naca-rm-e9l01
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National Advisory Committee for Aeronautics, Research Memorandum - Temperature and Pressure Distribution in Dual Parallel Jets Impinging on the Ground from a Turbojet Engine
An investigation was conducted to determine the temperature
and pressure distributions in the Jets issuing from two parallel
nozzles of a turboJet engine located close together and impinging
on the ground at an angle of 20°. The investigation was limited
to the following conditions:- convergent nozzles; nozzle diameter,
13 inches; nozzle spacing, 1.42 nozzle diameters; Jet total temper-
ature, 15500 to 17500 R; and nozzle-pressure ratio, 1.44 to 1.52.
Temperature and pressure profiles obtained indicated a pro-
nounced mutual interference between the Jets beyond 1 diameter
downstream.of the nozzle exists. The Jet boundary was found to
be farther above the ground between the two-Jets than it was
directly behind either of them. In the portions of the Jets
unaffected by the interference, expansion of the gases was
mostly horizontal; very little vertical rise was observed.
The need for greater power in high-speed Jet aircraft has
led to consideration of designs incorporating two Jet engines
installed side by side in the fuselage with the exit nozzles
located considerably forward of the tail surfaces. The tail sur-
faces can be so placed as to be well above the wakes of the Jets
during flight. The take—off angle is such, however, that air-
planes with short landing gears may operate with the Jets imping-
ing upon the runway. During such operation, the Jets may be
deflected into the tail-surface region and cause excessive
heating and failure. The possibility of using afterburning as
a means of thrust augmentation during take-off makes this problem
even more serious, as the temperature of the exhaust gases would
be much higher.
A full-scale engine investigation to determine the tempera—
ture and pressure distributions in the wake of two adjacent
parallel Jets impinging on the ground at an angle of 20° simu-
lating a nose-high take-off condition was conducted at the NACA
Lewis laboratory. The measurements are presented in nondimenp
sional terms to make them applicable to other Jet diameters and
gas temperatures.
The engine used for this investigation has a dual-entry
centrifugal compressor, 14 combustion chambers, and a single-
stage turbine. The sea-level static thrust rating is about
4000 pounds.
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