Jerome Huber

Jet Noise Assessment and Sensitivity at Aircraft Level

This paper proposes an investigation of the assessment of jet noise and its reduction at aircraft level for the community standards of modern airliners. A sensitivity study is conducted on jet mixing noise using a well-established overall noise evaluation process. The study shows how noise generation, propagation effects and psychoacoustic factors combine to define the frequency and angle ranges for which jet noise impacts most the noise levels measured at the ground. These most sensitive zones are between Strouhal 0.8 and 3 and over a potentially large range of polar angles. This correlates well with the distribution of peak noisiness at the ground due to the jet. In a second step, a generic jet noise reduction technology is modeled in terms of its far-field acoustics. The impact of the generic technology is evaluated parametrically. Although global noise reductions are often project-specific, some trends are discerned and related to the set of circumstances in the evaluation. The importance of low-frequency noise reduction reaching up to Strouhals 3 to 5 is highlighted.

Large-Scale Jet Noise Testing, Reduction and Methods Validation "EXEJET": 1. Project Overview and Focus on Installation

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.

Understanding and Reduction of Cruise Jet Noise at Model and Full Scale

This paper presents an investigation into supersonic jet noise of commercial aircraft in cruise conditions. It draws on results from the LINFaN research project, which was conducted jointly by Airbus and Rolls-Royce. The main objective of this programme is to study and control the cruise noise levels. It has allowed us to gain a deeper understanding of jet noise sources of modern high-bypass-ratio engine nozzles during cruise, and their impact on the fuselage skin. The study includes dedicated flight tests to measure noise on an Airbus A340 with Rolls-Royce Trent 500 engines, jet noise model-scale tests in a transonic wind tunnel and analytical studies on shock-associated noise using CFD. From the flight tests, jet noise spectra are obtained over the rear part of the fuselage, for different engine conditions and for different fan nozzle chevrons, and acoustic maps of jet noise sources are obtained using a beamforming technique. Model-scale tests have also been performed, which allow us to measure jet noise at representative cruise conditions. Many different nozzle designs can be tested over a full range of operating conditions and flight Mach numbers. RANS CFD methods are used to analyze the supersonic jet behaviour in cruise conditions. The investigation methodology is applied to two distinct dual-stream nozzles, starting with the Rolls-Royce Trent 500 nozzle. In flight, the presence of two distinct broadband shock-associated noise contributions are found on the fuselage, and effects of nozzle operating conditions are highlighted. The flight tests, wind-tunnel tests and flowfield analysis all show that chevrons on the fan nozzle modify significantly the near-field jet noise. For the Trent 500 engine, immersive fan chevrons reduce lowand high-frequency shock noise by as much as 7 dB on the peak level, and also increase shock-associated noise frequencies. The impact of chevrons on shock noise is found to be dependent on the engine

Aircraft Noise Impact Under Diverse Weather Conditions

Weather affects both the performance of aircraft and the propagation of noise. Thus, the impact of aircraft noise on communities surrounding airports can vary with changes in the weather at or around an airport. This paper explores the magnitude of these effects for aircraft departing from Runway 4R at Boston Logan International Airport, and illustrates how the noise impact can be significantly reduced by changing the departure procedure to capitalize on changes in the weather.

Characterization of Installation Effects for HBPR Engine, Part 4: Assessment of Jet Acoustics

This paper is the last part of a series of four papers characterizing the installation eects of a typical high bypass ratio engine jet using numerical simulations and particle image velocimetry. The global objectives are an improved understanding of the link between the jet ows and the generated noise, the validation of methods for computing the aerodynamic eld and the noise sources for industrial congurations, and the assessment of the benets

Effects of meteorology on predicted levels of aircraft noise

Calculation of average noise (e.g., Ldn) around airports generally ignores the effects of atmospheric gradients as these effects are assumed to average out over the course of a year. The validity of this assumption was tested through a numerical study using the aircraft noise simulation model NMSIM. Specifically, NMSIM was extended to account for three‐dimensional refraction by wind and temperature gradients, plus refraction and scattering into shadow zones, as well as ground impedance effect. Five years of meteorological data at a number of airport locations was obtained, and divided into hourly conditions. A nominal airport, based on a major air carrier airport, was defined. NMSIM was run for hourly operations and weather conditions at each airport location. The resultant Ldn contours were compared to each other by season and location, and also to contours computed for the baseline assumption of no gradients. [Work supported by NASA Langley Research Center.]