# Applying a retarding shear in a row of cells for incompressible flows

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 November 20, 2023, 03:56 Applying a retarding shear in a row of cells for incompressible flows #1 Member   Marķa Rosales Join Date: Mar 2023 Location: Spain Posts: 37 Rep Power: 3 Hello community, Can you please give me your opinion in this implementation of 'retarding shear stress' proposed by Richard & Hoxey (1993) in the row of cells adyacent to wall that helps to minimize the over production of TKE and so the peak of TKE when plotting against vertical profile: shear = rho * (u_friction)² I'm running simpleFoam, must I remove or keep rho (density) in the calculation of the source? By using topoSetDict we can catch the first row of cells adyacent to ground patch (wall): first patchToFace and then setToCellZone. Then, by using fvOptions codedVectorSource: PHP Code: ``` retardingShear{    type            vectorCodedSource;    selectionMode   cellZone;    cellZone        areaSet;  // name of my cellZone    fields          (U);    writeToFile     true;    name            retardingShear;        codeCorrect        #{        #};    codeConstrain    #{    #};        codeInclude        #{        #};    codeAddSup            #{                vectorField& retardingShear = eqn.source();  // will asign calculation to source side of fvMatrix         vector Ufriction (-0.57 0 0); // is the friction velocity near wall         vector diskRetardingShear (-1 0 0); // is the direction opposite to normal wind flow                const labelList& cellIDs = cells();                forAll(cellIDs, i)                {                    label cellI = cellIDs[i];                            retardingShear[cellI] += mag(Ufriction)*diskRetardingShear; // the left side with += is thought to be 'a sink', AND the right side is the value of shear with its current direction                }}  ``` Is it good practice to combine '+=' (sink assigment) with the current direction of this retarding shear ? I've seen that some user multiplies the sources term by cell volumes, when is this needed? I apologize but I lost the original code and this code is what I remember that I could run. Any ideas are welcome Last edited by MMRC; November 20, 2023 at 05:13.

 November 22, 2023, 10:28 #2 Member   Marķa Rosales Join Date: Mar 2023 Location: Spain Posts: 37 Rep Power: 3 Hello community, Here is my code, in fact, it helped to lower the effect of over production of TKE codedSource { type vectorCodedSource; selectionMode cellSet; cellSet groundCellSet; fields (U); name retardingshear; codeInclude #{ #}; codeCorrect #{ #}; codeAddSup #{ vectorField& Usource = eqn.source(); const scalarField& V = mesh_.V(); vector dir(-1,0,0); // Apply the source forAll(V, i) { // cell volume specific source Usource[i] -= (0.1*V[i])*dir; }; #}; codeConstrain #{ #}; } The value I used was thinking that I should have input of it without density , because I'll be using density. The use of volume of the cell is something that I copy someone used for their sources on other fields, maybe this is not correct. Please share your comments, this supposed to be a 'retarding shear stress' applied to the cell adjacent to ground patch

 Tags fvoption, shear stress, sources

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