Page 218 - Fluid Mechanics and Thermodynamics of Turbomachinery

CHAPTER 7

Centrifugal Pumps, Fans and

Compressors

And to thy speed add wings. (MILTON, Paradise Lost.)

Introduction
This chapter is concerned with the elementary flow analysis and preliminary
design of radial-flow work-absorbing turbomachines comprising pumps, fans and
compressors. The major part of the discussion is centred around the compressor
since the basic action of all these machines is, in most respects, the same.
Turbomachines employing centrifugal effects for increasing fluid pressure have
been in use for more than a century. The earliest machines using this principle
were, undoubtedly, hydraulic pumps followed later by ventilating fans and blowers.
Cheshire (1945) recorded that a centrifugal compressor was incorporated in the build
of the whittle turbojet engine.

For the record, the first successful test flight of an aircraft powered by a
turbojet engine was on August 27, 1939 at Marienebe Airfield, Waruemunde,
Germany (Gas Turbine News (1989). The engine, designed by Hans von Ohain,
incorporated an axial flow compressor. The Whittle turbojet engine, with the
centrifugal compressor, was first flown on May 15, 1941 at Cranwell, England
(see Hawthorne 1978).

Development of the centrifugal compressor continued into the mid-1950s but, long
before this, it had become abundantly clear (Campbell and Talbert 1945, Moult and
Pearson 1951 that for the increasingly larger engines required for aircraft propulsion
the axial flow compressor was preferred. Not only was the frontal area (and drag)
smaller with engines using axial compressors but also the efficiency for the same
duty was better by as much as 3 or 4%. However, at very low air mass flow rates
the efficiency of axial compressors drops sharply, blading is small and difficult to
make accurately and the advantage lies with the centrifugal compressor.
In the mid-1960s the need for advanced military helicopters powered by small gas
turbine engines provided the necessary impetus for further rapid development of the
centrifugal compressor. The technological advances made in this sphere provided
a spur to designers in a much wider field of existing centrifugal compressor appli-
cations, e.g. in small gas turbines for road vehicles and commercial helicopters as
well as for diesel engine turbochargers, chemical plant processes, factory workshop
air supplies and large-scale air-conditioning plant, etc.
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