Aircraft Noise Prediction: from Trajectory to Synthesis

Doctoral thesis, 2024

The issue of aircraft noise gained significant attention with the introduction of turbojets in commercial flights during the early 1960s. This led to the establishment of a series of standards and regulations that contributed to the development of quieter aircraft and the reduction in community noise impact. Since then, the regulations have continuously evolved, with ongoing efforts to mitigate aircraft noise focusing on advancements in aircraft and engine design and on more efficient flight procedures.
An important factor in making effective design choices in these efforts is the early noise impact assessment, ideally not only through conventional metrics but also through perception-based evaluation. One of the objectives of this work was to develop an aircraft noise prediction framework, capable of performing such assessments. At its core, this framework consists of trajectory modelling with aircraft and engine design and performance evaluation, source noise prediction, and propagation to a receiver. Incorporating the calculation of noise contours provided a more accurate representation of community noise impact across entire areas, facilitating the evaluation of noise from various scenarios. Nevertheless, the implemented conventional
metrics could not fully capture the sound characteristics and perceived annoyance. To address this limitation, auralization was used to synthesize the predicted noise into audible sounds, providing a deeper understanding of the perceived noise. This comprehensive framework, starting with trajectory modelling and concluding with noise synthesis, facilitated a thorough assessment of different scenarios and their noise impact.
The selected scenarios primarily focused on flight path management, but the possibility of noise reduction at the source during the early design stages of conventional aircraft was also explored. Through a system-level analysis, new propulsion system designs were established indicating improvement in noise and NOx emissions, for a minimum penalty in fuel consumption. Additional mitigation possibilities were explored through the operational aspect, aiming to establish quieter procedures, particularly during approach, through procedure design and optimization. The operational aspect was further investigated using experimental data to examine how variations in flight parameters influence noise across different approach configurations.
In most of the aforementioned studies, interdependencies between noise, CO2, and non-CO2 emissions were assessed, highlighting the importance of considering trade-offs to avoid counteracting the benefits of noise mitigation with adverse effects on air quality. Overall, it was demonstrated that significant reduction can be achieved by designing feasible procedures within the current regulatory frameworks.