[Ali_Sh]

I would like to specify a small section of a wall to be outlet. So, I have used codedFixedValue to specify some meshes which centers are within a considered circle on the wall. The code will not be difficult when the boundary condition would be specified by velocity only, not the flow rate. The model is as the following photo:
image.jpg
The inletWalls in the code is written only for showing how flow rate can be written for a patch. How to specify this boundary condition i.e. type flowRateOutletVelocity and its value in the outletWalls section?

/*--------------------------------*- C++ -*----------------------------------*\
  | =========                 |                                                 |
  | \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
  |  \\    /   O peration     | Version:  v3.0+                                 |
  |   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
  |    \\/     M anipulation  |                                                 |
  \*---------------------------------------------------------------------------*/
FoamFile
{
  version     2.0;
  format      ascii;
  class       volVectorField;
  object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 1 -1 0 0 0 0];

internalField   uniform (0 0 0);

boundaryField
{
  inletWalls
  {
    type                 flowRateInletVelocity;
    volumetricFlowRate   0.3;
    value                uniform (0 0 0);
  }
  outletWalls
  {
   	type            codedFixedValue;
    	value           uniform (0 0 0);
    	redirectType    perf_outlet;

	code
    	#{
            const fvPatch& boundaryPatch = patch(); 
            const vectorField& Cf = boundaryPatch.Cf(); 
            vectorField& field = *this; 
        
            const scalar perf_r = 0.12;          // radius of the circle

 	    	forAll(Cf, faceI)
            {
                if (
		   //(Cf[faceI].y() == 1.1) &&
                   (pow(Cf[faceI].x(),2) * pow(Cf[faceI].z(),2) <= pow(perf_r,2))     // when the circle is on Y-plane
                   )
            	   {
               		field[faceI] = vector(0,1,0);   // It must be modified for specifying flowrate
	           }
	    }
   	#};         

  	codeOptions
  	#{
       	    -I$(LIB_SRC)/finiteVolume/lnInclude \
       	    -I$(LIB_SRC)/meshTools/lnInclude
   	#};

  	codeInclude
   	#{
      	    #include "fvCFD.H"
      	    #include <cmath>
     	    #include <iostream>
	#};

  }
  fixedWalls
  {
    type            slip;
  }
}

// ************************************************************************* //

I would be grateful if someone would like to help me.