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2.2 Linear Cascades
This choice was very often made in the past. It has the disadvantage that application
of the goniometric tangent function is difficult. Due to the general use of electronic
calculation devices, the first convention (axial convention) is preferred at present,
with angles varying from − 90° to + 90°. This convention has already been applied 
systematically in Chap. 1. For the entire book, we exclusively reason on left turning machines. Both left and right turning machines actually occur in practice (some
illustrations concern right turning machines). More generally, we take a coordinate
frame with first axis in the meridional direction (this is the tangent to the intersection of the average circumferential streamsurface with a meridional plane), positive
into the through-flow sense; second axis in the circumferential direction, positive
in the running sense; third axis perpendicular to the average streamsurface, positive
in the outward sense.
Fig. 2.12 Force exerted onto a cascade blade (rotor pump)