[Kendas]

I define a local coordinate system and don't know how to calculate the velocity components of the defined local coordinate system.

[ghorrocks]

What do you want to do with the velocities in your coord system? For most things on CFD-Post the coord system does not matter as the velocity vector looks the same regardless of the coord system. So for most visualisations of velocities inside CFD-Post the coord system does not matter.

If you are exporting it then there is an option to define what coord system to use.

[Kendas]

As shown in the attached image, there are three outlet, and I want to obtain the velocity components in the circumferential, radial, and axial directions for each outlet.

[ghorrocks]

Do you want a single representative velocity vector at each outlet? ..... if so, then get the velocity components in the absolute frame from the average velocity over the patch, then do your own transform into your coord system

Or do you want the whole velocity distribution over the outlet patches? .... if so, it depends on what you want to do with it.

[Kendas]

Yes, I want a single representative velocity vector at each outlet.
However, I am not sure how to transform the results into my coord system, even though I have been reading the manual.

[ghorrocks]

You do not do it in CFX or CFD-Post. This is just a few equations and you do it yourself.

This page has an excellent description of coordinate transforms: https://stackoverflow.com/questions/...tem-to-another

[Kendas]

Thank you. I'll try it myself.