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Jet Thrust

  1. Mar 29, 2008 #1
    i am trying to increase the jet engine thrust. today most of the aircrafts are using high bypass ratio turbofan engine. thurbofan engine delivers thrust in two steps
    one: hot exhuast gas
    second : by pass air
    how i have to find the thrust developed by the bypass air?
    how i have to find the thrust developed by the hot exhaust gas?
    GE90- 115B turbofan engine delivers total thrust of 115,000 pounds of thrust, in that how much amount of thrust delivered by the bypass air and by the hot exhaust gas?
  2. jcsd
  3. Mar 29, 2008 #2


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    Welcome to PF, Vincent.
    I believe that Fred Garvin is the guy to answer your questions. Bear in mind, though, that since he designs jets for a living, he won't give you any proprietory information.
  4. Mar 29, 2008 #3


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    I'll defer to Fred on this, but I've looked at lots of articles and not one showed the fraction of thrust from the jet exhaust or bypass flow. I would guess that the exhaust thrust is about 20,000 lbs or so, based on the CFM56 technology.

    I did find some cool stuff though.

    http://www.snecma.com/IMG/pdf/GE90_Anglais-2.pdf [Broken]

    http://www.ihi.co.jp/ihi/file/technologygihou2/10006_1.pdf [Broken]

    See also - http://books.google.com/books?id=VpJEm7cFVE4C&pg=PA26&lpg=PA26&dq=%22jet+engine%22,%22bypass+ratio%22&source=web&ots=z26WF1wyEI&sig=-kAx30UTrX4CaJpK5dAN_hJeMTE&hl=en#PPA21,M1 [Broken]

    Last edited by a moderator: May 3, 2017
  5. Mar 30, 2008 #4

    Thanks for your reply. i have found answer for my question from the NASA Website. please clilk on the link to know about turbofan thrust equation.http://www.grc.nasa.gov/WWW/K-12/airplane/turbfan.html" [Broken]
    Last edited by a moderator: May 3, 2017
  6. Mar 30, 2008 #5


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    That is exactly correct. However, you will not always know the velocities of each stream as required by that page. You may need to delve farther into the thermodynamic relations for the turbofan cycle. You may look to this (usually one starts with known conditions at the inlet and works their way to the back end of the engine):

  7. Mar 30, 2008 #6


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    Just as Fred mentioned, one needs to know the velocities of the jet exhaust and bypass flow (exit).
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