The cylindrical axis direction is along the line between two specified points P1 and P2. The radial axis is normal to the cylindrical axis and oriented toward the tail of the velocity vector. The circumferential direction is given by the cross product of these axes.
The velocity vector is specified by two angles, α and β. The first angle, α, is measured from the cylindrical axis to the projection of the velocity onto the axial-circumferential plane. The second angle, β, is measured from that projection to the velocity vector.
Last updated 5 Sep 2018