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National Advisory Committee for Aeronautics, Report - Extension of Useful Operating Range of Axial Flow Compressors by Use of Adjustable Stator Blades

A theory has been developed for resetting the blade angles of
an arialjlow compressor in order to imp-race the performance
at speeds and flows other than the design and thus extend the
useful operating range of the compressor. The theory is
readily applicable to the resetting of both rotor and stator blades
or to the resetting of only the stator blades and is based on
adjustment of the blade angles to obtain lift coejicients at which
the blades will operate ejiciently.

Calculations were made for resetting the stator blades of the
NACA eight-stage aerialg‘low compressor for 7’5 percent of
design speed and a series of load coejicients ranging from 0.28
to 0.70 with rotor blades left at the design setting. The NAC’A
compressor was investigated with three dijerent blade settings:
(I) the design blade setting, (2) the stator blades reset for 7'5
percent of design speed and a load coejicient of 048, and (3)
the stator blades reset for 75 percent of design speed and a
load coejicient of 0.65. blast of the tests were conducted at
an inlet-air pressure of 10.16 inches of mercury absolute and
an inlet-air temperature of 0° F and extend over a range of
compressor hfach numbers from 0.2 to 0.8 for the three blade
settings. In order to investigate the eject of inlet-air condi-
tions at low speeds, tests at a compressor .Mach number of 0.2
were repeated for the first blade resetting with standard sea-
lerel inlet-air conditions.

The experimental results show that a substantial increase in
the useful operating range of axialg‘low compressors can be
obtained by adjustment of only the stator-blade angles. 00n-
siderable improvement in ejiciency at compressor hdach num-
bers appreciably below the design value was obtained for both
stator-blade resettings. A difference of .90 to 30 percent in the
pealc-ejlciency flows for the two stator-blade resettings also was
obtained, which at high compressor speeds was about seven
times the maximum flow range for a particular blade setting.