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OpenLB – Open Source Lattice Boltzmann Code Forums on OpenLB General Topics SuperLatticePhysWallShearStress3D()

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    I have a small doubt regarding the Wall shear Stress 3D. It gives the norm value when we add a functor for it. I need components of the shear stress for each direction(X,Y,Z). In the forum below, there has been discussion about the same.

    I was not able to understand this line.
    Then you need to increase the functor dimension of both Super and BlockLatticePhysWallShearStress3D to 3 in order to have 3 output components.

    As I am new to C++, I could not understand how to increase the functor dimension and how to output each stress component.

    I would really appreciate help in this case.

    Thank you


    Dear sahilbhapkar30,

    thank you for your question.

    The functor dimension can be specified in line 50 and 77 of by modifying the last argument of the parent SuperLatticePhysF3D<T, DESCRIPTOR>(sLattice, converter, 1).



    Dear Stephan,

    Thank you for your response. I have another doubt.I want to calculate the wall shear stress at the inlet and outlet of my 3D geometry.

    I implemented this thing in the main:

    SuperLatticePhysWallShearStress3D<T,DESCRIPTOR> wss(sLattice, superGeometry, 3, converter, inflow1);
    SuperLatticePhysWallShearStress3D<T,DESCRIPTOR> wss1(sLattice, superGeometry, 3, converter, inflow2);
    SuperLatticePhysWallShearStress3D<T,DESCRIPTOR> wss2(sLattice, superGeometry, 4, converter, outflow_wall);
    SuperLatticePhysWallShearStress3D<T,DESCRIPTOR> wss3(sLattice, superGeometry, 4, converter, outflow_wall_2);

    where inflow1, inflow2, outflow_wall and outflow_wall_2 are the indicator cuboids which I have used for the inlet and outflow.

    In addition, I have implemented the functor (vtmWriter.addFunctor( wss)) for each of them in the get results.

    But after the simulation, I am getting the wall shear stress value for the inlet flow only. If I comment the inflow region area, I do get the outflow wall shear stress value if I rerun the simulation.

    Could you tell me, what I am doing wrong?

    Thank you.


    Hi sahilbhapkar30,

    that’s hard to tell right away.

    Please make sure not to specify things multiply.
    Ensure the correct material number and cuboid definitions, i.e. to hit the nodes correctly with the indicator cuboids (you can double-check by loading the ./tmp/vtkData/geometry_<>.vtm file into paraview and visualizing as points).

    Also, in the getResults function call all of them in a row:
    SuperLatticePhysWallShearStress3D<T,DESCRIPTOR> wss(…);
    SuperLatticePhysWallShearStress3D<T,DESCRIPTOR> wss1(…);
    SuperLatticePhysWallShearStress3D<T,DESCRIPTOR> wss2(…);
    SuperLatticePhysWallShearStress3D<T,DESCRIPTOR> wss3(…);
    vtmWriter.addFunctor( wss );
    vtmWriter.addFunctor( wss1 );
    vtmWriter.addFunctor( wss2 );
    vtmWriter.addFunctor( wss3 );

    Good luck with that!


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