Investigation of Turbojet Engine Performance at Speeds and Gas Temperatures Above Rated Using Turbine-Blade External Water-Spray Cooling from Stationary Injection Orifices Page: 7 of 33

                                
NACA RM E54G30

PROCEDURE
Engine Operation
The complete range of engine operating conditions reported in this
investigation is presented in table I. The engine was operated without
cooling over a range of speeds and inlet-gas temperatures up to rated at
a constant exhaust-nozzle setting which provided the military rated tail-
pipe-gas temperature of 12650 F. The engine was also operated at rated O
speed over a range of coolant flows and at overspeed with a constant
coolant-to-gas flow ratio. At each overspeed point the exhaust nozzle
was progressively closed from the wide open position until compressor
surge was encountered. Thus a range of turbine inlet-gas temperatures
was obtained at each speed setting. Manual adjustments of the water
supply pressure provided the variations in coolant flow necessary to
maintain an approximately constant coolant-to-gas flow ratio of 0.029.
As in the investigations described in references I and 2, water sprays
were turned on simultaneously with the engine starts to minimize thermal
shock conditions in the blades.
Data Calculations
The calculation procedure for reducing the data obtained in this in-
vestigation to provide spray-cooling-process efficiency, turbine rotor
blade stress level, and turbine and engine performance is as follows.
Spray-cooling efficiency. - The spray-cooling-process efficiency
derived in reference I is expressed as
T 0.75
= K    Tge   ge -Ba1
0.425        w    a
TBa              0.75
3
(All symbols are defined in the appendix.) Equation (1) was evaluated
for every operating point with spray cooling for which sufficient blade
temperature data were available. In equation (1) the average blade tem-
perature, TB, av was taken as the integrated average of the blade midspan
temperatures. The blade root temperatures were not included because of
thermocouple failures at the root position after several runs. The ef-
fective gas temperature, Tg,e (average uncooled blade temperature), was
calculated from turbine inlet conditions by the procedure of reference
3 which utilizes the relation

. . _.