Chapter 23. -GAS TURBINE 



GAS -GENERATOR SECTION 



STARTER 



COMBUSTION 

 CHAMBER 



COMPRESSOR 



SHAFT 



GAS-GENERATOR 

 TURBINE 



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 Rgure 23-2.— Schematic diagram showing relationship of parts in split-shaft gas turbine engine. 



POWER TURBINE SECTION 



POWER 

 TURBINE 



SHAFT 



PROPULSION 



POWER 



COUPLING 



element. Like the split-shaft type, the twin- 

 spool gas turbine engine is usually divided into 

 a gas-generator section and a power turbine 

 section. However, some twin- spool gas turbine 

 engines are so arranged that the low pressure 

 turbine element drives the low pressure com- 

 pressor element and the power output shaft. 



The basic cycle of the gas turbine engine 

 is one of isentropic compression, constant- 

 pressure heat addition, isentropic expansion, 

 and constant-pressure heat rejection. As the 

 hot combustion gases are expanded through the 

 turbine, converting thermal energy into mechan- 

 ical work, some of the turbine work is used to 

 drive the compressor and the remainder is used 

 to drive the load. The power output from the 

 turbine is steady and continuous and, after the 

 initial start, self-sustaining. 



Although this chapter deals only with gas 

 turbine engines which operate on the simple 

 open cycle, it should be mentioned that other 

 cycles are also of interest to designers of gas 

 turbine engines. Among the cycles that have 

 been considered (and to some extent used) are 

 the closed cycle, the semi-open cycle, and 



various modifications of the simple open cycle. 

 In one such modification, known as the regen - 

 erated open cycle , the hot exhaust gases from the 

 turbine are passed through a heat exchanger in 

 which they give up some heat to the air between 

 the compressor discharge and the inlet to the 

 combustion chamber. The utilization of this heat 

 decreases the amount of fuel required and there- 

 by increases the efficiency of the cycle. 



FUNCTIONS OF COMPONENTS 



As we have seen, the three major compo- 

 nents of a gas turbine engine are the compres- 

 sor, the combustion chamber, and the turbine. 

 In addition, the engine requiresanumber of other 

 components, accessories, and systems in order 

 to operate as a complete unit. The functions of 

 the gas turbine engine components are described 

 in the following sections. 



Compressor 



The compressor takes in atmospheric air 

 and compresses it to a pressure of several 



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