Hi to everyone,
Very silly question here. But i have not found a proper answer yet. Given the velocity profile in the coordinate direction (U_X, U_Z) over a plane XZ plane, with Y normal, (i.e in my case a slice of an annular duct) i have to compute the radial and tangential velocity. Is so right the following procedure?

Compute the angle alfa with the phyton calculator as suggested here [quote=“Kyoshimi, post:2, topic:12796, username:KenichiroYoshimi”]
arctan2(points[:,2], points[:,0])
[/quote]. In my case i put [:,2] since the coordinate is along the Z direction; 
Estimate the following scalars simply using the calculator
U_rad=U_X*cos(a)+U_Z*sin(a);
andU_tan=U_Z*cos(alfa)U_X*sin(alfa);
. Where U_X and U_Z are scalars too.
Have i to add something else (e.g the coordinate results as option)? Or must i consider the vectorial product (e,g including IHat and kHat)?
I know it’s a trivial question but i want to be sure of this.