velocity angle not calculated correct
 

I have a case in which I am looking at areal-weighted average axial and tangential velocities and at areal-weighted average velocity angle. I am collecting my values in the surface integral box.

But when I calculate the velocity angle myself, I get nowhere near the same value. Fluent reports an angle between 20 and 175 deg and I calculate angles between 0.2 and 8 deg. I use the formula angle=atan(tangential/axial), and the tangential and axial velocities is the ones reported by fluent.

Does anyone know if this may be due to that Fluent maybe is calculating the angle at all the individual nodes and then integrates and if large deviations between nodes may differ from the average net result given by fluent?

It seems to me that if I take the net value given by fluent, I should be able to calculate the same angle as fluent reports as the net value.

I do not understand this.

Cheers