[cfd seeker]

Originally Posted by Gert-Jan

As I already mentioned, you can close the gap. Then there will be a wall with zero thickness. Do not include this wall in any way in your CFD-calculation. It should be completely absent.

ok but if I don't include the connecting wall then the mesh of suction and pressure sides will be totally disconnected from eachother and the interface side of stationary parts will be discontinous from eachother. Can CFX handle this?

Also as per my understanding the interface should be exactly same on both the sides?

Needles to say, that if the goal of your CFD-study is to the determine the flow through the gap, then you should not apply this simplification. But that depends on the question that you are trying to answer using CFD.........

the pump has already been designed and working. Purpose is to get the simulation model of pump so that the effect of variation of different parameters on pressure delivered by the pump can be studied e.g increasing no. of pistons.

[Gert-Jan]

Originally Posted by cfd seeker

ok but if I don't include the connecting wall then the mesh of suction and pressure sides will be totally disconnected from eachother and the interface side of stationary parts will be discontinous from eachother. Can CFX handle this?

Yes. No problem

Originally Posted by cfd seeker

Also as per my understanding the interface should be exactly same on both the sides?

No, not necessary. Certainly, if you have a coarse mesh on either side, it will affect your solution. Therefore, you could perform some tests to check their influence.

[cfd seeker]

thanks for your help. I will try this and will share the results.

One more thing. If i include the connecting wall between suction and pressure ports and just consider it as a part of interface on both sides of interface, will it gonna work?

[cfd seeker]

Originally Posted by Gert-Jan

Yes. No problem



No, not necessary. Certainly, if you have a coarse mesh on either side, it will affect your solution. Therefore, you could perform some tests to check their influence.

For the interface model which model i can use? When I am using the transient-rotor stator I am getting the following error as seen in the figure attached with the post.

interface.jpg

Any idea?

[Gert-Jan]

Turn on the expert parameter?

[cfd seeker]

Even with frozen Rotor it's not working because I think the pistons are not getting the right motion.

For the mesh motion i have defined 5 local coordinate systems at the interface surface of each piston as seen in the figure1. I set to rotate the local coordinate frame at the same rotational speed so that I can easily define the displacement of each piston in each local coordinate system (e.g. for local coordinate system of piston1 as seen in figure 2) . But when i define the rotational speed of local coordinate system then i can't access this coordinate system under the boundary condition panel as seen in figure 3. In such a case how i can refer the local coordinate system for definition of Mesh displacement?

interface1.jpg interface2.jpg interface3.jpg

[cfd seeker]

Just a simple question. When I load the mesh in CFX then CFX automatically places Global coordinate system centre at the centre of body as shown by the red dot in the attached figure. centre.jpg

I am asking this because I don't know the location of Global coordinate system and I am just specifying 'Global Y' as rotation axis.

[Gert-Jan]

I know it is possible with immersed solids. I can share an example which is different but contains the similar settings.
I don't know with moving mesh. Maybe there is a limitation on moving mesh in combination with a rotating domain. I doubt it, but if you want to be sure I would ask the Support for an example.

[Gert-Jan]

Originally Posted by cfd seeker

Just a simple question. When I load the mesh in CFX then CFX automatically places Global coordinate system centre at the centre of body as shown by the red dot in the attached figure.

I am asking this because I don't know the location of Global coordinate system and I am just specifying 'Global Y' as rotation axis.

I don't understand this. If I am correct, CFX creates the Global Axis on the origin (0,0,0). As a check, you can always create a monitoring point with certain coordinates to find where you are in the geometry.

[ghorrocks]

I have use moving mesh and TRS to model rotary sliding valves many times and it works fine for me. But I do not use moving mesh and rotating frames of reference on the same domain. I have a domain either moving mesh or rotating frame of reference, but not both.

[cfd seeker]

Originally Posted by Gert-Jan

I know it is possible with immersed solids. I can share an example which is different but contains the similar settings.
I don't know with moving mesh. Maybe there is a limitation on moving mesh in combination with a rotating domain. I doubt it, but if you want to be sure I would ask the Support for an example.

Yes please share the example.

[cfd seeker]

Originally Posted by Gert-Jan

I don't understand this. If I am correct, CFX creates the Global Axis on the origin (0,0,0). As a check, you can always create a monitoring point with certain coordinates to find where you are in the geometry.

If the geomtery is not centered around Global axis (0,0,0) then is there a way to move the mesh to centre in CFX or i have to go back and reorient it in meshing module?

The second option is to define the rotation axis using Two Points Option i.e. Rotation axis from and Rotation axis to...but i am not sure what is meant by this? Do you have any idea or example?

[cfd seeker]

Originally Posted by ghorrocks

I have use moving mesh and TRS to model rotary sliding valves many times and it works fine for me. But I do not use moving mesh and rotating frames of reference on the same domain. I have a domain either moving mesh or rotating frame of reference, but not both.

I am not sure if I place a local coordinate system on a rotating face then the local coordinate system will rotate with it not?

If domain is rotating and i also specify a rotation for local coordinate system then this coordinate system is no more available under the boundary conditions tab as shown in the picture in the above posts. I asked the support guy but he was not sure about it and he said that he will tell me later.

[Gert-Jan]

Originally Posted by cfd seeker

If the geomtery is not centered around Global axis (0,0,0) then is there a way to move the mesh to centre in CFX or i have to go back and reorient it in meshing module?

Certainly you can move the mesh in Pre. Go to the mesh i nhe top of your tree and use your RMB for option to translate, scale, rotate or mirror it.

Originally Posted by cfd seeker

The second option is to define the rotation axis using Two Points Option i.e. Rotation axis from and Rotation axis to...but i am not sure what is meant by this? Do you have any idea or example?

Just define two points, e.g. [0,0,0] and [0,1,0] to rotate around the line through those points (the y-axis in this example). But you can use any number. CFX is flexible.......

There is also an option to create a coordinate frame based on the normal of a surface. Convenient if you don't know its, center.
Remember you can find coordinates using the creation of monitor points.

[Gert-Jan]

Originally Posted by cfd seeker

I am not sure if I place a local coordinate system on a rotating face then the local coordinate system will rotate with it not?

That is why I advised to create a very simple geometry and calculate the movements of all objects without calculating the flow. To first find out how everything behaves and moves like you want. Start simple..........

[Gert-Jan]

Originally Posted by cfd seeker

Yes please share the example.

I had this example in mind, showing the use of multiple coordinate systems in 1 simulation. It shows the movement of rotating immersed solids in a rotating domain. There is no flow. I hope it helps.

[Gert-Jan]

Can't upload it somehow. You can download it here: https://we.tl/t-jk5dTykpvB

[cfd seeker]

Hi,

thanks a lot for your reply. I will look at your example.

I am facing another problem. The pistons are getting the right movement but the interface side which is on the rotating domain side, is also moving. Although i have defined the 'Mesh Motion' to 'Stationary' on this side of interface but still the mesh is moving. This can be identified by the figures attached with the post.

mesh_movement.jpg

mesh_movement1.jpg

The reason which came to my mind is that it is not a wall but a fluid interface, so the mesh nodes on interface are also moving but not exactly as the pistons. Any idea how i can keep the mesh on this interface as stationary?

[Gert-Jan]

I don't have a lot experience with deforming mesh.

[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.