[kcn]

Hello,

I am developing a solver for temperature transport in a region where some places have porous structure. I need to solve a different transport equation in porous regions and another in ordinary regions. I plan to do this using an if condition as indicated below.

if (porosity == 1)
{ solve Equation A;}
else
{solve Equation B;}

I have defined porosity as a geometricField.

When I try to compile the code it does not recognize the condition " porosity == 1"

Can someone please tell me how to include the value of a geometricField in an if condition in OpenFOAM.

[jhoepken]

Hi,

if you do that, you have to check in each cell and this in turn involves a manual loop over all cells. This is slow as hell. Or even slower.

Why don't you use a blending field, which is 1 where equation 1 should be solved and 0 where equation 2 should be solved. This blending field - basically like the VoF rule of mixture approach - is then multiplied with the particular equations.

Otherwise, as I said, you have to loop over all cells and check locally using

forAll(porosity, pI)
{
    if(porosity[pI] == 1)
....
}

[kcn]

Dear jhoepken,

Thanks a lot for your help. I'm bit new to openfoam. Can you please explain a little bit about using a blending field for this purpose. Actually, its the first time I heard about it. Are there any built in solvers that uses blending fields so that I can have a look at code?

Thanks
kcn

[kcn]

Dear jhoepken,

I managed to solve the problem using your idea. I used a scalarfield of 1 and 0 as you said and multiplied some terms in my equations with that field. Now it easily calculates using different equations in different zones.

I also tried the for loop method using the code you provided. As you said it took a long time to run even in a coarse mesh.

Thanks a really lot.

kcn

[jhoepken]

Hi kcn,

great that you've figured it out. As a general rule of thumb, you should avoid looping over cells and accessing field values wherever possible.