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MARINE  GAS  TURBINES
Turbine operating theory

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Figure 6-5.—Newton’s third law of motion. cruising   range   and   reliability,   but   they   have a   disadvantage   when   used   in   antisubmarine warfare. Their low-frequency sounds travel great distances   through   water,   making   them   easily detected  by  passive  sonar.  Steam  turbines  have been combined with gas turbines in the steam and gas  turbine  propulsion  (COSAG)  configuration to  reduce  low-frequency  sound.  This  configura- tion requires more personnel to operate and does not  have  the  range  of  the  diesel  combinations. Another configuration, the combined gas turbine or  gas  turbine  (COGOG)  has  also  been  successful. The  British  County  class  destroyers  use  the  4,500 hp Tyne gas turbine engine for cruising and the 28,000  hp  Rolls  Royce  Olympus  engine  for  high speed. The U.S. Navy entered the marine gas turbine field  with  the  Asheville  class  patrol  gunboats. These ships have the CODOG configuration, with two  diesel  engines  for  cruising,  and  a  General Electric LM 1500 gas turbine for operating at high speed.  As  a  result  of  the  increasing  reliability  and efficiency  of  new  gas  turbine  deigns, has   now   designed   and   is   building destroyers, and frigates that are entirely by marine gas turbine engines. BASIC  ENGINE  THEORY the Navy cruisers, propelled Newton’s third law of motion states that for every  action  there  is  an  equal  and  opposite reaction. If you have ever fired a shotgun and felt the  recoil,  you  have  experienced  an  example  of action-reaction   (fig.   6-5).   This   law   of   motion is  demonstrated  in  a  gas  turbine  by  hot  and expanding gases striking the turbine wheel (action) and  causing  the  wheel  to  rotate  (reaction). Figure 6-6.—Turbine operating theory. OPERATING  PRINCIPLES Figure 6-6 demonstrates the basic principles of  gas  turbine  operation. A  blown-up  balloon  (fig.  6-6,  view  A)  does nothing until the trapped air is released. The air escaping  rearward  (fig.  6-6,  view  B)  causes  the balloon  to  move  forward  (Newton’s  third  law). If we could keep the balloon full of air (fig. 6-6, view  C),  the  balloon  would  continue  to  move forward. If a fan or pinwheel is placed in the air stream (fig. 6-6, view D), the pressure energy and velocity energy will rotate the fan and it can then be used to  do  work. 6-3






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