programme this summer to evaluate open-rotor jet engines

The refurbished NASA test rig (photo: GE) Following the refurbishment of a special test rig at NASA’s Glenn Research Center in Cleveland, Ohio, engine manufacturer GE Aviation and NASA will begin wind-tunnel testing of counter-rotating fan-blade systems for open-rotor jet engine designs this summer. The open-rotor engine has been touted by both GE and rival Rolls-Royce as a possible next-generation engine for narrowbody aircraft because of its potential for substantial reductions in fuel consumption and emissions of CO2 and NOx. However, the prime challenge for them both is to arrest the significant increase in engine noise levels posed by the open design. NASA’s test rig was actually used in the 1980s when NASA and GE first tested scale-model, counter-rotating fan systems that led to the development of the open-rotor GE36 engine. GE successfully ground-tested and flew an open-rotor jet engine – then called an unducted fan (UDF) – that demonstrated fuel savings of more than 30% compared to similar-sized, conventional engines. The design was prompted by a surge in the oil price at the time but was shelved once the price fell back. Although a similar scenario has been repeated with the price of crude oil falling from a peak of nearly $150 per barrel to nearer $30 earlier this year, circumstances are different this time round. The price has now risen sharply back to around $70 and could go higher still once the global recession begins to play itself out and, as important, the environmental imperative is so much stronger now than it was over 20 years ago. GE says it has dramatically advanced its computational aero-acoustic analysis tools since then to better understand and improve open-rotor systems. The manufacturer stresses the programme will not involve full engine testing but will be a component rig test to evaluate subscale fan systems. GE and the Fundamental Aeronautics Program of NASA’s Aeronautics Research Mission Directorate in Washington are jointly funding the testing, with Snecma of France – GE’s partner in CFM International – participating with fan blade designs. For the NASA testing, which will essentially re-enact the 1980s tests, GE will run two rows of counter-rotating fan blades, with 12 blades in the front row and 10 blades in the back row. As new and more exotic fan blade designs are run in the wind tunnel, GE and NASA say they will be able to better understand how these designs will perform in an actual operating environment. “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,” said David Joyce, President of GE Aviation. Open-rotor jet engine designs are among the longer-term technologies being evaluated for LEAP-X, CFM International’s technology programme focusing on future advances for next-generation CFM56 engines.