Guillaume Bodard

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.

Statistical Modeling of BBSAN Including Refraction Eects

When operated at o -design conditions, supersonic jets produce BroadBand ShockAssociated Noise (BBSAN). This noise is generated by the interaction of the quasi-periodic shock-cell structure with the large scale turbulence. BBSAN radiation is characterized by multiple frequency humps dominating the jet turbulent mixing noise in the forward quadrant. A semi-analytical prediction method is presented in this paper. BBSAN sources are formally derived from the Linearized Euler Equations and then numerically computed from a calculation of the turbulent mean ow. Moreover, a ray-tracing method is used to account for refraction e ects. Predicted acoustic results are compared with experimental data to assess the model capabilities.