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National Advisory Committee for Aeronautics, Research Memorandum - Investigation of the I-40 Jet Propulsion Engine in the Cleveland Altitude Wind Tunnel - II - Analysis of Compressor Performance Characteristics

Performance characteristics of the centrifugal compressor of
the I-40 Jet-propulsion engine were determined with the engine
installed in an airplane fuselage in the Cleveland altitude wind
tunnel. A standard 1-40 turboJet engine was used in the investi-
gation, which was conducted over a range of simulated altitudes
from 10,000 to 40,000 feet and ram pressure ratios from 0.98 to
1.76. During the investigation the compressor Mach number varied
from 0.72 to 1.46. Performance characteristics are presented as
functions of corrected air flow and compressor Mach number.

From results obtained over a wide range of altitudes, it was
determined that the compressor performance is primarily dependent
on the compressor-inlet Mach number. Variations of Reynolds number
of the air at the compressor inlet had little effect on compressor
performance. at low compressor Inch nmhers, increased ram pressure
ratios so shifted the compressor operating line that lower compres-
sor pressure ratio, édfipfea‘sof efficiency, and compressor pressure
coefficient was obtained at a given corrected air flow. At high
compressor Mach numbers, the effect of ram pressure ratio was
negligible. fine maximum compressor efficiency obtained was 72 per-
cent at static conditions. At 'a. corrected engine speed of 11,500 rpm,
the compressor efficiency was 69 percent, the corrected compressor
air flow was 77 pounds per second, the compressor pressure ratio
was 3.95, and the cdmpre'ssor pressure coefficient was 0.65. Special
attempts to produce compressor surge were unsuccessful.

An investigation of the I-éO Jet-propulsion engine installa-
tion in an airplane fuselage has been conducted in the Cleveland
altitude wind tunnel. Over-all engine characteristics of the
installation are presented in reference 1.

One of the objectives of the investigation was to investigate
the compressor characteristics and determine how effectively the
compressor operated in this engine. The over-all efficiency of a
turbojet engine is directly dependent on the separate efficiencies
of its component parts. In order to obtain the maximum possible
efficiency from the engine, the compressor must therefore be oper-
ated as near peak efficiency as possible. An analysis of the per-
formance characteristics of the 1-40 compressor is presented. The
compressor characteristics are presented as functions of corrected
air flow and compressor Mach number.