Page 255 - Fluid Mechanics and Thermodynamics of Turbomachinery

CHAPTER 8

Radial Flow Gas Turbines

I like work; it fascinates me, I can sit and look at it for hours. (JEROME
K. JEROME, Three Men in a Boat.)

Introduction
The radial flow turbine has had a long history of development being first conceived
for the purpose of producing hydraulic power over 170 years ago. A French engineer,
Fourneyron, developed the first commercially successful hydraulic turbine (c. 1830)
and this was of the radial-outflow type. A radial-inflow type of hydraulic turbine
was built by Francis and Boyden in the U.S.A. (c. 1847) which gave excellent
results and was highly regarded. This type of machine is now known as the Francis
turbine, a simplified arrangement of it being shown in Figure 1.1. It will be observed
that the flow path followed is from the radial direction to what is substantially an
axial direction. A flow path in the reverse direction (radial-outflow), for a single
stage turbine anyway, creates several problems one of which (discussed later) is
low specific work. However, as pointed out by Shepherd (1956) radial-outflow
steam turbines comprising many stages have received considerable acceptance in
Europe. Figure 8.1 from Kearton (1951), shows diagrammatically the Ljungstr¨om
steam turbine which, because of the tremendous increase in specific volume of
steam, makes the radial-outflow flow path virtually imperative. A unique feature of
the Ljungstro¨ om turbine is that it does not have any stationary blade rows. The two
rows of blades comprising each of the stages rotate in opposite directions so that
they can both be regarded as rotors.
The inward-flow radial (IFR) turbine covers tremendous ranges of power, rates of
mass flow and rotational speeds, from very large Francis turbines used in hydroelec-
tric power generation and developing hundreds of megawatts down to tiny closed
cycle gas turbines for space power generation of a few kilowatts.
The IFR turbine has been, and continues to be, used extensively for powering
automotive turbocharges, aircraft auxiliary power units, expansion units in gas lique-
faction and other cryogenic systems and as a component of the small (10 kW) gas
turbines used for space power generation (Anon. 1971). It has been considered
for primary power use in automobiles and in helicopters. According to Huntsman
(1992), studies at Rolls-Royce have shown that a cooled, high efficiency IFR turbine
could offer significant improvement in performance as the gas generator turbine of a
high technology turboshaft engine. What is needed to enable this type of application
are some small improvements in current technology levels! However, designers of
this new required generation of IFR turbines face considerable problems, particularly
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