Hush! Safran to make aircraft quieter
In April 2017, Safran and the acoustics laboratory of Le Mans University in France inaugurated an industrial research unit specialising in innovative acoustics materials for the aerospace industry. This research partnership is part of the group’s wider efforts to reduce levels of noise produced by airplanes. Dominique Collin, an eminent acoustics expert at Safran details the project:
First, it is worth pointing out where this noise actually comes from. On the one hand, it comes from the propulsion system, as the turbojet noisily expels hot air and the turbofan noisily turns its rotors. On the other hand, the noise comes from turbulence in the flow of air over the airplane’s structure: landing gear, propelling nozzle, flaps, etc. These are the sounds that cause “noise pollution” for residents around airports. Safran is doing all it can to reduce this. Beyond certification criteria, which are increasingly stringent, Safran wants to go further in responding to the specific requirements of certain airports. These are even more demanding than regulations. All these efforts form part of the objectives of ACARE1: halving the noise heard by 2020 than in 2000 and 65% less by 2050.
In aero- engines, an increase in the bypass ratio (the relationship between the flow of hot air the flow of cold air), achieved by widening the turbofan’s diameter has greatly contributed to progress made over the past 40 years, and has reduced the speed at which air is expelled and therefore the turbojet’s noise. Today, efforts focus more on reducing noise produced by the turbofan itself. The company is optimising the shape of rotors with modeling based on the physics of mechanism that produce noise and improving the efficiency of soundabsorbing materials fitted on the inner linings of nacelles and engine casings. Safran believes that the acoustic footprint of aircraft on the ground has been reduced by 75% overall in four decades. With the CFM56, introduced on the market in the 1990s, and the new LEAP engine, an improvement of 12 decibels on average has been achieved.
The group is involved in demonstration programmes like Clean Sky 2, for producing next-generation engines, whether those with an ultra-high bypass ratio or systems like the Open Rotor. It also supports basic research, particularly through industrial research units. As such, following ADOPSYS2 for aeroacoustics, Safran is co- funding the MACIA3 research unit specialising in acoustics materials. These are two key areas of research for Safran. Industrial research units bolster their ties with partners and integrate issues into doctoral theses undertaken by students. In this manner the company can test ideas more quickly and speed up innovation.