[VVN]

Hello All,

I want to calculate drag coefficient at each time step on front face of each obstacle (here 6 buildings). Here is my blockMesh file

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  7
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

convertToMeters 1;

vertices
(
    (0 0 0)
    (200 0 0)
    (200 150 0)
    (0 150 0)
    (0 0 250)
    (200 0 250)
    (200 150 250)
    (0 150 250)
);

blocks
(
    hex (0 1 2 3 4 5 6 7) (50 50 50) simpleGrading (1 1 1)
);

edges
(
);

boundary
(
    atmosphere
    {
        type patch;
        faces
        (
            (4 5 6 7)
        );
    }
    bottom
    {
        type wall;
        faces
        (
            (0 3 2 1)
        );
    }
    left
    {
        type cyclic;
        neighbourPatch    right;
        faces
        (
            (0 4 7 3)
        );
    }
    right
    {
        type cyclic;
        neighbourPatch    left;
        faces
        (
            (2 6 5 1)
        );
    }
    entry
    {
        type wall;
        faces
        (
            (1 5 4 0)
        );
    }
    exit
    {
        type patch;
        faces
        (
            
            (3 7 6 2)
        );
    }
    building
    {
        type wall;
        faces
        (
        );
    }
);

mergePatchPairs
(
);

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

I am able to remove solid domain (buildings) using toposet. Here is toposet file -

 /*--------------------------------*- C++ -*----------------------------------*\
    =========                 |
    \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
     \\    /   O peration     | Website:  https://openfoam.org
      \\  /    A nd           | Version:  7
       \\/     M anipulation  |
  \*---------------------------------------------------------------------------*/
  FoamFile
  {
      version     2.0;
      format      ascii;
      class       dictionary;
      object      topoSetDict;
  }
  
  // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
  
  actions
  (
      {
          name    c0;
          type    cellSet;
          action  clear;
      }
      {
          name    c0;
          type    cellSet;
          action  invert;
      }
 
      {
          name    c0;
          type    cellSet;
          action  delete;
          source  boxToCell;
          sourceInfo
          {
          boxes
          (			( 35 50 0 ) ( 65 70 80 )
 			( 85 50 0 ) ( 115 70 80 )
 			( 135 50 0 ) ( 165 70 80 )
 			( 35 100 0 ) ( 65 120 80 )
 			( 85 100 0 ) ( 115 120 80 )
 			( 135 100 0 ) ( 165 120 80 )
         );
         }
     }
     
);

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

But could you please tell me how to proceed further? I have simulated the results and now want to extract drag coefficient.

To try out, I added forcecoeff function in controldict file.

functions
{
forceCoeffs1
{
    // Mandatory entries
    type            forceCoeffs;
    libs            ("libforces.so");
    patches         (building);


    // Optional entries

    // Field names
    p               p;
    U               U;
    rho             rho;
    rho         rhoInf;
    rhoInf      1000;

    // Reference pressure [Pa]
    pRef            0;

    // Include porosity effects?
    porosity        no;

    // Store and write volume field representations of forces and moments
    writeFields     yes;

    // Centre of rotation for moment calculations
    CofR            (0 0 0);

    // Lift direction
    liftDir         (0 0 1);

    // Drag direction
    dragDir         (0 1 0);

    // Pitch axis
    pitchAxis       (1 0 0);

    // Freestream velocity magnitude [m/s]
    magUInf         30;

    // Reference length [m]
    lRef            80;

    // Reference area [m2]
    Aref            2400;

    // Spatial data binning
    // - extents given by the bounds of the input geometry
    binData
    {
        nBin        20;
        direction   (0 1 0);
        cumulative  yes;
    }
}
}

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

But here for patching I used 'building' patch which contains all my 6 buildings and this gives wrong results. I want to have drag coefficient for each building. So I will be require to have 6 different patches, if I am correct.

Could anyone tell me how can I create patch for front face of each building which was deleted from topoSet? How can I use createPatch here? And if anyone has different approach, let me know.

Thank you in advance : )