Understanding and Reduction of Cruise Jet Noise at Aircraft Level

Abstract

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

Under-expanded jet noise prediction using surrogate models based on artificial neural networks

“…The ANN metamodel is here exploited as data-driven model with the aim at representing a dataset built starting from aeroacoustic measurements of a cold jet. The relevance of the physical problem presented in this work lies in the fact that during the cruise phase, due to the combined effect of low external static pressure and required thrust to maintain the flight Mach number, the jet exhausting flow is under-expanded [16,17]. This nozzle condition generates a jet plume with a complex flow pattern characterized by a series of oblique compression and expansion waves that form the so-called shock-cell sequence [18].…”

Azimuthal decomposition of the radiated noise from supersonic shock-containing jets

“…Broadband shock-associated noise (BBSAN) is a high-frequency noise component emanating from shockcontaining supersonic jets. Observed in both military (Vaughn et al, 2018) and civilian aircraft (Huber et al, 2014), it is more prominent in the upstream and sideline directions. BBSAN is produced by the interaction of downstream-travelling turbulent structures with the train of shock-cells in the jet plume (Tam, 1995).…”

Wavepacket modelling of broadband shock-associated noise in supersonic jets

“…Interest in BBSAN remains high for both commercial (Huber et al. 2014) and high-performance military (Vaughn et al. 2018) aircraft.…”

“…At aft angles, the contribution of BBSAN is small compared with turbulent mixing noise (Tam 1995;Viswanathan, Alkislar & Czech 2010). Interest in BBSAN remains high for both commercial (Huber et al 2014) and high-performance military (Vaughn et al 2018) aircraft. This component of supersonic jet noise is the focus of this paper.…”