Handbook of Turbomachinery Second Edition Revised - Ventech!

The next generation of machinery entered design at about the same
time as the Redstone engine was beginning flight operations. The U.S. Air
Force called for the design of an intermediate-range ballistic missile (IRBM)
to be stationed in England. The missile carried the name Thor and was
designed for a range of 1,500 miles. The engine required for the Thor
represented a large jump in capability from the Redstone engine. Thrust of
the engine was to double, as was the chamber pressure, reaching just under
600 psi. Liquid oxygen was retained as the oxidizer, with kerosene being
substituted for ethyl alcohol as the fuel for higher performance. Fuel and
oxidizer flow rates required increased to 200 lb/sec and 450 lb/sec,
respectively. The corresponding pump head rises were 1,650 ft and
2,340 ft. Simple calculations will show that the required turbine power for
this application was in excess of four times that of its Redstone predecessor.
This large increase in required performance resulted in a number of
significant evolutionary changes.
First, the large turbine power requirement rendered the previous
hydrogen peroxide monopropellant drive system less practical. In order to
more compactly package both the turbine and its drive system, a small
combustor was incorporated to produce the turbine drive gas. Called
(predictably) a gas generator, this small chamber burned the engine’s main
propellants to produce hot, fuel-rich gas at a temperature of approximately
1,200 8F. The output of the gas generator was, of course, ducted directly to
the turbine inlet where the gas was expanded through a two-stage impulse
turbine. To produce the required power (approximately 3,100 hp), the
turbine’s two stages expanded 15 lb/sec of drive gas through a pressure ratio
of 17.6. Upon exit from the turbine, the gases were exhausted to the
atmosphere.
Another fundamental change also concerned turbine packaging. In
order to produce the required shaft power with reasonable efficiency, a
much higher turbine blade speed was required. To accomplish this along
with reducing the turbine weight and volume, turbine rotational speed was
increased by a factor of in excess of 7, to 30,500 revolutions per minute.
Together with a decrease in turbine pitchline diameter from 20 in. to 9 in., a
blade speed increase from 400 to 1,200 ft/sec was obtained.
The centrifugal pumps for the Thor engine also underwent noticeable
improvements. Since the fuel and oxidizer were of comparable density, the
required head rises from both pumps were also similar. This enabled both
pumps to again be placed back to back on a common driveshaft, which
required both pumps to run at the same angular velocity. To generate the
increased head required over that of the Redstone engine, the diameter of
both pump impellers was increased, and their operating speed was increased
to 6,300 rpm. The increased performance demand resulted in a great
Copyright © 2003 Marcel Dekker, Inc.