# rotating mesh with cyclic boundaries

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November 16, 2013, 13:53
rotating mesh with cyclic boundaries
#1
New Member

Christian
Join Date: Nov 2013
Posts: 7
Rep Power: 3
Hello everybody,

first of all i have to admit, that this is my first bigger project with OpenFoam. I wish to simulate a radial compressor stage using rhoPimpleDyMFoam. In order to get a quick solution i would like to use cyclic patches and rotate the whole mesh with a constant rotational speed between an inlet- and outlet-mesh. So, my question is simple : Is it possible to use cyclic patches instead of meshing the whole stage in this case?
For example: would it be possible to change the tutorial " annularThermalMixer " that way, so that there is just one single blade and a piece of the outer mesh?
I would be very happy, if someone could help me with this question. I already read some stuff about GGI and dynamic Meshes, but until now i didnt found a solution

Thanks for support.
Attached Files
 rotating_system.pdf (93.9 KB, 33 views)

 November 19, 2013, 07:00 fixed Wall #2 New Member   Christian Join Date: Nov 2013 Posts: 7 Rep Power: 3 OK, I solved the problem by editing an "dynamicMeshDict" -file.Now my mesh rotates, as it should . But now I have a new problem: the upper wall have to stand still. I think that would be no problem, if there is a big gap between the shovel and the channel-wall (like in the annularThermalMixer-case), but in this case the gap is around 0,5 mm thin. So there are just a few number of cells in it. I dont exactly now how the tutorial "annularThermalMixer" work, but in my oppinion it would be the simplest way to do it similar. But I have a little doubt of it, because its so near to the wall and may disturb the solution of the boundary-layer. Does anybody now a more simple way???Is it possible for example to write a boundarycondition in the manner U_w=-Omega*R(z), where the velocity at the wall is negative to the direction of the rotation but not constant in place? Thanks for help and best regards!

 November 20, 2013, 04:12 #3 New Member   Thomas Reviol Join Date: Jul 2011 Location: Germany, Kaiserslautern Posts: 25 Rep Power: 5 Hi Chrisitan, you could choose the BC "rotatingWallVelocity". Regards Thomas

 November 26, 2013, 08:51 thx #4 New Member   Christian Join Date: Nov 2013 Posts: 7 Rep Power: 3 Hi Thomas! Thank you very much for your reply! Wouldnt be me, if there would be no more question at this point : Is rotatingWallVelocity-BC at the Rotor on static mesh the same like a moving mesh with uniformValue (0 0 0) -BC on the Rotor? Best Regards, Christian!

 November 26, 2013, 11:00 #5 New Member   Thomas Reviol Join Date: Jul 2011 Location: Germany, Kaiserslautern Posts: 25 Rep Power: 5 Hi Christian, for simulating moving mesh, I define the moving regions within the rotating mesh with the BC "movingWallVelocity" (value is set to uniform (0 0 0)). For rotating faces within the non-rotating mesh, I set the BC "rotatingWallVelocity". Regards Thomas

 November 27, 2013, 15:32 #6 New Member   Christian Join Date: Nov 2013 Posts: 7 Rep Power: 3 Haudi Thomas! Thanks for your answer! I have tried for innerwall AND blade (rotor) the following (non-moving mesh) for U: type rotatingWallVelocity; origin (0 0 0); omega 100; value uniform (0 0 0); and the outerwall type fixedValue; value uniform(0 0 0); The strange thing is, that, when I plot the solution, the velocity at the innerwall is , as expected not 0, but on the blade it is 0... how is that possible? there must be something wrong... Im also running the dynamic-mesh case, which seems to do a better job. I'll post my results as I get them. Best Regards, Christian.

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