PRINCIPLES OF NAVAL ENGINEERING 



ENTERING 

 STEAM 



FIXED BLADES 



PRESSURE 



VELOCITY 



38.77. 2X 

 Figure 12-9.— Arrangement of fixed and moving 

 blades and pressure-velocity relationships in 

 a reaction turbine. 



which are fastened to the casing rather than 

 to the rotor, serve to direct the steam from 

 one row of moving blades to another. 



As may be seen in figure 12-12, the velocity- 

 compounded impulse turbine has only one pres- 

 sure drop and therefore, by definition, only 

 one stage. This type of velocity- compounded 

 impulse stage is usually called a Curtis stage. 



PRESSURE-COMPOUNDED IMPULSE TUR- 

 BINE,— Another way to increase the efficiency 

 of an impulse turbine is to arrange two or more 

 simple impulse stages in one casing. The casing 

 is internally divided by nozzle diaphragms. The 

 steam leaving the first stage is expanded again 

 through the first nozzle diaphragm, to the sec- 

 ond stage; from the second nozzle diaphragm, 

 to the third stage; and so on. This type of tur- 

 bine is known as a pressure- compounded tur- 

 bine because a pressure drop occurs in each 

 stage. Figure 12-13 shows a pressure-com- 

 pounded impulse turbine with four stages. A 

 pressure- compounded impulse turbine is fre- 

 quently called a Rateau turbine, since it is es- 

 sentially a series of simple impulse (Rateau) 

 stages arranged in sequence in one casing. 



PRESSURE-VELOCITY-COMPOUNDED IM- 

 PULSE TURBINE. -An impulse turbine which 

 consists of one velocity-compounded (Curtis) 

 stage followed by a series of pressure- 



ROTOR 

 MOVING BLADES 



38.771X 

 Figure 12-10.— Section of reaction turbine rotor, 

 showing fixed and moving blades. 



compounded (Rateau) stages is generally re- 

 ferred to as a pressure-velocity-compounded 

 impulse turbine. Turbines of this type are 

 commonly used in the propulsion plants of 

 naval ships. 



PRESSURE - COMPOUNDED REACTION 

 TURBINE. -Because the ideal blade speed in a 

 reaction turbine is so high in relation to the 

 velocity of the entering steam (V^), all reaction 

 turbines arepressure-compounded— thatis, they 

 are so arranged that the pressure drop from 

 inlet to exhaust is divided into many steps by 

 means of alternate rows of fixed and moving 

 blades. The pressure drop in each set of 

 fixed and moving blades (i.e., in each stage) is 

 therefore small, thus causing a lowered steam 

 velocity in all stages and consequently a lowered 

 ideal blade velocity for the turbine as a whole. 



COMBINATION IMPULSE AND REACTION 

 TURBINE.— A combination impulse and reaction 

 turbine employs a velocity-compounded impulse 



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