[jgross]

Hi everybody,

I am trying to use swakExpression to calculate a desired quantity on a faceZone. Before I begin creating the faceZone for the actual region of interest, I thought I would test out the utility on an already defined faceZone that is being already defined from a patch. Ultimately, I would create the faceZone at the desired location, but I thought it would be good to test this out first.

However, every time I run the case, there is a FOAM warning about it being an empty field:

Expression cavImpeller1 : --> FOAM Warning : 
    From function Field<T> *SubsetValueExpressionDriver::getFieldInternalAndInterpolate(const word &name,const Subset &sub)
    in file SubsetValueExpressionDriverI.H at line 264
    Going to interpolate p
--> FOAM Warning : 
    From function gAverage(const UList<Type>&)
    in file /home/jg847/foam/foam-extend-4.0/src/foam/lnInclude/FieldFunctions.C at line 541
    empty field, returning zero.
 average=0

I am certain that the faceZone is not empty as when I check the constant/polymesh/faceZones, the required zone contains 169 faces:

GGI_EXT_ZONE
{
    type faceZone;
    faceLabels      List<label> 
169

The swakExpression is:

    cavImpeller1
    {
      type swakExpression;
      valueType faceZone;
      zoneName GGI_EXT_ZONE;
      outputControl timeStep;
      outputControlMode timeStep;
      outputInterval 1;
      enabled true;
      autoInterpolate true;
      expression "sum(phi*2*(p+101-3.169))/sum(phi)";
      verbose true;
      allowCoupled true;
      accumulations ( average );
    }

The faceZone in question acts as a mixing plane interface, so I'm wondering if that is the cause of the issue, but I don't think it should affect the calculation as those quantities are still available for calculation.

Anyone have any ideas as to why this might be the case?

James

[JulioPieri]

I know this is an old thread, but just to help future foammers:

To write for a faceZone, you need to declare a "variables" entry before, where you specify the variable name with "{faceZone'facezonename}" indicating the faceZone. The syntax is something like this:

cavImpeller1
    {
      type swakExpression;
      valueType faceZone;
      zoneName GGI_EXT_ZONE;
      outputControl timeStep;
      outputControlMode timeStep;
      outputInterval 1;
      enabled true;
      autoInterpolate true;
      variables "dummyVariable{faceZone'zone_name}=sum(phi*2*(p+101-3.169))/sum(phi);"
      expression "dummyVariable";
      verbose true;
      allowCoupled true;
      accumulations ( average );
    }