SRF (Single Rotating Frame)
 

Dear friends,

Is it possible (in CFX) to simulate a rotating domain without any stationary region?
In other words, can I simulate a rotating domain by using SRF without any stationary domain or boundaries?


Best Regards
Sasan Ghomi

Yes. For example, you can setup a simple cilindrical volume and let it rotate around its central axis. It can contain parts that rotate with the cilindrical volume.

On top of of that, you can set the outer wall to be counter rotating. In such a case it is standing still, effectively. Then you have a stationary object in your rotating domain. So, without having a stationary domain, you can have a stationary object. But you don't need that, if I read it correctly.

Thank you.

What do you mean by this?
Is there any need for stationary boundaries?

Strictly there is no need. But then you only get a solid body rotation. You don't need CFD for that.

So what do you want to simulate?

Thank you.
Regarding my simulation,
I am simulating the fluid flow inside a pipe which is rotating around an axis.
Can I define the whole domain as a rotating domain? In doing so, there would not be any need for frozen rotor interfaces.
So, I suppose that such simulation is called Single Rotating Frame (SRF).

Best Regards

Yes, this model is possible. Yes, you define the whole fluid region as a rotating domain. Which axis is the pipe rotating about?

Does it make any difference? The pipe is rotating around an axis parallel to it own axis.
Please let me know if there is any difference!!

In this case you have to be careful to define inlet and outlet boundary conditions to account for the frame change. But it should work fine as long as that is sorted.

It is said that SRF can only simulate steady problem, so I am not sure if it is suitable fot your problem.

That is not true. It is possible to run a transient case with single rotating of reference. I did it yesterday,.......

Out of curiosity, I wonder if it is possible to break it down to a stationary case? If the rotation rate is very high, maybe gravitational effects can be neglected even if the axis does not coincide with the height-axis. Then the rotation can be accounted for by a constant "radial" force which should be easy to implement with another coordinate system coinciding with the rotation axis. This would allow for easier definition of other BCs. Maybe I miss something though.

CFX or Fluent?
 

Actually, I am running the case. I used SRF and got a steady result. Then, when I change the simulation type to transient. the scaled residual line seemed unchanged. However, when I changed the 'cell zone condition' to 'Mesh Motion', the line seemed more normal(lines ups and downs). So I thought SRF may be not suitable for unsteady simulation.:o
My software is FLUENT and case is rotating channel. For SRF, 'cell zone condition' is 'Frame Motion'.

It makes sense in theory. However, When I calculated a rotating channel using SRF(got a steady result). When I change the simulation type to transient. The scaled residual line seemed unchanged(abnormal). However, when I changed the 'cell zone condition' to 'Mesh Motion', the line seemed more normal(lines ups and downs).