GE and NASA To Begin Wind-Tunnel Testing This Summer of Open Rotor Jet Engine Systems
12 June 2009
| Basic rendering of an open rotor engine. Source: GE. Click to enlarge. |
Following several months refurbishing a special NASA test rig, GE Aviation and NASA this summer will begin a wind-tunnel test program to evaluate counter-rotating fan-blade systems for open rotor jet engine designs. (Earlier post.)
The testing will be conducted throughout 2009 and early 2010 at wind tunnel facilities at NASA’s Glenn Research Center in Cleveland, Ohio. This is not a full engine test, but a component rig test to evaluate sub-scale fan systems using GE’s and NASA’s advanced computational tools and data acquisition systems.
| The refurbished NASA test rig. The subscale composite blades on the rig are baseline designs, reaching back to the open rotor UDF (Unducted Fan) engine of the 1980s. Click to enlarge. |
In the 1980s, GE successfully ground-tested and flew an open-rotor jet engine (the GE36) that demonstrated fuel savings of more than 30% compared with similar-sized, jet engines with conventional, ducted front fan systems. Since then, GE has advanced its computational aero-acoustic analysis tools to better understand and improve open-rotor systems.
The tests mark a new journey for GE and NASA in the world of open rotor technology. These tests will help to tell us how confident we are in meeting the technical challenges of an open-rotor architecture. It’s a journey driven by a need to sharply reduce fuel consumption in future aircraft.
—David Joyce, president of GE Aviation
GE and the Fundamental Aeronautics Program of NASA’s Aeronautics Research Mission Directorate in Washington are jointly funding the program. Snecma (SAFRAN Group) of France, GE’s longtime 50/50 partner in CFM International, a highly successful joint company, will participate with fan blade designs.
For the NASA tests, GE will run two rows of counterrotating fan blades, with 12 blades in the front row and 10 blades in the back row. The composite fan blades are 1/5 subscale in size. They will be tested in simulated flight conditions in Glenn’s low-speed wind tunnel to simulate low-altitude aircraft speeds for acoustic evaluation, and also in Glenn’s high-speed wind tunnel to simulate high-altitude cruise conditions in order to evaluate blade efficiency and performance.
Engine noise is a prime challenge in operating open-rotor engines in a commercial aviation environment.
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| The GE36 unducted fan (open rotor). Click to enlarge. Source: GE |
NASA’s test rig, now refurbished and modernized, was actually used in the 1980s when NASA and GE first tested scale-model, counterrotating fan systems that led to the development of the open rotor GE36 engine. The efficiency from bypass air created by this fan system drove the GE36’s significant fuel savings. As fuel prices fell sharply in the late 1980s and early 1990s, the GE36 was never launched commercially, though it was recognized worldwide as a technology breakthrough.
The first wind-tunnel tests this summer will essentially reenact those 1980s tests. GE and NASA will first run blades of the same design that led to the original GE36 jet engine. This will establish critically important baseline data for GE for flight test correlation because the GE36 in the 1980s flew on Boeing 727 and MD-80 aircraft.
As new and more exotic fan blade designs are run in the wind tunnel, GE and NASA will be able to assess comprehensive aero and acoustic design space in order to better understand how these designs will perform in an actual operating environment.
In total, GE and NASA will run six different sets of blades in the NASA wind tunnels, including five sets of modern blade designs. GE designed and fabricated the scale-model blades at its Cincinnati facility using technical input provided by the GE Corporate Research Center in New York.
Open-rotor jet engine designs are among the longer-term technologies being evaluated for LEAP-X, CFM International’s (GE/Snecma) technology program focusing on future advances for next-generation CFM56 engines. (Earlier post.)
I recall when this revolutionary design came out many years ago & was supposed to be the greatest thing since sliced bread - but then disappeared...ultimately I believe it was the noise which doomed the engine. If they can figure out a way to make it as quiet or quieter than the garden variety jet engine - they might have a winner.
Posted by: ejj | 12 June 2009 at 02:16 PM
Kind of hard to move air at high speed for propulsion and not make noise, it goes with the territory. They may make advances in fuel efficiency for aircraft and come up with renewable fuels soon enough and that is a good start.
Posted by: SJC | 12 June 2009 at 03:01 PM
Actually the jet engien builders have done a considerable amount to quiet their jet engines, including active noise reduction, a la`the Bose approach.
I don't think that would work on open rotor designs, so that stymied their development.
Posted by: ExDemo | 12 June 2009 at 05:07 PM
The closest to this type of engine flying today is on a corporate airplane called a Piaggio P.180 Avanti.
The unique design of this airplane has the 850 hp PT6 turbine engines driving a 5 bladed propeller that is mounted behind the engine on the back of the wing.
