Geared turbofans for large engines

[Astronuc]

Pratt & Whitney aims high for big-jet engine sales
UTX unit touts its geared turbofan engine as a "game changer"

NEW YORK (MarketWatch) -- Pratt & Whitney once dominated the commercial aircraft market with its jet engines, and it intends to do so again with a new engine design the aerospace supplier said will run more quietly and use less fuel than those offered by rivals General Electric Co. and Rolls Royce Group.

A subsidiary of United Technologies Corp. (UTX:United Technologies Corporation) , Pratt & Whitney is developing the first geared turbofan for commercial aircraft, aiming to win contracts at Boeing Co. and EADS Co.'s Airbus unit for the aircraft makers' next-generation narrow-body planes, the widely popular aircraft used for domestic travel.

Unlike typical turbofans, a geared turbofan has a gear box that allows the engine intake fan to turn independently of the low-pressure compressor and turbine, producing the same thrust with 1,500 fewer airfoils, which makes for a quieter ride and could reduce fuel burn by 12%.

"The next-generation single-aisle aircraft demands something different to meet the higher operating costs the world is experiencing," said Tom Pelland, Pratt & Whitney's director of next generation products. "This is our game-changing engine."

Altogether, Pratt & Whitney expects aircraft makers will demand more than 48,000 such engines over a 20-year period beginning in 2013.

. . .

Pratt & Whitney says it's addressed those issues [complex design, longer fan width, extra weight and issues in thermal management] with a new, smaller design for the gear box that uses lighter-weight materials and an improved cooling system. Additionally, it predicts maintenance costs for the engine will be 30% to 40% less because of the reduced number of airfoils.

. . .

Source: CBS MarketWatch

Interesting developments! Certainly - if this works - it will dramatically reduce fuel consumption.

"1,500 fewer airfoils" seems awfully large. But then I haven't counted the blades in current turbine design. I curious as to what the typical blade number is per stage.

 

[kach22i]

Some pictures and diagrams in this SAE article on it.

Link:
http://www.sae.org/aeromag/techinnovations/1298t10.htm

And here:
http://www.flightglobal.com/articles/2006/03/07/205312/gearing-up-again-pratt-whitneys-obsession-with-the-geared.html

My favorite image:
http://www.flug-revue.rotor.com/FRHeft/FRHeft07/FRH0702/FR0702c.htm

The demonstrator produces 133kN of thrust, with a bypass ratio of 11:1. The fan diameter is 203.2cm. “The production version will probably have a diameter of only 190.5 centimetres,” says Saia. To put this in perspective, the fan on the V2500 has a diameter of 161cm. The next step will be to install the eight-stage high-pressure compressor, which Pratt & Whitney is developing jointly with MTU. It is currently undergoing assembly in Munich, where testing is expected to commence shortly after publication of this issue.

At six and a half feet dia., I thought that is slim by today's standards?

 

[Astronuc]

Thanks, kach22i. Interesting picture. The PW.UTC does not list the PW8000 and only refers to the GT (geared turbine) qualitatively.

In the picture, the fan and HP compressor rotates in the opposite direction of the LP compressor.

 

[parsec]

not sure what the forum's policy on sharing books is, but i'll link this anyway

http://parsec.inviscid.com.au/the%20jet%20engine%20gas%20turbine,%20turbojet,%20turbofan%20rolls-royce.pdf

great read. lots of awesome illustrations and diagrams. I'm sure many people here will appreciate this as much as I do (my friends don't :). I can't really think of a more beautiful and elegant machine than the gas turbine.

 

[kach22i]

http://parsec.inviscid.com.au/the%20jet%20engine%20gas%20turbine,%20turbojet,%20turbofan%20rolls-royce.pdf

Nice!

Someone posted a 7-year old Power-Point on something similar a few months ago. It was very confusing about the "electric" parts of the jet at first, not the normal fare.

The Rolls-Royce Trent Engine
http://www.msm.cam.ac.uk/phase-trans/mphil/Trent1/index.htm

 

[FredGarvin]

CONGRATS TO ASTRONUC!

The newest PF Mentor.

Congrats! It's well deserved.

 

[Astronuc]

In a joint program, NASA and Pratt & Whitney demonstrated the noise reduction benefits of an advanced ultra high bypass (UHB) cycle fan concept called the geared turbofan (GTF). This new engine cycle has been designed to obtain peak performance and reduce propulsion noise using a slower, lower-pressure-ratio, geared fan. In wind tunnel tests, the 22-in.-scale model version of the fan demonstrated measured noise levels that were consistent with the predicted levels for a low-speed, low-pressure ratio UHB fan.

