sonAIR

sonAIR is an aircraft noise calculation model that has been developed at the la-boratory for Acoustics / Noise Control of Empa between 2012 and 2016 and which is being constantly actualized. The model comprises of a source model describing in detail the sound emission and directivity as a function of flight configuration (power setting and aeroplane configuration, i.e., flaps, slats and landing gear). The source model is combined with the highly developed sound propagation model sonX of Empa. Individual flights are simulated according to a time-step procedure. The resulting aircraft noise calculation model is able to reliably predict noises levels even in greater distances from the airport. In addition, the model can be applied for the development of noise abatement operational procedures and thus con-tribute to a minimization of entailed annoyance during the day, sleep disturbance during the night, and finally of noise-induced costs.

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Exemplarily simulation of an Airbus A320 along its flight path
Acoustical measurements and aircraft parameter

An extensive acoustic measurement of real air traffic in the close vicinity and at large distances of Zurich airport was carried out in the years 2013 and 2014. The measure-ments covered the major large aircraft types operating in Switzerland. In total 2‘600 overflights in the close range of the airport, each recorded on eight different micro-phone locations, and 11‘000 overflights in the far range of the airport at ten different locations from Pfannenstiel to Winterthur as well as Bellikon (Aargau) have been rec-orded.
To develop the sound source model, cockpit data – which were available in this pro-ject for Swiss and Edelweiss flights– yield an ideal data basis to connect the acoustic measurements with the actual flight condition. For aircraft of other airline companies, an optical tracking system was used in the close vicinity of the airport to complement radar data. Further, a special analysis procedure to determine the low compressor speed of starting and landing aircraft was applied.

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Measurement of landings on runway 14 in the close range of Zurich airport
Source Model

To establish the source model the measured spectra were propagated back to the source and connected to the corresponding flight conditions. Thereby, propagation time, the Doppler shift (frequency as well as intensity) and also all important propaga-tion phenomena such as the ground effect and vertical stratification of the atmosphere in terms of temperature, humidity, wind and air pressure were taken into account.
In the dissertation of C. Zellmann a method was developed to divide the empirical da-ta into two separated source models, namely the engine and airframe noise model. The most important parameters for both approaches were identified and applied to each aircraft type. Finally, the energetic sum of the engine and airframe noise model adds up to the directional sound power level as a function of the flight configuration.

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Overview of the separated sound source model and its parameter (Lw- sound power level)
Simulation
For the simulation of aircraft noise a time-step method is applied. Single flights are represented in a fine temporal resolution with the current position and orientation as well as thrust setting and configuration as input parameters. This approach allows a detailed analysis of the sound exposure at any point of interest, yielding not only spectral information but also level-time histories. Long-term exposure is obtained by superposing numerous flights. Based on these results comparisons with noise limits or statistics on the number of affected people (high annoyance, sleep disturbance) can be derived.
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Acoustic footprint showing an LASmax distribution of an A330-300 take-off on runway 16 of Zurich airport Specific source and propagation effects are labeled.

Status
sonAIR was developed as a research tool and will constantly be further developed for that purpose. In parallel an implementation of sonAIR in a geographic information system GIS is currently done in collaboration with the company n-Sphere AG. This tool shall in the future be made available for a broader group of users.

Funding
sonAIR was funded within the Special Financing of Civil Aviation by the Federal Office of Civil Aviation (FOCA). Additional funding was provided by Empa, Flughafen Zürich AG, Aéroport International de Genève (AIG), Office of Transport of the Canton of Zur-ich (AFV), as well as skyguide within the framework of CHIPS. Partners within the initial sonAIR project were the companies SciTracks GmbH for the mobile optical flight path tracking system and BeSB GmbH Berlin for the determination of the low compressor speed. Funded by the Federal Office for the Environment (FOEN) and in collaboration with the company n-Sphere AG, the new aircraft noise calculation model is being im-plemented in a geographic information system GIS.

References:
Zellmann C, Schäffer B, Wunderli JM, Isermann U, Paschereit CO (2017).
„An Aircraft Noise Emission Model Accounting for Aircraft Flight Parameters”, Journal of Air-craft, accepted on 17/7/9 (2017)
Zellmann C, Wunderli JM, Paschereit CO (2016). „The sonAIR sound source model: spectral three-dimensional directivity patterns in dependency of the flight condition”, INTER-NOISE 2016 - 45th International Congress on Noise Control Engineering: Towards a Quieter Future; Hamburg, p. 786-94.
Zellmann C, Wunderli JM (2014). „Influence of the atmospheric stratification on the sound propagation of single flights”, INTER-NOISE 2014 - 43rd International Congress on Noise Control Engineering: Improving the World Through Noise Control; Melbourne.
Zellmann, C., J. M. Wunderli and B. Schäffer (2013). SonAIR - Data acquisition for a next genera-tion aircraft noise simulation model. 42nd International Congress and Exposition on Noise Con-trol Engineering 2013, INTER-NOISE 2013: Noise Control for Quality of Life.
Schäffer, B., C. Zellmann, W. Krebs, S. Plüss, K. Eggenschwiler, R. Bütikofer and J. M. Wunderli (2012). Sound source data for aircraft noise calculations – state of the art and future challenges. Proceedings of Euronoise 2012, Ninth European Conference on Noise Control, Prague, Czech Republic.