[cfd seeker]

Originally Posted by ghorrocks

Please post an image which shows clearly which domains are rotating and which are moving mesh, and for the moving mesh domain clearly show your different boundary patches and the moving mesh boundary conditions you applied to them.

Hi,

thanks for the reply.

Image1: shows the full model

Image2: shows 5 pistons as rotating domain

Image3: shows the stationary domain comprising of inlet and outlet ports

Image4: shows the interface on the rotating domain side and defined as 'Stationary' for mesh motion

Image5: shows the interface on stationary domain side

Image6: shows the piston faces which are moving and hence defined as 'Specified Displacement' for mesh motion

Image7: shows the side walls of pistons which have been defined as 'Unspecified' for mesh motion

full_model.jpg rotating_domain.jpg stationary_domain.jpg interface_1.jpg interface_2.jpg

[cfd seeker]

Image6 and Image 7 in this post.

moving_walls.jpg

unspecified_walls.jpg

[ghorrocks]

Thanks, that explains what you are trying to do.

So is your question - why does the interface patch on the pistons deform? If so please post your CCL as well so I can check that.

[cfd seeker]

Originally Posted by ghorrocks

Thanks, that explains what you are trying to do.

So is your question - why does the interface patch on the pistons deform? If so please post your CCL as well so I can check that.

thanks for your reply. You can find the ccl of the case attached as a text document in the post.

In this case i have defined both the domains as Stationary so as to only model the movement of pistons.

[ghorrocks]

In your mesh deformation setup you have Mesh Stiffness, option increase near small volumes. Try changing this to "Value" and defining a nominal value (say, 1.0).

Also, you have double precision off. Try turning it on.

[cfd seeker]

Originally Posted by ghorrocks

In your mesh deformation setup you have Mesh Stiffness, option increase near small volumes. Try changing this to "Value" and defining a nominal value (say, 1.0).

Also, you have double precision off. Try turning it on.

Hi Glenn,

thanks for your reply. That alaso didn't help.

But in the Domain Interface when I activated the 'Nonoverlap Condition' then the mesh on the Interface is not moving. Is this mean that whole of the interface is Nonoverlaping? From the CFX modelling guide I have read that the Nonoverlap portion of interface switches to Wall.

For the refernece I am attaching the figure so that you have an idea what I am talking about.

Nonoverlap.jpg

[cfd seeker]

I think i have found the reason why the mesh on the interface is deforming. It is written in the Modelling guide that when deforming mesh is used with the Conservative Interface Flux (condition at interface), it behaves like Unspecified mesh motion and no constraint is applied on the mesh nodes.

interface.jpg

Any idea that if some trick can be applied at the interface so that the mesh should not get deformed at the interface?

[ghorrocks]

You have defined the interface side on the mesh motion domain to be stationary so it should not move. But it appears to be acting as unspecified and that is not correct. I suspect what you are seeing is a bug in CFX so it would good to report it to ANSYS support as a possible bug.

Some ideas of work arounds:
* Use specified displacement with the displacement set to zero instead of stationary.
* Cut your pistons into two domains. Have a small domain next to the interface which does not have mesh motion. This means the mesh here will be fixed. And in the other matching domain have the mesh motion to do the piston motion. You should be able to get the mesh to be contiguous across these domains so no additional interface will be necessary.

The first approach is a simple work around which might work (no guarantees). The second one will definitely work but will result in another domain.

[cfd seeker]

* Use specified displacement with the displacement set to zero instead of stationary.

I tried this but didn't work.

* Cut your pistons into two domains. Have a small domain next to the interface which does not have mesh motion. This means the mesh here will be fixed. And in the other matching domain have the mesh motion to do the piston motion. You should be able to get the mesh to be contiguous across these domains so no additional interface will be necessary.

I will try this after the weekend.

Another thing....as i mentioned in my previous posts that when i activated the Non-overlap condition and defined the mesh to be Stationary on the Non-overlap portion of Interface then the mesh on the whole of interface stops to move. So does this mean that the whole of the interface is Non-overlaping and switched to wall when Non-overlap condition is activated?

[ghorrocks]

The CCL file you attached previously did not have anything about the non-overlap option in it. If you are talking about a different model then please attach the CCL of the model you are talking about.

As I said, I suspect this is actually a bug in CFX. If you are using CFX 19.2 you should report it. If you are using an older version of CFX you should update to V19.2. If you cannot update to V19.2 then you are stuck with it because ANSYS is not going to fix a bug in an old version.

But the domain splitting idea should work fine so this is a work-around which should work regardless.