variable pitch vertical axis turbine mesh motion

bolus13 · October 29, 2016, 15:48

Hi All,

I am modelling a variable pitch vertical axis turbine in a channel in cfx.

The model is setup in such a way that the turbine and the blades can both be modelled in circular rotating domains. This works well with moving meshes in cfx. See attach image for an impression.

The downside of the current moving mesh is that the turbine diameter can not be increased beyond the current size, otherwise the circular domains will intersect with the wall. This does not seem to work.

Would anyone know how to alter the mesh model, such that a larger diameter turbine can be modelled inside the channel where the blades move closer to the wall.

may thanks

ghorrocks · October 30, 2016, 17:35

You can edit meshes in ICEM and many other meshing software (GridGen etc).

But it is usually much better to go back to the original geometry, fix the geometry and remesh. This is usually much easier than editting and existing mesh.

bolus13 · October 31, 2016, 03:39

So, in a transient run I would change the geometry and remesh at each time step?

That sounds logical to me. Do you know if this something that can be done in workbench? This is what is generally work with.

ghorrocks · October 31, 2016, 05:18

I may have misunderstood your question. I assumed you were talking about changing an existing mesh for a new geometry. You seem to be talking about dynamic remeshing during a run.

Can you explain what you are trying to model and what the motion you expect is? Also, where does the motion come from?

bolus13 · November 1, 2016, 03:51

I am modelling a vertical axis turbine inside a channel. The flow is driven by a pressure difference over the channel. Normally I would use standard methods, as frozen rotor and transient stator rotor.

In this case the blades have variable pitch. The guys at ansys gave advice to setup the model using nested rotating domains and moving meshes. In the picture I added in the first post you should be able to see the rotating domain of the turbine and the nested domains of the blades.

The simulation works well for this scenario, since I can use circular domains. Problem is that I can not make my turbine diameter larger, since the nested domains around the blades will interfere with the wall. In this case the nested domains can not be circular anymore.

I am unsure how to proceed, but a solution could be to change the geometry and remesh at each timestep. It is something I have not done before.

Any advice on how to proceed

ghorrocks · November 1, 2016, 16:49

There are tutorials on remeshing on the ANSYS customer website.

Why not just make the rotating domains a little larger than the can handle the additional motion without problems?

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October 30, 2016, 17:35		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,708 Rep Power: 143	You can edit meshes in ICEM and many other meshing software (GridGen etc). But it is usually much better to go back to the original geometry, fix the geometry and remesh. This is usually much easier than editting and existing mesh.

October 31, 2016, 03:39		#3
bolus13 Member Ruud Caljouw Join Date: Dec 2012 Posts: 45 Rep Power: 13	So, in a transient run I would change the geometry and remesh at each time step? That sounds logical to me. Do you know if this something that can be done in workbench? This is what is generally work with.

October 31, 2016, 05:18		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,708 Rep Power: 143	I may have misunderstood your question. I assumed you were talking about changing an existing mesh for a new geometry. You seem to be talking about dynamic remeshing during a run. Can you explain what you are trying to model and what the motion you expect is? Also, where does the motion come from?

November 1, 2016, 03:51		#5
bolus13 Member Ruud Caljouw Join Date: Dec 2012 Posts: 45 Rep Power: 13	I am modelling a vertical axis turbine inside a channel. The flow is driven by a pressure difference over the channel. Normally I would use standard methods, as frozen rotor and transient stator rotor. In this case the blades have variable pitch. The guys at ansys gave advice to setup the model using nested rotating domains and moving meshes. In the picture I added in the first post you should be able to see the rotating domain of the turbine and the nested domains of the blades. The simulation works well for this scenario, since I can use circular domains. Problem is that I can not make my turbine diameter larger, since the nested domains around the blades will interfere with the wall. In this case the nested domains can not be circular anymore. I am unsure how to proceed, but a solution could be to change the geometry and remesh at each timestep. It is something I have not done before. Any advice on how to proceed

November 1, 2016, 16:49		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,708 Rep Power: 143	There are tutorials on remeshing on the ANSYS customer website. Why not just make the rotating domains a little larger than the can handle the additional motion without problems?