvVectorMatrix UEqn ( fvm::ddt(U) + fvm::div(phi, U) - fvm::laplacian(nu, U) ///////////////////////////////////////////////////////////////////////////////// - rhoMin+f*(rhoMax-rhoMin)-rho0)/rho0*g //////////////////////////////////////////////////////////////////////////////// ); solve(UEqn == -fvc::grad(p));///////////////////////////////////////////////// dimensionedScalar ks=nu/1000; fvScalarMatrix SEqn ( fvm::ddt(f) + fvm::div(phi, f) - fvm::laplacian(ks, f) ); SEqn.solve();
Solver works normally!

And for me it's realy strange, because expression - fvm::laplacian(nu, U)- rhoMin+f*(rhoMax-rhoMin)-rho0)/rho0*g means that we add matrix coefficient to vector.

 February 18, 2013, 02:53 #2 Senior Member   Bernhard Join Date: Sep 2009 Location: Delft Posts: 790 Rep Power: 15 All of the terms are vectors, i.e. the Laplacian of a vector is a vector and your custom term is also a vector, since you include g. Is this what your confusion is about?

 February 18, 2013, 03:18 #3 Senior Member   Niels Gjoel Jacobsen Join Date: Mar 2009 Location: Deltares, Delft, The Netherlands Posts: 1,758 Rep Power: 29 Hi Alexander, I suppose that you question is about two "identical" modifications to the momentum equation, however, you get two different results on the flow field, correct? The second implementation is the correct one to choose, simply because you are otherwise solving a pressure equation, which do not know about the additional source term. When you put the source inside fvVectorMatrix, it works correctly with respect to the pressure-velocity coupling. Kind regards Niels sharonyue likes this.

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

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

 Contact Us - CFD Online - Privacy Statement - Top