Experimental investigation of effect of cooling air on turbine performance of two turbojet engines modified for air-cooling Page: 3 of 36

                                
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NACA RM E55J19

an increase in blade profile losses due to heat removal by the coolant;
the experimental tests of reference 7 were obtained with no temperature
difference between the main gas stream and the coolant.
The present investigation was undertaken at the NACA Lewis lab-
oratory in order to explore the effect of radial discharge of cooling
air from the blade tips on turbine performance at current operating
temperatures. A centrifugal-compressor engine and an axial-flow-
compressor engine were modified for air-cooling and operated at sea-
level static conditions to provide a comparison of uncooled- and cooled-      D
turbine efficiency over a range of turbine operating conditions. The
centrifugal-compressor engine was operated over a range of equivalent
turbine speeds from 93 to 102 percent of design (both cooled and un-
cooled) and coolant- to gas-flow ratios from 0 to 0.08. The axial-flow-
compressor engine was investigated over a range of equivalent turbine
speeds from 70 to 88 percent of design for coolant- to gas-flow ratios
from 0 to about 0.10. The range of equivalent turbine speed for the
axial-flow-campressor engine was limited because the noncritical mater-
ial used in the rotor blades prevented uncooled operation at higher
turbine-inlet temperatures.
SYMBOLS
A     area, sq ft
cp    specific heat at constant pressure, Btu/(lb)(R)
f/a   fuel-air ratio
g     acceleration due to gravity, 32.17 ft/sec2
H     lower heating value of fuel, 18,750 Btu/lb
h'    total enthalpy, Btu/lb
J     mechanical equivalent of heat, 778 ft-lb/Btu
M     Mach number
N     rotational speed, rpm
p     static pressure, lb/sq ft
p'    total pressure, lb/sq ft
R     gas constant, ft-lb/(lb)(OR)

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