[nepomnyi]

Hello dear CFDonline community.


I'm trying to decipher line 109 in interfaceProperties.C file in OpenFOAM8.



Here's the line itself:

// Cell gradient of alpha
     const volVectorField gradAlpha(fvc::grad(alpha1_, "nHat"));

I have managed to interpret everything in that line except for

"nHat"

.


Since it's taken in quotation marks, I conclude this is a variable of the string type. I couldn't find this variable anywhere in the interfaceProperties.C file or interfaceProperties.H file, therefore I went to the definition file of fvc::grad() function which is called fvcGrad.C (the function is defined on lines 68-80 in the file).



The function takes 3 arguments:

const tmp<GeometricField<Type

,

fvsPatchField

and

surfaceMesh>>& tssf

The first thing I don't understand is why we supply only 2 arguments to the function whereas, by its definition, it requires 3 arguments.



The second thing I don't understand is what these 3 arguments are and which one corresponds to "nHat".


Thank you in advance.
Ivan

[überschwupper]

I believe here is a strong misunderstanding. I would highly recommend to you, to take a C++ Tutorial.

The function you quoted is:

template<class Type>
 tmp<GeometricField<typename outerProduct<vector,Type>::type, fvPatchField,volMesh>> grad
 (
  const tmp<GeometricField<Type, fvsPatchField, surfaceMesh>>& tssf
 )
 {
  typedef typename outerProduct<vector, Type>::type GradType;
  tmp<GeometricField<GradType, fvPatchField, volMesh>> Grad
  (
  fvc::grad(tssf())
  );
  tssf.clear();
  return Grad;
 }

This function is templated. This is done because otherwise it would be necessary to tell the compiler each type of that function that we need (=a lot of overloaded functions, less readable, less flexible). The function only needs 1 argument of type "const tmp<GeometricField<Type, fvsPatchField, surfaceMesh>>& tssf", the template here is of type "class Type" -> you can substitute Type by vector, scalar or whatever is possible.