Snecma is about to carry out further tests on a one-fifth scale model of an open rotor engine, in a research and technology effort that epitomizes how laborious developing a new commercial engine concept can be. The concept, based on counter-rotating high-speed propellers, may not find itself in service before 2025, but the objective is to cut fuel burn by 25 to 30 percent compared to the CFM56 (Snecma’s current narrowbody engine, produced in conjunction with GE).
A new series of evaluations are planned to start this month at the Onera S1 windtunnel in Modane, France. “This time it will be a high-speed test, since we want to demonstrate the engine’s potential for reducing fuel consumption,” propeller module manager Marc Doussinault explained.
The previous series of tests, which lasted two weeks in July, focused on the engine’s low-speed aerodynamics and acoustics. The French engine maker’s engineers checked out several propeller pairs. In the S1 wind tunnel they used the Hera testbed, aimed at maturing the design of the propellers. In two series of tests, one used the baseline propeller pair, which had already been tested, and the other was a new configuration. The latter arrangement allows the propellers to rotate at different speeds, “giving the engine greater operating freedom and enhancing both aeroacoustic and aerodynamic performance,” according to Snecma (Stand 1145).
Test results validated design software programs. Moreover, they helped explain the physical phenomena involved in reducing the usually dreadful noise of counter-rotating propellers. “We have demonstrated that we can meet the new noise standards,” Doussinault said.
A major step in open-rotor development is to occur in 2015 in Istres, southeast France, where full-scale propellers will be tested. The project will study blades made of 3-D-woven composites, like those of CFM’s Leap turbofan, which therefore means that blade design has to be frozen shortly. “We will start manufacturing the molds in early 2014,” Doussinault said.
Aerospace research center Onera also emphasized its role in the effort. This included “innovative and even revolutionary approaches,” Patrick Wagner, director of computing, engineering and testing facilities, told AIN. Onera is now working on a more advanced testbed, dubbed Z49, which will be able to accommodate an open-rotor model and accompanying fuselage, wing or empennage model. In fact, Onera has already begun the validation phase of Z49 in S1, and it is understood that Snecma’s open-rotor model was used for this purpose.