Section 2.1.1 - Centrifugal Pump Theory - Axial-Flow Pumps

Axial-Flow Pumps   The preceding development, though general, is applicable mainly to
centrifugal and mixed-flow pumps. In that procedure, the impellers have appreciable solidity,
and original blade shapes are constructed from the viewpoint of one- or two-dimensional
channel flow. The collectors are often volutes or non-axial-flow vane systems. Performance
is not known a priori and so must be estimated, as outlined further on. On the other hand,
the extensive two-dimensional, experimental, axial-flow cascade data amassed by NACA
researchers²³ and others enables the designer to adopt existing airfoil blade shapes and so
predict the performance with greater confidence. The procedure for utilizing these shapes
and the corresponding experimental results has long been the basis for designing axial-flow
compressors for gas-turbine engines and is clearly described by Hill and Peterson³⁵.
This approach is widely used, especially for high-specific-speed, low-solidity axial-flow
propeller pumps—in designing both rotating and stationary blade rows. Insights for propeller
pump design and performance characteristics can be found in Stepanoff.⁵

An exception to this axial-flow pump design approach is the case of inducers. Although
they are axial-flow pumps, they have high solidity and are usually designed as channel-
flow machines. The design philosophy outlined in the preceding paragraphs is applicable,
except that the blades usually approximate constant- or variable-pitch helices. Performance
prediction is generally accomplished via one-dimensional calculations and the correlations
described in the following paragraphs and, increasingly, via CFD analysis.