[victor13165]

Hello everyone,

I am running a simulation using sedFoam for sediment transport applications, which is modified from the twoPhaseEulerFoam solver.

Case description

I won't get into much details about the geometry etc since it is not relevant for my problem. In a nutshell, my inlet velocity profile is given with codedFixedValue to implement a log-law velocity profile. The solid (sediment) phase, named alpha_a, has similar codedFixedValue boundary conditions to set the sediment concentration throughout the domain.

Initially, alpha_a has the following distribution all over the domain (excerpt of my 0/alpha_a file) :

forAll(Cf, faceI)
            {
                 field[faceI] = 0.6128*0.5
                               *(1.0+tanh((2-Cf[faceI].y())*5000))
                               +1e-100;
}

Which gives an initial distribution as shown on the following picture
initial_alpha_a_distribution.png

Now, what I would like to do, is to set a higher alpha_a value at the inlet boundary, kind of like "injecting" a higher concentration at the inlet and seeing how it transports in the domain. Consequently, I changed my 0/alpha_a file to :

forAll(Cf, faceI)
            {
                 field[faceI] = 0.6128*0.5
                               *(1.0+tanh((2-Cf[faceI].y())*5000))
                               +1e-100;


                 if ( Cf[faceI].y() >= 2.0 ) 
                 {
                        field[faceI] += 0.05;
                 }
           }

Which just sets alpha_a=0.5 above y=2. Note that y=2 corresponds to the interface between the solid (sediment) and fluid (water) phases (see previous picture)


Issue description

The issue is, the value alpha_a=0.05 on the inlet boudary works fine, but alpha_a is not transported into the domain (see following picture)
zoom.png

As you can see on this picture, alpha_a is set to 0.05 on the boundary.

What I have tried so far

Instead of codedFixedValue, if I set my velocity profile as a fixedValue of (0.5 0 0) for example, alpha_a is properly transported throughout the domain exactly as I wanted. So I would think the issue comes from the codedFixedValue boundary condition for the velocity profile.

EDIT: Using GroovyBC to set the log velocity profile transports alpha_a properly, and solves my problem. I still keep this thread open because I'd love to get an explanation on why codedFixedValue doesn't work.

This is what the codedFixedValue for the velocity profile looks like:

inlet
    {
        type            codedFixedValue;
        value           uniform (0 0 0);

        name    inlet;

        codeInclude
        #{
            #include "fvCFD.H"
        #};

        codeOptions
        #{
            -I$(LIB_SRC)/finiteVolume/lnInclude \
            -I$(LIB_SRC)/meshTools/lnInclude
        #};
        codeLibs
        #{
            -lfiniteVolume \
            -lmeshTools
        #};
        code
        #{
            const fvPatch& boundaryPatch = patch();
            const vectorField& Cf = boundaryPatch.Cf();
            vectorField& field = *this;
            scalar t = this->db().time().value();
            forAll(Cf, faceI)
             {
       

                if (Cf[faceI].y() > 2) 
               {
                  if (t <= 4.0)
                   {
                     // Linearly increasing velocity magnitude under t=4s
                      field[faceI] = (0.1 + 0.9*(t/4.0))
                                     *vector
                                      (
                                         0.04318/0.41
                                         *log(30*(Cf[faceI].y()-2)
                                              /9e-4),
                                         0,
                                         0
                                       );
                  }
                  else
                   {
                     //This is the original velocity profile
                      field[faceI] = vector
                                    (
                                       0.04318/0.41
                                       *log(30*(Cf[faceI].y()-2) /9e-4),
                                       0,
                                       0
                                    );
                  }
               }
                else
                {
                  //velocity is 0 under y=2 which is the sediment bed
                   field[faceI] = vector(0,0,0);
               }
            }
        #};
    }

Question

Why does codedFixedValue not transport the alpha_a field? Clearly, setting a velocity fixedValue at the inlet works fine, so what did I miss?


I have attached my 0/alpha_a and 0/Ua files in case anybody wants to have a closer look. If you need more files/details, please let me know - I'm happy to provide any additional information.


Cheers and thanks in advance for any help.

alpha_a.txtUa.txt