Modellierung der Schallausbreitung in einer inhomogenen Atmosphäre und ihr Einfluss auf binaural synthetisierten Überfluglärm

Abstract

Aircraft noise auralisations are utilized for the development of low-noise aircraft engines or research into the health effects of aircraft noise. Comparatively rarely modelled in them are random atmospheric inhomogeneities, also called turbulence, although they are of relevance for the perception of aircraft noise as they lead to phase and amplitude modulations of the sound propagating through the turbulence. This thesis presents an extension of a method firstly developed by Rietdijk et al. (2017) to model such amplitude and phase fluctuations. The main innovations of the method are: The use of more realistic height-dependent turbulence spectra; the introduction of a time segmentation method to correctly model a moving sound source in the height-dependent turbulence; a parameterisation of the model via simply measurable meteorological quantities. The method - called ’fluctuation model’ in the following - is integrated into an aircraft noise auralisation tool chain of the German Aerospace Center (DLR) and validated via qualitative and quantitative methods. Among other things, the simulated phase and amplitude fluctuations show good agreement with measurements. Furthermore, for the example of an IAE V2527 engine (mounted on an Airbus A320-232), the fluctuation model leads to significantly more realistic results for the psychoacoustic fluctuation strength of the aircraft noise auralisations and to characteristic patterns in spectrograms as they also occur in the spectrograms of the measured aircraft noise. In addition to the fluctuation model, the auralisation tool chain is extended with a postprocessing for binaural synthesis. The binaural auralisations are then examined for their realism via a listening test. Significant differences to specially collected artificial head recordings of aircraft noise are found, which can be attributed, among other things, to the lack of ’liners’ in the noise source modelling of the auralisation. Finally, an application example of the validated auralisation tool chain is presented. The influence of the atmosphere on psychoacoustic metrics of auralised engine noise is investigated, showing a reduction of its loudness, sharpness and perceived annoyance as well as an enhancement of its fluctuation strength by the atmosphere.