It produces a sort of buzzing sound as it goes by. It is a very different sound, sort of irritating because it's not an airplane sound that your ears are used to. I live under the flight pattern of a regional airport, and I can always tell when one of these planes flies over. I think the reason for the sound is because the airflow off the top and bottom of the wing move at different speeds and the prop blades sort of modulate this airflow producing the distinctive sound.
Posted by: Big Al | 12 June 2009 at 07:41 PM
Ah yes! the idea of the old prop/jet revived. I can imagine a 787, which is 20% more efficient fitted with these engine/props and reaching 30% more efficiency.
The down side of course is they don't fly as fast because of the aerodynamic drag.
Posted by: Lad | 13 June 2009 at 07:26 AM
Pratt and GE both worked on this technology in the late 80's early 90's. Why do you think this was given up? Consumer perception of going back to "props" and noise signature issues. Could GE have made advances since the early 90's? sure, but as far as I know and this article seems to state it, this technology has been dormant for a while, other than the computational aero-acoustic analysis tools...
My questions are these:
Is this as a "Hail Mary" pass since Pratt's Geared Turbofan is 3 years away from Type Certification, and they worked on the geared fan for YEARS?
How long will it take GE to have a market ready product from this?
Turbofan's have to do a "blade-out" test, what do you do to insure the blades never liberate from the hub or survive a large bird strike, i.e. geese, since their is no containment ring?
Is this why GE is going "green" since a paradigm changing technology by one of their competitors (Pratt's Geared Turbofan) make further erode their revenue stream of their existing Turbofan engine offerings and a new revenue stream is needed?
Posted by: EGeek | 13 June 2009 at 08:08 AM
The noise problem can be mitigated by locating the prop on the rear part of the aircraft, also using noise cancelation technique, I don't see why it couldn't work in this case since it is already used in the ATR72 with open propellers. Now as for the negative perception of fans, when oil price will be steady over 100, it won't matter. Also most of flight are less than 2 hours.
Posted by: Treehugger | 13 June 2009 at 09:21 AM
I think this design is safer with respect to bird strikes, if they can make it work. The intake is much smaller than a standard engine, lessening the chance of birds getting sucked in. Birds that get shredded by the blades might break some of them, but the blade assemblies will still most likely be able to function after hitting birds.
Posted by: ejj | 13 June 2009 at 09:47 AM
This concept has been at work on the Russian Tupolev Bear long-range bombers for decades. Its speed is slightly slower than its nemesis, the B-52, Mach .75 vs. Mach .9 but much longer range without refueling. Further data can be had by researching the Tu-Bear as to reliability and other aspect of serviceability. (ie. the risk of propeller fallen off and foreign object damage risk).
For an air transport, Mach .75 is fast enough. The main issue is whether petroleum price is high enough or will remain high enough for adaptation of the propfan concept. Inertia and risk aversion will prevent adaptation of any new idea, unless significant benefits exist for doing so.
Posted by: Roger Pham | 13 June 2009 at 01:05 PM
Roger-
The engines used on the Bear are 1950's geared turbo-props. Massive and powerful things though they are, they were probably the best the Russians could do at the time. Boeing and the Air Force considered similar engines for the B-52 but soon realized this was dead-end technology in terms of performance. And these are very different beasts from this GE design which operates at much higher fan speeds. This creates two big engineering problems: suppression of noise and safety (fans letting go with nothing to contain them). Noise will continue to be really important. Look at the expense and care put into the design of the new 787 engines in this regard. You ain't gonna sell too many airplanes if they can only take off and land at research facilities!
Posted by: RD | 14 June 2009 at 11:21 AM
Roger- The Bear was one heck of a noisy bird. The guys manning the DEW line would joke they could hear the bomber coming before the radar saw them coming.
Posted by: ai_vin | 14 June 2009 at 01:09 PM
The most notable and surprising fact is that the Tu-Bear can achieve 400 knots cruise speed vs. the B-52's only 440 kts, using 1950's technology turbine and contralateral gear boxes without swept-back blade tip sections to further reduce tip drags at transonic speeds.
GE's propfan technology is far more advanced, with the blades being directly driven by the turbine stages and not using gear box. By allowing the "stator" to rotate contralaterally behind low-pressure turbine stage, thus acting as another turbine stage, the final turbine stages can rotate at 1/2 the speed and contralaterally to maximize aerodynamic efficiency, without complicated and weighty gear box that is prone to failure, when handling that level of power.
Since 1950's turbojets were very noisy themselves, the noise level of the Tu Bears were quite acceptable at the time they were designed. Modern swept-back-tip blades should allow for some noise reduction, even though still noisier than the ultra-quiet ultra-high-bypass turbofans. But, again, the price of oil will be a powerful deciding factor to whether some extra noise will be tolerated or not. Quietness is a luxury, whereas affordable air travel, to many people, is a necessity.
Posted by: Roger Pham | 14 June 2009 at 10:53 PM