Dear all,

I'm Mattia and I'm a PhD student at the Delft University of Technology (The Netherlands).

At the moment, I am analysing a radial compressor by means of CFD: I am using GAMBIT 2.3.16 for mesh generation and FLUENT 6.3.26 for simulations.

At first, I am using a single rotating frame, which means that everything is rotating (both inlet and outlet basically, because that compressor does not have any diffuser).

Now, my big concern/doubt is the axis of rotation. In the manual is it said that "For 3D problems - and this is my case -, the axis of rotation is the vector from the Rotation-Axis Origin in the direction of the vector given by your Rotation-Axis Direction inputs". Thus, if I select, for the rotation axis direction x=1 y=0 z=0, it means that the direction of rotation is around x-axis.

Well, if the x-axis is going into the screen (in order to talk easily), this means that the rotation should be clockwise, isn't it?

Anyway, how can I be 100% about the direction of rotation in those terms?

I hope I could express my idea.

Thank you. Kind regards, Mattia.

Yes, you expressed your thoughts and ideas very clearly. You can check your solution by plotting relative and absolute velocity vectors. The relative vector plot is ratating with the control volume... the absolute vectors should illustrate the rotation of your control volume, with teh relative vectors superimposed. The difference in magnitudes should be the (omega)*(radius) magnitude.

Thank you.

But what do you exactly mean with ABSOLUTE VELOCITY VECTORS?

I cannot find that quantity in the VECTORS panel.

Regards, Mattia.

From the main window --> Display Vectors --> Vectors of: (2 choices available... a) "velocity" = absolute velocity, or b) "relative velocity" = velocity relative to the control volume specification) Hope this helps...

Yes, it does.

Btw, only then I realized that "velocity magnitude" is the absolute one, because the "relative velocity" is explicitly expressed.

thank you.