parapente
Topic Author
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Contra Rotating Cores And Rotors

Wed Apr 28, 2010 8:57 am

Question to the engine experts.

Contrarotating cores has been the latest big step in commercial engine design.Both GE and Rolls (and P&W) accept that contra rotating fans or "Open Rotors" is a must for a further leap in efficiency.

Question.Could one take the 2 contra rotating shafts on the core to directly power the 2 contra rotating sets of blades (shrouded or not ) and thus eliminate all the complicated gearing that would otherwise be necessary?

GE has 2 shafts and RR could pick 2 of 3.

Prior to contra rotating cores there was no option.I just wondered whether this new technology might well fit in with the next leap forward at the "front end"?
 
Fly2HMO
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RE: Contra Rotating Cores And Rotors

Wed Apr 28, 2010 9:14 am

Quoting parapente (Thread starter):

Question.Could one take the 2 contra rotating shafts on the core to directly power the 2 contra rotating sets of blades (shrouded or not ) and thus eliminate all the complicated gearing that would otherwise be necessary?

Doubt it. The velocities and pressures inside the core will be very different than those on the exterior where the rotors would be. Not having any gearing would restrict the core to run at the speed the rotors will be at, and vice versa.

If anything you could have an additional independent shaft for a power turbine type arrangement like you'd have in a PT6 turboprop. That way the gas generator could run at its optimal speed and the power turbine/rotors at their optimum speed. Come to think of it, a shaft wouldn't really be necessary, the rotors could be connected directly to the power turbine via the turbine's outer disk. IIRC that has been done before.

Hope that makes sense. It's 230AM   

[Edited 2010-04-28 02:15:50]
 
DH106
Posts: 595
Joined: Wed Jun 15, 2005 5:32 pm

RE: Contra Rotating Cores And Rotors

Wed Apr 28, 2010 10:19 am

And there's the physical engineering problem of extending the outer shaft forward of the LP compressor / fan which sits on the inner most shaft.
...I watched c-beams glitter in the dark near the Tanhauser Gate....
 
tdscanuck
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RE: Contra Rotating Cores And Rotors

Wed Apr 28, 2010 12:56 pm

Quoting parapente (Thread starter):
Both GE and Rolls (and P&W) accept that contra rotating fans or "Open Rotors" is a must for a further leap in efficiency.

How do you figure? P&W's GTF doesn't use contra-rotating fans or open rotors.

Quoting parapente (Thread starter):
Question.Could one take the 2 contra rotating shafts on the core to directly power the 2 contra rotating sets of blades (shrouded or not ) and thus eliminate all the complicated gearing that would otherwise be necessary?

In theory, yes. However, as Fly2HMO pointed out, you'd have a terrible mismatch between flow conditions and I don't think it's likely that this configuration would ever be the optimal one.

Quoting Fly2HMO (Reply 1):
Come to think of it, a shaft wouldn't really be necessary, the rotors could be connected directly to the power turbine via the turbine's outer disk. IIRC that has been done before.

I'm pretty sure that GE's open rotor concept test engine did this.

Tom.
 
Fly2HMO
Posts: 7207
Joined: Sat Jan 24, 2004 12:14 pm

RE: Contra Rotating Cores And Rotors

Wed Apr 28, 2010 5:53 pm

Quoting tdscanuck (Reply 3):
I'm pretty sure that GE's open rotor concept test engine did this.

Yeah it seems most designs are based on that principle.



By the way, are there any videos showing the sound these things make? All I know is that they were infamously loud.


EDIT: Found one, can barely here it though: http://www.youtube.com/watch?v=zxVAaIsfPIY

Also interesting to note, the $.50 price for Jet-A at the time   

[Edited 2010-04-28 11:03:06]
 
A342
Posts: 4017
Joined: Sun Jul 31, 2005 11:05 pm

RE: Contra Rotating Cores And Rotors

Wed Apr 28, 2010 8:51 pm

Quoting Fly2HMO (Reply 4):
Also interesting to note, the $.50 price for Jet-A at the time

Was that per gallon?
Exceptions confirm the rule.
 
Fly2HMO
Posts: 7207
Joined: Sat Jan 24, 2004 12:14 pm

RE: Contra Rotating Cores And Rotors

Wed Apr 28, 2010 9:29 pm

Quoting A342 (Reply 5):
Was that per gallon?

Yup. At 4:02 in the video they mention that's what it cost at the time the video was made.
 
parapente
Topic Author
Posts: 1345
Joined: Tue Mar 28, 2006 10:42 pm

RE: Contra Rotating Cores And Rotors

Fri Apr 30, 2010 8:34 pm

Thanks guys really interesting.It's a hard subject (i find) to understand at the required depth.

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