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Channel Flow with Constant Mass Flow Rate

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Old   August 1, 2018, 10:31
Default Channel Flow with Constant Mass Flow Rate
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I am trying to simulate a channel flow of infinite stream-wise length, fixing a constant mass flow rate across the channel to drive the flow. I am using simpleFoam with kw SST turbulence model. My strategy is to set a periodic boundary condition at the inlet and outlet for U, nut, k and w (to give the effect of an infinite stream-wise length) and allow the pressure to be solved (to ensure a fixed mass flow rate). I am using OF version 1.7.1.

I tried to set a cyclic boundary condition for the inlet and outlet in the blockmesh dictionary file, however this meant that the simulation would not run unless I set the inlet/outlet boundary condition for every flow variable as cyclic in the field files (I do not want to do this for pressure).

Following this, my approach was to use the mappedPatch in the blockmesh dictionary file as follows:

Code:
boundary
(
       inlet
       {
                type                    mappedPatch;
                sampleMode        nearestPatchFace;
                samplePatch        outlet;
                faces                   ((7 4 0 3));
        }
 
        outlet
        {
                 type                    patch;
                 faces                   ((2 1 5 6));
The field files for all the variables are as follows:

U:

Code:
boundaryField
{
                 inlet
                 {
                       type                      mapped;
                       value                     uniform (10 0 0 );
                       setAverage             true;
                       average                 (10 0 0);
                  }

                 outlet
                 {
                       type                      zeroGradient;
                  }
p:

Code:
boundaryField
{
                 inlet
                 {
                       type                      zeroGradient;
                  }

                 outlet
                 {
                       type                      zeroGradient;
                  }
omega:

Code:
boundaryField
{
                 inlet
                 {
                       type                      mapped;
                       value                     uniform 200000;
                       setAverage             false;
                       average                 200000;
                  }

                 outlet
                 {
                       type                      zeroGradient;
                  }
k:

Code:
boundaryField
{
                 inlet
                 {
                       type                      mapped;
                       value                     uniform 0.002;
                       setAverage             false;
                       average                 0.002;
                  }

                 outlet
                 {
                       type                      zeroGradient;
                  }
nut:

Code:
boundaryField
{
                 inlet
                 {
                       type                      mapped;
                       value                     uniform 0;
                       setAverage             false;
                       average                 0;
                  }

                 outlet
                 {
                       type                      zeroGradient;
                  }
Reading other posts on the form I believe that the mappedPatch boundary type is the one to use along with mapped in the field files. I can generate blockMesh and decompose my domain without any issue, but when I mpirun my case with these conditions, I receive an error. So I need help with the following:

-Do these boundary conditions make sense for what I am trying to achieve?

-What is the function of "sampleMode" and "samplePatch" entries (sampleMode is required when using mappedPatch type)?

-I have read that the mass flow rate is fixed through setting "true" for the "setAverage" entry in the "U" field file. Is this correct?

Thanks
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boundary condition, channel, mapped, mass flow rate

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