Brüel & Kjær Sound & Vibration Measurement A/S

How to certify aero engines


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Aircraft Engine Noise Certification
PowerJet, formed as a joint venture between Russian OAO NPO Saturn & French SNECMA (SAFRAN Group), have designed and built the new SaM146 turbofan engine selected by the Sukhoi Civil Aircraft Company to power its Superjet 100 aircraft family. The Sukhoi Superjet 100 is a medium-haul airliner developed in collaboration with Alenia Aeronautica (Italy), and with consultancy support from Boeing (USA).

With this design went a commitment to the environment. The new engine should incorporate the most stringent noise and emissions standards using state-of-the-art eco-technology – “to meet or exceed current and future regulations”.

Few aviation issues evoke as much interest and emotion as noise. Noise is considered the most important environmental concern for many people who live or work near an airport. Engine manufacturers like PowerJet are, therefore, making huge efforts to reduce their environmental impact and improve cabin comfort.

Noise levels from individual aircraft are restricted by the noise certification requirements given in the Federal Aviation Regulations (FAR) Part 36, and Convention on International Civil Aviation Organization (ICAO) Annex 16. NPO Saturn and Snecma turned to Brüel & Kjær for assistance for noise certification of their new engine. Brüel & Kjær responded with a state-of-the-art noise certification system supporting these regulations.

The PowerJet SaM146 Turbofan

The PowerJet SaM146 is a turbofan engine designed from the ground up to power regional jets. Snecma is in charge of the core engine, control system, transmissions, overall engine integration and flight testing. NPO Saturn is responsible for the components in the low pressure section and engine installation on the Sukhoi Superjet 100 regional aircraft and ground testing - including the noise certification.

Together Snecma and NPO Saturn have built a new Open-Air Test Bench in Poluevo (Russia, Yaroslavl region), to handle certification tests for the SaM146 and other engines. This test rig covers three types of testing: performance, certification operational tests, and noise certification of the propulsion system.

The Engine Noise Certification System
The purpose of the engine noise test is to predict the noise performance of final aircraft in flight for type approval, and to feed engine-specific noise signature such as jet noise, fan noise and pure tones into noise simulation software.

The Brüel & Kjær Static Engine Certification Test system performs data acquisition and analysis for static engine certification testing. The system primarily uses COTS (Commercial Off The Shelf) products, providing a full engine noise measurement and analysis capability. Data acquisition is performed using Brüel & Kjær PULSE acquisition hardware, and real-time and post-processing using Brüel & Kjær's PULSE LabShop software.

The system supports the industry standards and equivalent procedures set out in the certification standards ICAO Annex 16 and FAR 36 (Refs 1 and 2).

The system uses dedicated application-specific software, providing a streamlined workflow, thereby ensuring all required operations are performed to maximum efficiency. The parameter used to assess aircraft noise is the Effective Perceived Noise Level (EPNL) measured in EPN dB. This depends on the annoyance perceived by the ear, the tonal content of the spectrum, and the time during which the aircraft noise remains within 10 dB of the peak noise at the measurement position.

Sound Attenuation Correction for temperature and humidity is in accordance with ARP 866A.

What is Measured?

  • Far-field and near-field microphones provide noise measurements
  • Tacho signals provide engine speed data
  • Data acquisition modules provide acquisition and conditioning of the microphone and speed signals
  • A weather station provides all necessary temperature, wind speed, wind direction, barometric pressure and humidity data
  • An IRIG-B receiver provides time stamping of the data

How is the data handled?

  • Acquisition and Analysis workstations run the software to make the certification noise measurements and analysis
  • Validation workstations provide users remote access to the live data acquired to provide independent validation of the measurement data

With complex measurement set ups like these, getting the measurements right first time is a must! In this specific case, real-time validation of 77 channels up to 25kHz was provided on multiple screens.

Final Reports are generated using pre-defined templates.

NPO Saturn's View

Roman V. Lubimov, General Design Deputy and Director of Building 7 says:

“With the implementation of the SaM146 project, NPO Saturn were faced with the challenge of developing and implementing a complex measurement program using state-of-the-art technology. This included a system for acoustic measurements based on the latest Brüel & Kjær solutions for noise certification testing. With Brüel & Kjær we experienced a company skilled in providing superior hardware and software, acoustic measurement solutions and the professional contractor services needed to supply this unique acoustic measurement system – fully complying with the requirements of the certification standards of ICAO Annex 16 and FAR 36. The presence of Brüel & Kjær’s official representation in Russia had also a positive impact on the quality and timing of this project.” 

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