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Carotid Simulation – no flow through one branch of bifurcation

OpenLB – Open Source Lattice Boltzmann Code Forums on OpenLB General Topics Carotid Simulation – no flow through one branch of bifurcation

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  • #8498
    Lauren E
    Participant

    Good morning,

    I have swapped the stl file on the aorta3d example for a bifurcating carotid stl but I am only getting flow through one of the branches. At this time I havent changed anything else except things related to the new stl.

    The branch I am getting flow through is cut in line with an axis, but the blocked one is not.
    I thought I had changed the IndicatorCircle3D information correctly to accommodate for this, but I get an unusual grill type pattern on the blocked outlet and no flow through – it looks like not all the points on this region have been allocated the right material number?

    IndicatorCircle3D<T> outflow1( -0.0029429384999999997, -0.00046020999999999996, 0.02223085, 0.316, 0., -0.948, 0.0043/2 );
    IndicatorCylinder3D<T> layerOutflow1( outflow1, 4.*converter.getConversionFactorLength() );
    superGeometry.rename( 2,5,1,layerOutflow1 );

    I have tried changing the 4. in front of *converter.getConversionFactorLength() but it doesnt seem to make any difference.

    How do I set up the outlet that is not in line with the axis to correct this issue? Or do I need to change the stl so both outlets are in line with the axis?

    Kind regards,
    Lauren E

    #8499
    Lauren E
    Participant

    Here is a link to a google drive folder that contains screen shots of the problem explained above.

    https://drive.google.com/drive/folders/1MvavEvxkVrr1x3y6KAQsomuvMV29fs28?usp=sharing

    One of the images shows how one outlet is complete and the other outlet is showing as lines.

    #8504
    Adrian
    Keymaster

    This is most likely caused by the outflow layer being non-axis aligned and “too thin”, causing the staircase approximation to only be realized partially. The geometry should be better if you increase the cylinder length (which you already tried) so the issue is probably that the wall of material 2 that the call renames is also incomplete.

    However, depending on the boundary condition (i.e. if you use the default pressure boundary) you will need to rotate the geometry s.t. the outlet is axis aligned anyway as pressure boundaries are tricky in such situations (one common approach is to flip velocity and pressure boundaries s.t. there is only a single pressure inlet and multiple (not necessarily axis-aligned) velocity outlets.

    #8510
    TSchenkel
    Participant

    Cheers Adrian, that answered the second part of the question we hadn’t asked yet: would the off-axis work for pressure BC as well? Since the off-axis, off-lattice BCs seem to be for wall and velocity only. If I understand you correctly, the answer is “No”.

    So our best approach would be to add an extension to the geometry and make it align with the lattice.

    Since we only have the velocity waveform for the inlet, the swap to pressure inlet and velocity outlet (like in the bifurcation3d example) is not an option in this case.

    With our geometry I think the geometry is such that an extension of the indicator cylinder would mean that the wall would not intersect with the extended cylinder (since the vessel opens up in places going inward from the outlet), as you suggested.

    So we’ll have to add the extensions to the geometry to accommodate for these limitations in the LBM BC definition and lattice orientation.

    Is there something like Bouzidi for pressure?

    • This reply was modified 3 weeks, 4 days ago by TSchenkel.
    #8592
    mathias
    Keymaster

    Q: Is there something like Bouzidi for pressure?
    A: No, there is not, sadly.

    You may send Shota or Fedor an email. They might have an idea or they are aware of a paper on that.

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