Jacques Julliard

Noise-absorption structures and walls constituted thereby

A noise-absorption structure comprising a frame over which a gastight membrane is tensioned, the outside face of the membrane receiving soundwaves, a gas such as air filling the volume defined by the frame and the membrane, and energy-dissipation means housed in the volume, which means are of the laminar gas-flow type, of the electrostatic type, or of the electromagnetic type, and area adjustable or controllable to modify the acoustic impedance of the structure as a function of the characteristics of the noise to be absorbed. The invention is particularly applicable in the aviation industry.

CFM56 Jet Noise Reduction with the Chevron Nozzle

Over the past few years, chevron nozzles have shown promising results to reduce jet noise on moderate to high bypass ratio engines. To support CFM noise reduction packages, GE Aircraft Engines and Snecma Moteurs have performed series of acoustic test campaigns in anechoic wind tunnel jet noise facilities equipped with external flow simulation to assess the jet noise reduction that could be achieved with chevron nozzles on the CFM56 engine. The chevron technology has been applied both to the current nozzle with an internal plug and to a new nozzle design with an external plug. Screening tests have been performed on isolated nozzle configurations at GE Aircraft Engine’s Cell41 scale model acoustic test facility with the most promising configurations tested installed on a partial scale model of an aircraft, in the CEPRA19 anechoic wind tunnel at ONERA. Core and fan chevrons were tested with the pylon for various engine operating conditions and different installed configurations including take-off, cut-back and approach, with appropriate angle of attack and flap settings. The most promising scaled configuration has recently been evaluated during an in flight test campaign with an aircraft equipped with two CFM56 engines. This paper presents the results of tests relative to the jet noise reduction levels achieved at high power setting conditions. Under wing installation effects on jet noise and their impact on the chevron nozzle effectiveness are discussed.

Mixer-Ejector Noise Characteristics with Aerodynamic Performances

A 2D mixer-ejector nozzle device with the acoustically lined wall has been developed for jet noise reduction to achieve the noise level equivalent to ICAO Annex 16 Chapter 3 regulation with minimum thrust losses. In order to investigate flight effects on noise reduction and thrust losses, flight model test were made at the CEPRA19 anechoic wind tunnel in France. Upstream flow conditions of mixer such as velocity profile and temperature profile were simulated as close as the real engine. In this report, some of above experimental test results are presented including noise reduction characteristics by the porous ceramic matrix composites acoustic liner inserted to the ejector shroud and the trend of thrust losses of the mixer ejector nozzle in forward flight. NOMENCLATURE CEPRA19 anechoic wind tunnel CMC acoustic liner EPNL effective perceived noise level [EPNdB]

RACE Aero Acoustic Test Facility: Fan Forward and Rearward 3D Noise Measurements

The RACE aero acoustic test facility located in the Engine Test Center of the French Armament Procurement Agency in the South of Paris, has been set up to investigate modern engine fan aerodynamic performance and noise radiation. The RACE anechoic test bench has been specifically designed to characterize and evaluate the fan noise propagating upstream and downstream a turbofan engine. RACE facility test vehicle, MAESTRO mockup, designed and manufactured by SNECMA in the context of a French national program is a model scale fan representative of a conventional turbofan engine. The far field acoustic measurement device available in the RACE anechoic chamber is unique. A moving rotating and translating acoustic antenna equipped with 31 free field microphones can acquire the acoustic sound pressure field upstream and downstream the test vehicle: the system is thus able to characterize fan forward as well as fan rearward noise. For a given far field antenna full scan, the RACE acoustic acquisition chain can provide up to 1800 narrow band spectra corresponding to one engine operating point. In-duct acoustic measurements can also be carried out on the model scale fan, and in particular an azimuthal mode detection device can be integrated to the machine intake. First aero acoustic tests have been performed in RACE facility last summer with MAESTRO mockup. The main objective of this test campaign was to validate the RACE facility anechoic room versus full scale acoustic measurements realized on a static test bed, and to appraise the attenuation potential of various innovative technologies. Present paper deals with RACE aero acoustic test bench description and focuses on the acoustic measurement capabilities of the anechoic chamber. The calibration results of first acoustic test campaign will be presented as well as the acoustic performance of a lined intake compared to hard wall configuration.

Computation of jet mixing noise for confluent flow

Over the last five years, studies and progress in jet mixing noise prediction coupled with CFD computations have been of large interest at Snecma, especially in the application of High Speed Civil Transport research, where jet noise remain as a major noise contributor. If a good understanding of turbulence mechanisms and mixing processes is needed for further improvements in jet noise reduction, an accurate flow-field description is also searched for, in a way to perform reliable turbulent mixing noise predictions. For the purpose, acoustic and Laser Doppler Velocimetry (L.D.V) measurements were conducted at the CEPRA19 anechoic wind tunnel on axisymmetric confluent flow nozzles operated at high-power conditions, under static and forward flight simulation. Mean flow velocities and turbulent characteristics have been used to validate and calibrate CFD computations performed by the CANARI code used in conjunction with a k-s turbulence model. Calculations were carried out up to 20 diameters downstream of the nozzle exit. The aerodynamic data have then been used as inputs in the MGB code relying on a LighthiUs acoustic analogy for jet noise predictions. In the present study, comparisons between experimental and computational results are shown for both the aerodynamic and acoustic parts. Flight effect and influence of input parameters on flowfield and noise calculation were investigated