[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].Quads = 0;
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].Quads = 0; 
> 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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