Handbook of Turbomachinery Second Edition Revised - Ventech!

velocity-compounded arrangement in 1896). The fundamental difference
between velocity-compounded stages and DeLaval stages can be seen in Fig.
11. The exit flow from the first rotor, still possessing considerable kinetic
energy, is turned by a set of stator vanes, although no expansion is intended
across these vanes. The flow then impinges on the second rotor, where
additional work is extracted. Although additional rotor rows are certainly
possible (and may be desirable under some circumstances), two velocitycompounded
rows have proven sufficient in production units with which
this author is familiar. If we refer to Fig. 9, we can see that at velocity ratios
less than approximately 0.25, multiple-row velocity-compounded turbines
can offer performance that is superior to that of a single rotor turbine. It
should also be noticed that the peak efficiencies offered decrease as the
number of rows increases due to higher frictional losses being absorbed by
the increasing turbine wetted area. When designing a multiple-row velocitycompounded
turbine, an issue of the work split between the rotor rows must
be addressed by the designer. The exact work split will depend somewhat on
the loading conditions for a particular design. However, it should be
Figure 11 Arrangement of various turbine rotor/stator blade configurations: (a)
single-rotor impulse stage, and (b) two-row velocity-compounded stage.
Copyright © 2003 Marcel Dekker, Inc.