PRINCIPLES OF NAVAL ENGINEERING 



GAS-GENERATOR SECTION 



COMPRESSOR 



COMBUSTION 

 CHAMBER 



SHAFT-L P ELEMENT 



i 



i 



SHAFT-H P ELEMENT STARTER 

 H.P ELEMENT 



TURBINE 



LP ELEMENT 



HP 

 ELEMENT 



LP 

 ELEMENT 



LX3 



POWER TURBINE 

 SECTION 



POWER 

 TURBINE 



LO 



PROPULSION 



POWER 



COUPLING 



147.137 



Figure 23-3.— Schematic diagram showing relationship of 

 parts in twin-spool gas turbine engine. 



atmospheres. Part of the compressed air, called 

 primary air , enters directly into the combustion 

 chamber where it is mixed with the atomized 

 fuel so that the mixture can be ignited and burned. 

 The remainder of the air, called secondary air , 

 is mixed with the gases of combustion. The pur- 

 pose of the secondary air is to cool the combus- 

 tion gases down to the desired turbine inlet 

 temperature. 



Both axial-flow compressors and centrifugal 

 (radial-flow) compressors are currently used 

 in gas turbine engines. There are several pos- 

 sible configurations of these basic types, some 

 of which are in use and some of which are in 

 experimental phases of development. 



In the axial-flow compressor the air is com- 

 pressed as it flows axially along the shaft. 

 An axial-flow compressor of good design may 

 achieve efficiencies in the range of 82 to 88 

 percent at compressor pressure ratios up to 

 8:1. At higher pressure ratios, the efficiency 

 tends to decrease. Axial flow compressors may 



be of the single-spool type, previously illustrated 

 in figures 23-1 and 23-2, or of the twin-spool 

 type, as shown in figure 23-3. The gas turbine 

 engine shown in figure 23-4 has an axial-flow 

 compressor of the single-spool type. Figure 

 23-5 shows an axial-flow single-spool com- 

 pressor removed from its engine. Where twin- 

 spool axial-flow compressors are used, a sepa- 

 rate turbine drives each spool, as shown in 

 figure 23-3. 



The centrifugal (radial-flow) compressor 

 picks up the entering air and accelerates it 

 outward by means of centrifugal force. The 

 centrifugal compressor (fig. 23-6) may achieve 

 efficiencies of 80 to 84 percent at pressure 

 ratios of 2.5 to 4 and efficiencies of 76 to 81 

 percent at pressure ratios of 4 to 10. 



The advantages of the axial-flow compressor 

 include high peak efficiencies; a relatively small 

 frontal area for any given air flow; and only 

 negligible losses between stages, even when 

 a large number of stages are used. The 



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