Things are moving along.

 

[mgb_phys]

Don't they already have multiple shaft engines alowing the different stages to run at different speeds?

ps. that isn't Rolls-Royce's site, is this a freely available publication or something 'obtained' from RR?

 

[FredGarvin]

Don't they already have multiple shaft engines alowing the different stages to run at different speeds?

Indeed they do. However, the speeds are matched based on aerodynamic and thermodynamic requirements of the components. The kind of speed variations they are talking about necessitate the inclusion of a step down gear assembly. They would never get the speed matching they need to turn the fan as slow as they need to.

 

[Astronuc]

My thinking/conjecture -

I haven't really looked into this, but it seems that one can signficantly vary the proportions of thrust given by the engine exhaust and by-pass fan. More thrust is desirable from the by-pass fan at low altitudes (and take-off and landing) where noise is an issue, as opposed to high altitude where a greater proportion of thrust can come from the jet exhaust.

I think the multiple shaft engines affect the relationship between turbine and compressor, and the by-pass fan is integrated to leading compressor stages.

Correct me if I'm wrong.

 

[mgb_phys]

Am I right in thinking that on a high bypass engine most of the thrust comes form the front stage?
The limit on making the fan bigger is stopping it dragging on the ground.
With this sort of design could you have pairs of fans side-side driven by a single turbine?

 

[FredGarvin]

Am I right in thinking that on a high bypass engine most of the thrust comes form the front stage?
The limit on making the fan bigger is stopping it dragging on the ground.
With this sort of design could you have pairs of fans side-side driven by a single turbine?

You are correct that the majority of the thrust comes from the fan. The limits of size are clearance, as you stated, as well as aerodynamic. The big boys don't want their fan tips going supersonic. We have fan tip speeds that are very high and it brings about a lot of challenges, noise being one of them. Those guys have a much better time with a really big fan that would have slower speeds. A big fan puts out a lot of air.

When you say "side-side" do you mean two fans in parallel or in series?

 

[mgb_phys]

I meant two smaller fans side by side in parallel with only one having a turbine.
(Looking like the twin engine nacelle on something like a B52)

I imagine it's a headache to design an engine to run at high thrust in thick air at takeoff but also cruise efficiently at high altitude. Presumably this design could allow you to change the pressures between the fan and compressor to get a more efficient envolope for different parts of the flight.

ps. Congratulations on the guru award.

 

[FredGarvin]

I meant two smaller fans side by side in parallel with only one having a turbine.
(Looking like the twin engine nacelle on something like a B52)

I imagine it's a headache to design an engine to run at high thrust in thick air at takeoff but also cruise efficiently at high altitude. Presumably this design could allow you to change the pressures between the fan and compressor to get a more efficient envolope for different parts of the flight.

ps. Congratulations on the guru award.

Side by side would be one heck of a big, heavy engine. But I guess since they are playing around with gearboxes for the fans, why not? The design is really based around expected altitude cruise. That is where the majority of the time is spent, so the most dollars operation wise can be saved. Of course, at altitude thrust goes down, but so does all of the bad aspects as well. Altitude is usually your friend. Of course, you do need that take off power for Denver on a hot day.

Wholley molley. I didn't refresh my browser. Thanks. I wouldn't have noticed it unless you pointed it out.

 

[FredGarvin]

I haven't really looked into this, but it seems that one can signficantly vary the proportions of thrust given by the engine exhaust and by-pass fan. More thrust is desirable from the by-pass fan at low altitudes (and take-off and landing) where noise is an issue, as opposed to high altitude where a greater proportion of thrust can come from the jet exhaust.

I think the multiple shaft engines affect the relationship between turbine and compressor, and the by-pass fan is integrated to leading compressor stages.

Correct me if I'm wrong.

You're spot on. The only thing is that, at altitude, you only really would want more of a turbojet engine if you were interested in high speed. That's not a bad assumption considering everyone would want to get to their destination that much quicker. However, all things being equal, I can't see a real benefit that would outweigh the complexity of the engine to change bypass ratios in flight like that.

 

[jaap de vries]

I meant two smaller fans side by side in parallel with only one having a turbine.
(Looking like the twin engine nacelle on something like a B52)

I don't like engines to close together as a consumer because failure of one can easily transfer to the other (Concorde)