# [snappyHexMesh] wingMotion Tutorial

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 October 24, 2010, 21:42 wingMotion Tutorial #1 Senior Member   Daniel Join Date: Jul 2009 Location: Montreal, Canada Posts: 156 Rep Power: 15 Hello everyone, I am new at snappyHexMesh, and I am trying to use the program to generate a 2-D mesh of an airfoil. I have been following the wingMotion series of tutorials, but the problem I run into is that I must avoid extruding a projection of the mesh as is done in wingMotion2D_simpleFoam. The reason is that I have modified the geometry (wing_5degrees.obj) file to include a second patch for a flap, which would be lost in the extrusion since autoPatch requires a geometrical feature to separate two patches - no such feature is present, I have merely set the trailing 20% of the airfoil as a flap. When snappy is run, it generates a 3D mesh about 50 cells deep on the z-axis, for the wing (and flap) patch(es). Why does snappy choose this number, and how can it be reduced? I tried making the geometry thinner, but that did not make a difference. Is is possible to extrude while maintaining the patches in the axis along which the extrusion is taking place? Thanks in advance, Dan

October 27, 2010, 03:20
#2
Senior Member

Ivan Flaminio Cozza
Join Date: Mar 2009
Location: Torino, Piemonte, Italia
Posts: 209
Rep Power: 17
Hi Daniel,

I'm working too in 2D (or extruded) meshing with SHM, in my opinion it is the best choice for cylindrical bodies (I mean, bodies that are "geometrically" extruded in the third direction, like a unswept wing). If I understood, SHM put many cells in z dir. as the refining procedure is just splitting the cells like this:

if I have one exa and I want to reach the next level of refinement, divide by two ALL the edges of the exa, and the result is 4 new exas.

So, up to now SHM meshes are inerently 3D, if you want it 2D you have to do something, like extruding!

Quote:
 Originally Posted by dancfd Hello everyone, I am new at snappyHexMesh, and I am trying to use the program to generate a 2-D mesh of an airfoil. I have been following the wingMotion series of tutorials, but the problem I run into is that I must avoid extruding a projection of the mesh as is done in wingMotion2D_simpleFoam. The reason is that I have modified the geometry (wing_5degrees.obj) file to include a second patch for a flap, which would be lost in the extrusion since autoPatch requires a geometrical feature to separate two patches - no such feature is present, I have merely set the trailing 20% of the airfoil as a flap. When snappy is run, it generates a 3D mesh about 50 cells deep on the z-axis, for the wing (and flap) patch(es). Why does snappy choose this number, and how can it be reduced? I tried making the geometry thinner, but that did not make a difference. Is is possible to extrude while maintaining the patches in the axis along which the extrusion is taking place? Thanks in advance, Dan

 October 27, 2010, 16:26 #3 Senior Member   Daniel Join Date: Jul 2009 Location: Montreal, Canada Posts: 156 Rep Power: 15 Hi Ivan, Thanks for the response. I understand the inherent 3-D nature of sHM, and that extruding will make it 2-D, however I cannot extrude the mesh without losing my patch. Thanks again, Dan

 November 13, 2016, 10:12 help with the boundary conditions #4 Member   Vignesh Rajendiran Join Date: Aug 2016 Location: Chennai, India Posts: 60 Rep Power: 8 Hello, I am somewhat new to openfoam. And I am trying to simulate the flow around an airfoil for my assignment. I was using the wingmotion2D test case as a base for my problem. But I found some difficulties with giving my boundary conditions and giving the reference area value for the airfoil. If you were able to solve it, I want to know how you gave your boundary conditions and the reference area in controldict. Please help me out. Thank you Viki