Handbook of Turbomachinery Second Edition Revised - Ventech!

Figure 15k H–Q characteristics for several typical pumps.
could fall along the curve labeled ‘‘shallow depth of stall’’ in Fig. 15(k). The
principle here is simply that the more diffuser rows continue to operate, the
shallower is the depth of stall. On the other hand, if a diffuser in one of the
‘‘early’’ stages of the pump stalls, the velocity diagrams in all subsequent
stages are likely to be upset, resulting in a near total collapse of their
developed head. The further toward the pump inlet the stall propagates, the
steeper is the depth of stall.
The propensity of multistage axial-flow pumps to perform in the
manner described above has discouraged their application in modern liquid
rocket engine systems. It should also be noted that attempts at ‘‘aggressive’’
packaging for weight savings (i.e., fewer pump stages, more highly loaded
stages, etc.) will only aggravate this tendency. It is a fact that axial-flow
pumps designed with an effort toward weight conservation have been unable
to support significant thrust-level changes of the engine systems and, in one
instance, have been unable to support the engine system starting transient.
In this last case, elaborate prestart procedures and special control system
considerations were necessary to ensure satisfactory engine starts.
Inducers
The continued tendency to optimize launch vehicle design for minimum
inert structural weight is well known. Since the propellant tanks of a large
liquid propellant launch vehicle are typically the largest pieces of vehicle
Copyright © 2003 Marcel Dekker, Inc.