[MazenDraw]

I am running a dynamic mesh case (AMI), where the moving zone rotates around the z-axis. A usual rotor-stator case. When I'm using the fieldaverage utility however I am not sure what the results are representing in the rotating zone.

• Does the tool use the absolute velocity or the relative velocity in the rotating zone?
• Is the averaging performed on moving mesh cells ID's or static points in the domain?

Attached you find two images. One for the simultaneous velocity and the other for the mean velocity. The image with the mean velocity shows the rotating zone with low velocity values in the rotating zone.


Thanks for your help!

[MazenDraw]

After some more investigation, I realized that this is the absolute velocity. The thing is that the rotating zone is rotating around z-axis. The averaging performed in the tool is applied to the absolute velocity x, y and z components. Therefore, as the rotating zone rotates with time, x- and y-velocity components cancel each other. The only thing that stays after averaging is the z-component, hence the previous attached plot.


For now, I chose to calculate the magnitude of the absolute velocity vector and cumulatively average it with time. I have done this manually on points of interest.

[louisgag]

Hi, thanks for sharing your findings.
I would add that, when the mesh rotates, the mean is taken per cell/face.
These cells/faces rotate and thus sample different geometric points in your domain at each timestep.

You end up having, in your rotating zones, a mean which is only valid as seen as "moving with the cell"...
So if you had a rotating cylinder mesh with nothing inside of it with a constant velocity flow streaming through it, your mean would still end up looking incoherent.

[SSSERB13]

Hi MazenDraw,
I am dealing with this situation now and I am questioning if my results are right or not. When using the velocity magnitude to see the results we can see a big velocity gradient outside the moving region, however, the case is running well. How I can evaluate these two fields or stationary and rotating frame in OF?

Please find attached the image that illustrates the velocity magnitude results.