[Gmsh] Create a Boundary Layer around a blade

jawisr at gmail.com jawisr at gmail.com
Fri May 15 10:48:48 CEST 2015

```Hi Alexander,
I know it has been a while since your last answer, but I have to try.
I need to create a boundary layer arround a wing imported in STEP. I try
with Boundary Layer Field but I can't make it work. Could you make your
boundary layer? Can you explain to me how this field works? A general
explanation of size fields would be really helpful.
I attach my code so you can take a look.

Please take into account that my wing is shaped by surfaces 5 and 6
(intrados and extrados). Since I want to run a 2D case the wing is placed
between two planes.

//Boundary Layer
Field[2] = BoundaryLayer;
Field[2].hfar = 1;
Field[2].hwall_n = 1;
Field[2].hwall_t = 2;
Field[2].thickness = 10;
Field[2].FacesList = {5, 6};
Field[2].AnisoMax = 1000000;
Field[2].IntersectMetrics = 1;
Background Field = 2;

I don't even know how big must be hwall and hfar parameters. If my chord is
1000 mm, how large should these parameters be if I want a 10 mm BL? I know
boundary layer depends on y+, I just want to know if these parameters are
mm, m or some kind of ratio.
And finally I'd like to know how "Background Field" works. If I set my
Boundary Layer field [2] as background, the whole mesh is refined with the
same size (tetra). If I set another field as background, the boundary layer
field is not noticed.

Thank you very much and I hope you can help me,

El domingo, 9 de febrero de 2014, 15:04:26 (UTC+1), Alexander Tismer
escribió:
>
> Dear Christophe,
>
> many thanks for your help.
>
> If I try to create the layer by extrusion I get an error:
>
> "Impossible to extrude entity 8 (of type 306)"
>
> As I mentioned in the first post I create my geometry using my own-written
> subclasses of GFace, GVertex and GEdge.
> Is it necessary to code the extrusion-function for my own geometry entity
> types?
>
> After spending some hours to the gmsh code and to the manual I figured out
> another way. I used a BoundaryLayer field.
>
> Field[1] = BoundaryLayer;
> Field[1].FacesList = {1,3,8,9};
> Field[1].hfar = .5;
> Field[1].hwall_n = .5;
> Field[1].hwall_t = .5;
> Field[1].thickness = 10.;
> Field[1].ratio = 1.1;
> Field[1].IntersectMetrics = 1;
> BoundaryLayer Field = 1;
>
> Using the mentioned field I get a mesh with a boundary layer. The mesh
> looks nice, but if I convert it by using "gmshToFoam" and check it with
> "checkMesh" I get some errors. The mesh fails the open boundary check.
>
> ***Boundary openness (-0.00152301 -0.000276836 -0.00087618) possible hole
> in boundary description.
>  ***Open cells found, max cell openness: 1, number of open cells 21
>
> The boundary layer looks very fine. Please find attached two pictures.
>
> If I don't create a boundary layer then my mesh is ok (according to
> checkMesh). But openfoam runs into problems with the periodic patches
> (cyclicAMI). I figured out that it is possible to set a master surface to a
> surface and gmsh copies the mesh from the master surface. I try to do that
> with my own function:
>
> void gmshVolume::setPeriodicPairOfFaces( GModel *gm, int const
> numFaceMaster, std::vector<int> const & EdgeListMaster,int const
> numFaceSlave, std::vector<int> const & EdgeListSlave) const {
>
> int NEdges=EdgeListMaster.size();
> GFace *gf = gm->getFaceByTag(abs(numFaceSlave));
> gf->setMeshMaster(numFaceMaster);
>         for (int i = 0; i < NEdges; i++){
>                 gf->edgeCounterparts[EdgeListSlave[i]] =
> EdgeListMaster[i];
>                 GEdge *ges = gm->getEdgeByTag(abs(EdgeListSlave[i]));
>                 ges->setMeshMaster(EdgeListMaster[i]);
>         }
> }
>
> Gmsh tries to mesh but ends with
>
> Error   : Only rotations or translations can be currently taken into
> account for periodic faces: face 2 not meshed
>
> Isn't it enough to set the master edges to edgeCounterparts on the slave
> surface? Because I'm sure that my two surfaces are axially symmetric.
>
> Thanks
> Alex
>
>
>
>
>
> -----Ursprüngliche Nachricht-----
> Von: Christophe Geuzaine [mailto:cgeu... at ulg.ac.be <javascript:>]
> Gesendet: Freitag, 7. Februar 2014 19:12
> An: Alexander Tismer
> Cc: gm... at geuz.org <javascript:>
> Betreff: Re: [Gmsh] Create a Boundary Layer around a blade
>
>
> On 07 Feb 2014, at 19:10, Christophe Geuzaine <cgeu... at ulg.ac.be
> <javascript:>> wrote:
>
> >
> > On 06 Feb 2014, at 10:05, Alexander Tismer <
> alexande... at ihs.uni-stuttgart.de <javascript:>> wrote:
> >
> >> Hello,
> >>
> >> I try to create a boundary layer around a blade of a hydraulic turbine
> with gmsh.
> >>
> >> According to the paper “Gmsh: a three-dimensional ﬁnite element mesh
> generator with built-in pre- and post-processing facilities” (page 18-19)
> gmsh is able to create such a layer from a set of source surfaces. For me
> it is not really clear how to do it.
> >> Has anybody an example geo file?
> >> Furthermore I want to do that with my own written subclasses of GEdge,
> GFace and GVertex using gmsh as a library. Is this also possible? Currently
> I created a 3-d mesh of my channel using my own written classes
> successfully. However I’m in trouble with the boundary layer creation
> around the blade, hub and shroud.
> >>
> >
> > Dear Alexander,
> >
> > The feature mentioned in the paper can be accessed by simply using the
> "Extrude" command (see the attached example).
>
> With the attachment:
>
>
> > This creates actual geometrical entities for the layer. A more
> "classical" boundary layer mesh generator (which does not create new
> entities, but simply extrudes a layer inside the volume) is also under
> development, but it's not documented yet.
> >
> > Christophe
> >
> >> Any help is really appreciated.
> >>
> >> Many Thanks
> >> Alex
> >> _______________________________________________
> >> gmsh mailing list
> >> gm... at geuz.org <javascript:>
> >> http://www.geuz.org/mailman/listinfo/gmsh
> >
> > --
> > Prof. Christophe Geuzaine
> > University of Liege, Electrical Engineering and Computer Science
> > http://www.montefiore.ulg.ac.be/~geuzaine
> >
> >
> >
>
> --
> Prof. Christophe Geuzaine
> University of Liege, Electrical Engineering and Computer Science
> http://www.montefiore.ulg.ac.be/~geuzaine
>
>
>
>
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