Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Gas Turbine: Making Rotor as Stator and vice versa

  1. Apr 21, 2014 #1
    Hi,
    Just wondered why the rotor of a gas turbine (generally inside) is not made stationary and the casing (drum that surrounds the rotor) made to rotate...kind of reversed gas turbine...
    One limitation i thought about was the combustion can placement...
    Any other views as to why we don't see gas turbine like that??

    Thanks!
     
  2. jcsd
  3. Apr 22, 2014 #2

    Baluncore

    User Avatar
    Science Advisor

    There is less inertia with a smaller rotating part. It would take longer to spin up a heavy casing.
    The diameter, lubrication and the velocity of the bearing surfaces dictates the geometry at those speeds.
     
  4. Apr 22, 2014 #3
    As dia increases centrifugal forces increases as well.at rpm around 6000 and dia around 900 mm the design is impractical.moreover,casing would be in contact with outside air too.safety issues would also become a hindrance in designing.
     
  5. Apr 22, 2014 #4
    Generator/compressor would also have a rotating casing then...
     
  6. Apr 22, 2014 #5
    thanks all. I understood the above points. Also would that lead to difference in grid compliance code?
     
  7. Apr 22, 2014 #6

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    How would you hang such a beast on an airplane?
     
  8. Apr 22, 2014 #7
    I apologize...forgot to mention that i wanted to know is it possible for industrial gas turbines?
    But it could be fitted on an airplane too...just the casing would be rotating, transferring load to bearing...from bearing to stator shaft(currently our rotor)..this shaft can be clamped at the two ends on a airplane wing...
    kind of tedious but possible...
    Say you have a ball bearing with a rotating shaft, fixed in a stator...earlier shaft was rotating with bearings inner race...now external thing is rotating (bearing outer race rotates, while inner race kept fixed). the stationary shaft coming from bearings inner race can be used to mount the whole thing...atleast on an airplane wing..in a horizontal direction...
     
  9. Apr 22, 2014 #8

    AlephZero

    User Avatar
    Science Advisor
    Homework Helper

    If you can sort out the other mechanical design issues, that would be the easy part.
     
  10. Apr 22, 2014 #9

    Baluncore

    User Avatar
    Science Advisor

    Another problem would be containing the fragments when it disintegrates.
     
  11. Apr 22, 2014 #10

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Still not clear why you would want the casing of a GT to rotate. Run out of things to think about? It's sort of like why can't you make a helicopter where the rotors are fixed and the fuselage rotates.
     
  12. Apr 22, 2014 #11

    AlephZero

    User Avatar
    Science Advisor
    Homework Helper

    That obviously doesm't work for a helicopter, beacuse the fuselage is the wrong shape to generate aerodynamic lift. Maybe the OP is still trying to make something like these "whirling bananas" into a marketable product. (It worked, but no airlines were brave enough to buy it).
    0809.jpg

    That's not an issue, if you can convince the airworthiness regulators that the probability of disintegration is low enough. Containing all the rotating parts in a conventional jet engine design is not feasible (and not attempted) because of the weight of the containment system that would be required.
     
    Last edited: Apr 22, 2014
  13. Apr 22, 2014 #12
    What r we geting at? This is impractical so it is impractical...
    Discuss smthing productive fellows...I posted a thread about impulse turbine plz answer that,I would much appreciate it...
     
  14. Apr 22, 2014 #13

    cjl

    User Avatar

    Well, it wasn't just a matter of airline bravery - it had significant issues meeting noise regulations, and the propulsive efficiency gained was somewhat offset by the fact that the large diameter of the engines doesn't allow them to be easily mounted under the wings like most normal jet engines (which is a more structurally efficient placement for a large aircraft).
     
    Last edited: Apr 22, 2014
  15. Apr 22, 2014 #14

    AlephZero

    User Avatar
    Science Advisor
    Homework Helper

    Indeed - it proved that even a company like GE isn't clever enough to change the laws of physics.

    It's a seductive idea though. All the "big three" engine makers have played with variations on it, with a commercial success rate of 0 out of 3 so far.
     
  16. Apr 22, 2014 #15

    Baluncore

    User Avatar
    Science Advisor

    An industrial gas turbine as referred to in post #7 does not require airworthiness certification.
     
  17. Apr 22, 2014 #16

    AlephZero

    User Avatar
    Science Advisor
    Homework Helper

    In real life many of the components in industrial gas turbines will have airworthiness certificates, because the core of the IGT is identical to the core of an aircraft engine - "identical" as in "built from the exact same part numbers".

    Be that as it may, some of the regulatory design requirements for IGTs can be more severe. For example aircraft engines don't often experience earthquakes while running at full power.
     
  18. Apr 22, 2014 #17

    Baluncore

    User Avatar
    Science Advisor

    But heavy landings and sudden changes of attitude while at precautionary high engine RPM are much more common in aircraft than are industrially significant major earthquakes.

    When it comes to statistical probabilities, the outer casing of gas turbines are always deliberately designed to contain blades that may break from the rotor. More catastrophic failures do occur that escape the containment provided, such as the November 2010, Qantas Flight 32, engine failure.
     
  19. Apr 23, 2014 #18
    Hi..
    I didn't knew that it was impractical..that's why I asked the question...
    If a thing isn't built in a particular way..there are always reasons...just wanted to know..
     
    Last edited: Apr 23, 2014
  20. Apr 24, 2014 #19
    There's a company developing gas turbines with an internal normal rotor and the casing fitted with blades also rotating but in the opposite direction, this does away with the need for interstate guide vanes making the engine shorter and more efficient, I haven't heard recently what progress they are making.
     
  21. Apr 25, 2014 #20
    Ya..thats good info...thanks again!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook