and

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