Aircraft noise immission modeling

This contribution to the CEAS special edition Aircraft Noise Generation and Assessment focuses on the simulation of the aircraft noise immission, i.e., the aircraft noise received on the ground. This process includes two steps, the description of the sound emission by the aircraft and the modeling of the sound propagation through the atmosphere. An overview is provided on how aircraft noise immission can be described and assessed by noise descriptors. These quantities can be derived from measurable and computable quantities like maximum sound levels, time-integrated sound levels and the number of aircraft movements. Moreover, a generation of novel noise indices which relate human reactions to noise is presented. Fundamentals of aircraft noise modeling are explained. First, this includes a classification of aircraft noise models into best practice and scientific models and their applicability to the noise mitigation measures described by ICAO’s Balanced Approach to Aircraft Noise Management. Furthermore, the overall workflow of a noise modeling task is explained as well the special role of noise model databases and the simulation of aircraft flight paths. The most common methods used to describe the sound propagation process through the atmosphere are introduced. This covers the modeling of the fundamental propagation effects which are used by all noise model types as well as a description of propagation effects which are of importance only for special modeling tasks and which normally require sophisticated physical approaches. The fundamental difference between best practice and scientific aircraft noise models—i.e., the source modeling—is described in detail thereafter. Best practice models are based on a simple source description. Moreover, a common approach is to combine emission and propagation using pre-calculated noise–power–distance tables. In contrast, scientific models are of multi-source type, i.e., they differentiate between particular noise-generating mechanisms—at least between engine noise and aerodynamic noise. This model type always requires a time step-based flightpath description, whereas the best practice models usually are based on a flightpath description by longer segments. Finally, the selected application examples are presented for both model categories. This covers the range from noise zoning over what-if studies for noise mitigation measures or definition of noise abatement flight procedures up to the modeling of noise reduction measures at the source. Finally, the application of scientific models in the aircraft design phase is explained.