|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.
|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.)