periodic boundary conditions

[Frank Muldoon]

Hello all,

From the documentation it seems that PyFR itself does not itself create
periodic boundary conditions (i.e. define the required connectivity) and
hence such must be specified already in the mesh file.

In this regards, could folks mention how they create such boundary
conditions? I have am currently using Gmsh for PyFY meshes, but its
support for periodic boundaries is extremely poor.

Cheers,
Frank

--
Frank Herbert Muldoon, Ph.D. Mechanical Engineering
New Technologies and Service
27 Gzhatskaya street, room 205
Saint Petersburg
Russia, 195220
+79313075021 (cell)

Фрэнк Херберт Малдун, к.ф.-м.н.
Новые Технологии и Сервис
195220 г. Санкт-Петербург
ул. Гжатская, д. 27, комната 205
+79313075021 (мобильный)

fmuldoo (skype)
http://tetra.fluid.tuwien.ac.at/fmuldoo/public_html/webpage/frank-muldoon.html

[Zach Davis]

Hi Frank,

I’m not sure whether Peter and his team have a solution for you on the solver side, but I’ll mention that we have worked with his team to provide native PyFR support on the meshing front in Pointwise.  Creating periodic boundaries in Pointwise is much more straightforward and user-friendly.  The software also supports exporting meshes created in Gmsh or PyFR’s native grid formats.  If this is something that you may be interested in exploring, then feel free to contact me.

Best Regards,

Zach Davis Pointwise®, Inc. Sr. Engineer, Sales & Marketing 213 South Jennings Avenue Fort Worth, TX 76104-1107 E: zach....@pointwise.com P: (817) 377-2807 x1202 F: (817) 377-2799

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[arvind iyer]

Hi Frank,

You are right that in  PyFR, 'periodic' is not a boundary condition, like in many other CFD software. Periodicity is achieved at the stage of importing the mesh while setting up the connectivity between elements. 

PyFR does not directly use the periodic information in gmsh msh file.

Rather, while importing the mesh, it matches the locations of surface elements on the surfaces which are named in pairs

"periodic_n_l" with "periodic_n_r" n= 0,1,2 ... and makes them as periodic.

So if you want to make a periodic mesh for a rectangular channel, for instance, you would name:

min-x plane "periodic_0_l" and 

max-x plane "periodic_0_r", and likewise 

min-z plane "periodic_1_l" and 

max-z plane "periodic_1_r"

I do not think it matters which is _l and which is _r.

The catch here is,

• the mesh on the _l and the _r must conform with a single displacement.
  
• the displacement, if I remember it right, must me along x or y or z-axis (not rotating, not skewed).

When you make mesh with gmsh with extrusion of a surface wuth 'layers', the mesh is  automatically conforming on the end surfaces of the extrusion, even if the surface has an unstructured mesh. So, you can apply periodicity on those surfaces.

However, on a fully unstructured mesh, you would need to tell gmsh explicitly to set up identical mesh on the periodic surfaces. This is done by setting the appropriate flags in gmsh: http://gmsh.info/doc/texinfo/gmsh.html#Miscellaneous-mesh-commands 

Yes it is painful to do in gmsh.

You will find the euler vortex (structured) and the couette flow(unstructured) examples both using periodic surfaces

Hope the above answers your question.

Regards

Arvind

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================================
Dr. Iyer Arvind Sundaram

The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself.

Therefore all progress depends on the unreasonable man

- George Bernard Shaw.