It was a bit funny from my end. Averaging is not a good option. I guess only the exact value of alpha times the flow discharge at the outlet boundary face can give accurate value. Any idea of how do i get the alpha value at the boundary cell?

Hi Saideep,

I am not sure if I understood correctly your question. Anyway you can use swak4Foam to calculate the average of alpha over a surface (e.g. outlet):

{

type                                 swakExpression;

valueType                       patch;

patchName                     outlet;

accumulations                (average);

outputControlMode         timeStep;

outputInterval                  1;

aliases                             {

                                           alphaWater alpha.water;

                                        }

expression                       "sum(alphaWater*area())/sum(area())";

verbose                             true;

}

I hope this helps.

I'm using this for water flux at the outlet boundary:

waterFrOutlet

{

type swakExpression;

valueType patch;

patchName outlet;

aliases {water alpha.water;}

expression "phi*water";

accumulations ( sum );

outputControlMode timeStep;

outputInterval 1;

verbose false;

}