TABLE OF CONTENTS It may seem from the above discussion of the details of flow in the blade rows that any sort of design optimization based on blade section data would be spurious at best, and at worst misleading. But in fact, methods for examining the ramifications of choice of the blade Mach number, solidity, blade loading, hub-to-tip radius ratio, etc. can be very useful, provided the results are utilized as one input to the design process, along with considerations such as have been outlined above. This section outlines an approach for judging on the basis of blade section performance how the requirements for high mass flow per unit frontal area, high pressure ratio per stage, and high efficiency interact and how they may be traded against one another.
Consider the stage of figure 5.3 with inlet guide vanes. For the sake of simplicity, assume that there are no radial displacements of streamtubes and that the axial velocity is constant throughout, so that the argument is more nearly applicable to multi-stage compressors with slowly varying hub and tip radii than to a transonic stage such as that in figure 5.7. The diffusion factors for the rotor and the stator are
and
From the Euler equation,
Defining a work coefficient
| (5.32) |  |
and a dimensionless radius ? = r/ r T gives
| (5.33) |  |
where
and
If we further assume that v c ? v d = v c ? v b (that...
