Installed jet noise is studied by means of a simplified configuration comprising a flat plate in the vicinity of a round jet. The effects of Mach number, jet-plate radial distance, and trailing-edge sweep angle are explored. Acoustic measurements are performed using a traversable 18-microphone azimuthal array, providing pressure data at 360 points on a cylindrical surface surrounding the jet-plate system. Key observations include a decrease, with increasing Mach number, of the relative level of the scattered field in comparison to the uninstalled jet; an exponential dependence of the scattered sound pressure level on the radial jet-plate separation; and considerable sideline noise reductions with increasing sweep angle, with which there is an overall reduction in acoustic efficiency. The measurements are compared with results obtained using a kinematic wavepacket source model, whose radiation is computed in two ways. A TGF for a semi-infinite flat plate is used to provide a low-order approximation of the scattering effect. Use of a more computationally intensive boundary element method provides additional precision. Good agreement between model predictions and experiment, encouraging from the perspective of low-cost prediction strategies, demonstrates that the models comprise the essential sound generation mechanisms.

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This paper is the first part of a series of papers on results obtained in the EXEJET project. EXEJET was a French government-funded program started in 2008 and concluded in 2013, involving 3 partners: Airbus, Onera, Snecma. The project aimed at improving understanding and tools to assess and reduce installed jet noise for modern airliners. Project highlights are the following: Airbus designed and manufactured a swept wing model specifically for wind-tunnel tests at the anechoic facility CEPRA19 -Snecma conceived a large BPR-9 scaled nozzle model with a range of chevron shapes and validated the design methodology -A high-quality experimental flow and noise database was acquired in wind tunnel -Different simulation methods were benchmarked upon this new data. The installation effects of the nozzle under wing are then subject of focus. Significant aeroacoustic installation effect were measured by wing-mounted unsteady pressure sensors, far-field microphones and by Onera three-dimensional source localization array. In the far field, the new wing generated significantly lower levels of background noise in the tunnel compared to previous experience. The installation effects were typically dominant in the low frequency range of jet noise and in the forward arc. Phased array techniques were able to characterize the acoustic installation effects in two dimensions, and quantify them by projection to the far field. In the near field of the powerplant, the unsteady pressure measurements on the wing under-side surface revealed large-scale fluctuations imposed by the jet and spatially coherent. In spite of the presence of pylon and wing, these wavepacket signatures were found qualitatively similar to previous measurements made on coaxial jets from simpler axi-symmetric nozzle. Thanks to the high degree of collaboration between the three partners, EXEJET represents a step beyond the previous common VITAL WP7.2 investigations. The EXEJET database provides a foundation for analysis and validation of future modeling and numerical simulation aiming at quantifying installed jets aeroacoustics. Nomenclature BP RBy-Pass Ratio of an Engine or Nozzle: mass flow ratio between secondary (fan) over primary (core) D mixMixed (or Equivalent) jet diameter (m) JF I Jet-Flap Interaction JW I Jet-Wing Interaction M a Mach number of the flight stream N P R Nozzle Pressure Ratio: total pressure at exhaust over ambient pressure OASP L Overall Sound Pressure Level (dB) OP Operating Point in the test matrix P IV Particle Image Velocimetry SP L Sound Pressure Level (dB) SN R Signal-to-Noise Ratio St Strouhal number T KE Turbulent Kinetic Energy V mix Mixed jet velocity (m/s)Flight stream velocity V P Primary jet exhaust velocity V S Secondary jet exhaust velocity Ψ Polar angle relative to inlet axis Θ Azimuthal angle relative to pylon (180 deg is flyover direction, opposite to the pylon and toward the ground) Dissipation rateThe data analysis presents characteristic distances and velocities in terms of the equivalent mixed jet to allow a better compar...

Within the LINFaN research project, Airbus and Rolls-Royce have jointly investigated the acoustic impact of supersonic jet noise on the fuselage of an Airbus A340 equipped with Rolls-Royce Trent 500 engines in cruise conditions. The main results are presented in this paper. The influence of chevron fan nozzles designed to reduce cruise jet noise on the rear fuselage is investigated. The characterization of both the acoustic field and the aerodynamic flow is carried out. The acoustic data are obtained from a microphone array on the rear fuselage. After specific data de-noising, the acoustic spectra radiated on the fuselage by only the right inner engine are estimated. Beamforming acoustic maps are also computed to localize the jet noise sources. Besides, the supersonic jet flows are characterized by RANS CFD approach. For the baseline round nozzle, the acoustic results show the presence of two distinct broadband shock-associated noise contributions on the fuselage. The first pattern is observed in the far aft section of the fuselage for Strouhal numbers based on the jet mixing diameter and velocity between St = 4 and 6. The other pattern, around St = 1, radiates preferably forward. In addition, the high frequency source is located between 4 and 5 mixed jet diameters past the secondary nozzle exhaust plane, while the low frequency source is located farther downstream between 7 and 8 mixed jet diameters. Shock-associated noise is usually associated with the interaction between shock cells and turbulent shear-layers. We postulate that the high-frequency noise component results from the interaction between the shock-cells in the secondary flow and the inner shear-layer, while the low-frequency component is due to the interaction between shock cells and the outer shear-layer. This interpretation is consistent with two observations. The first observation is a strong modification of the measured high frequency noise when the engine is pushed to high power. At