LTO noise prediction methodology for SST aircraft conceptual design

The new emerging generation of SuperSonic Transport (SST) aircraft demands an enhanced approach for the consideration and analysis of its impact on environment, with the subsequent delivery of relevant Standards and Recommended Practices (SARPs) to make the certification of a supersonic aeroplane possible in the 2020-2025 timeframe. Focusing on noise generated during Landing and Take-Off (LTO) cycle, the presented activities address the development of a methodology aimig at predicting noise levels in the early stages of SST aircraft design process, accounting for noise requirements as a design constraint and supporting a design-to-noise approach. The methodology includes a supersonic aircraft noise model in which overall aircraft noise is predicted as an assembly of major noise sources, each modelled with an individual semi-empirical noise source model based on the equations reported in “Aircraft Noise Prediction Program – Theoretical Manual” published by NASA. Following the aeroacoustics modelling applied in Aircraft NOise Prediction Program (ANOPP), the major LTO noise sources of an SST aircraft have been selected and in addition the noise attenuation due to the propagation in the atmosphere has been considered in accordance with SAE ARP 866 B. The integration of the noise model within the overall methodology framework leads to the prediction of the aircraft noise level. The accuracy of the method in predicting the overall aircraft noise level has been estimated through a dedicated validation with experimental data provided by the Aircraft Noise and Performance (ANP) database for flyover trajectories at different altitudes and thrust ratings. Considering that the goal of the methodology is to predict noise levels for future supersonic aircraft, the only available supersonic aircraft of the ANP, i.e. the Concorde, has been selected as case study. The matching with Noise Power Distance (NPD) curves has been evaluated for maximum A-weighting sound pressure level (LAmax) and Sound Exposure Level (SEL). Ranging from an altitude of about 200 m to 3000 m, the results have showed that the prediction error falls within ±1.5 dBA. Considering that the accuracy is acceptable for applications at a conceptual design level, the overall methodology has been applied to predict noise level at the three certification measuring points (sideline, flyover and approach) defined by ICAO. The results have been reported for each noise source contribution and overall aircraft noise, identifying jet noise as the dominant LTO noise source. The outcome of this research activity demonstrates the capability of the developed methodology in introducing noise evaluations since the early stages of aircraft design. With appropriate improvements in noise source and engine modelling, the methodology can be useful to provide guidelines for the design of future low-noise SST together with operational procedures able to mitigate the LTO noise.