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National Advisory Committee for Aeronautics, Technical Notes - Theoretical Performance of an Axial Flow Compressor in a Gas Turbine Engine Operating with Inlet Water Injection

The theoretical performance with inlet water injection of an axial—
flow compressor operating as a component of a gas—turbine engine is
evaluated for normal compressor pressure ratios of 4, 8, and 16. Cone
tinuous saturation throughout the compression process is assumed. The
assumptions of choked turbine nozzles and a compression efficiency at
any point in the compressor dependent on the evaporative cooling prior
to that point are used to determine the changes in mass flow, compressor
pressure ratio, compressor work, and over—all compressor efficiency.

The analysis indicates that the compressor work per pound of turbine
gas flow is lower with inlet water injection than without even for
conditions where large decreases in compressor efficiency occur; con-
sequently, engine output per pound of turbine gas flow is greater with
injection than without.

Numerous investigations of the augmented performance of turbojet
engines with liquid injected into the engine inlet have been made
(references 1 and 2, for example). These investigations have generally
been based on the assumption of equal turbine—work outputs during
normal and augmented operation, and of a constant compressor slip
factor with or without augmentation. These assumptions are more
applicable to the centrifugal-compressor turbojet engine than to one
having an axial—flow compressor and have afforded a satisfactory
correlation between theoretical and experimental thrust augmentation
values for a centrifugal-type engine.

In order to provide a better insight into the performance of an
axial-flow compressor with inlet liquid injection, a method was developed
at the NACA Lewis laboratory for predicting the compressor performance
under these conditions. The details of the method and the calculated
performance of axial-flow compressors with water injection are presented
herein.

The method evaluates the compressor performance when saturation is
maintained during the compression process. variations in compressor
mass flow with liquid injection and in compressor efficiency with
evaporative cooling are included in the analysis.