Handbook of Turbomachinery Second Edition Revised - Ventech!

compressors as long as the desired pressure rise was low enough to be
conveniently measured in inches of water. Compressor efficiency deteriorated
when greater pressure increases were sought, falling below the order of
0.7 when pressure ratios of about 2, or higher, were needed.
During the mid-1930s the interest in compact, lightweight compressors
for supercharging the reciprocating engines of military aircraft spurred
research and development efforts having the goal of realizing efficiencies of
0.8 or higher when the developed pressure ratio was at least 3. By this time,
other research had augmented the understanding of fluid mechanics and
aerodynamics to the point where the important interactions between blades
and fluid could be identified and the chief causes of losses in efficiency
understood.
Of particular value was the concept of boundary layers, which
contained most of the fluid affected by friction and which partially blocked
the area provided for the flow. It had also been discovered that boundary
layers, when once formed, often moved in different directions than that of
the adjacent main stream.
Systematic work could then be planned to attack the problems. A
summary of this effort on axial-flow compressors, up to about 1955, is
presented in Reference [1]. A subsequent review is provided by Lakshminarayana
[2]. Research has continued, and compressors developing pressure
ratios of the order of 20 with adiabatic efficiencies 0.80 or more are feasible.
Pertinent references to similar research on centrifugal compressors and to
the more recent work on all compressors are noted as the need arises.
The design of compressors usually requires a number of steps. After
studying the various requirements for an intended compressor, a designer
selects for the design point the values for the total pressure and temperature
of the inlet gas flow, the rate of mass flow, the pressure ratio, and the target
efficiency. The designer also selects tentative values for both the outer and
inner diameters of the annulus for the first row of blades. A rotating speed
for the rotor is also assumed. These choices are usually made at the
condition where either the highest efficiency or the greatest pressure ratio is
demanded. In addition, the designer decides how to compromise the often
conflicting requirements of low operating costs, low manufacturing costs,
small size, light weight, and high reliability.
A designer then chooses the mean gas velocity, or Mach number, at
the compressor inlet, and also decides what changes in velocity components
each of the blade rows should produce. These estimates are made at a
number of radii in the inlet annulus of the flow passage.
The designer can then estimate the radial movement of the streamlines
as the flow passes through the first set of blades. Changes in the pressure and
temperature produced by the row can now be calculated. This is done at
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