Safran Undertakes to Make Airplanes Quieter

In April 2017, Safran and the acoustics laboratory of Le Mans University in France inaugurated an industrial research unit specializing 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. Here we discuss the project with Dominique Collin, an eminent acoustics expert at Safran.

What are the issues relating to noise produced by airplanes?
First, it is worth pointing out where these noises actually come from. On the one hand, they come from the propulsion system, as the turbojet noisily expels hot air and the turbofan noisily turns its rotors. On the other hand, the noises come 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 noise pollution. Beyond certification criteria, which are increasingly stringent, we want 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.

What actions have been taken?
In 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. This has reduced the speed at which air is expelled and therefore the turbojet's noise. Today, our efforts focus more on reducing noise produced by the turbofan itself. We are optimizing the shape of rotors with modeling based on the physics of mechanisms that produce noise and improving the efficiency of sound-absorbing materials fitted on the inner linings of nacelles and engine casings.

We believe that the acoustic footprint of airplanes 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.

What about going even further?
The group is involved in demonstration programs like Clean Sky 2, for producing next-generation engines, whether those with an ultra-high bypass ratio or systems like 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 specializing in acoustics materials. These are two key areas of research for Safran. Industrial research units bolster our ties with world-class partners and integrate our issues into doctoral theses undertaken by students. In this way, we can test ideas more quickly and speed up innovation.