Sound evaluation based on listening experiments is very costly and time-consuming. Alternatively,... more Sound evaluation based on listening experiments is very costly and time-consuming. Alternatively, the sounds under evaluation can be compared using psychoacoustic metrics, under the hypothesis that sounds that differ by more than one just-noticeable difference (JND) are perceived as significantly different from each other. Wellestablished psychoacoustic metrics are obtained from models of loudness, sharpness, roughness, fluctuation strength, and tonality. In the present study, we use these psychoacoustic models to analyse a selection of aircraft flyovers and train pass-by sounds, as well as fluctuating sounds obtained from resonances of a rotating flexible tube. In addition to the description of the adopted model implementation of each psychoacoustic metric, our discussion focuses on technical and practical aspects including (1) the dependency of the results on the appropriate sound and model calibration, and (2) how to interpret the results based on reported JNDs from the literature. We reflect on how much we can rely on a specific model implementation considering the status of the metric-standardised (or not), accessibility to algorithms and to their validation results (or not)-and external factors that may influence the obtained estimates.
The reflection of plane waves at the open end of intakes carrying subsonic mean flows are conside... more The reflection of plane waves at the open end of intakes carrying subsonic mean flows are considered in this work. The investigations are conducted with a three-dimensional numerical scheme based on the lattice Boltzmann method. Two different geometry profiles were considered to represent the intake, including a cylindrical bell mouth and a Borda tube. The comparison between numerical and analytical results provided by the low-frequency theory suggested two different traits. For the cylindrical bell mouth, the incoming flow remains potential and the wave reflection is only influenced by the phase velocity shift caused by convection. In such a situation, the available low-frequency theory holds for the entire frequency range of plane wave propagation. Conversely, for sharp geometries, such as the Borda tube, flow separates at the duct's entrance and the wave reflection becomes mostly influenced by the exchange of energy between the flow and the acoustic field. In this case, the numerical results deviate considerably from the theory, even in the low-frequency limit. The mechanisms involving the transfer of rotational kinetic energy from the flow to the acoustic field are discussed and an empirical formula is proposed in terms of reflection coefficient for the entire range of plane wave propagation.
In the context of aircraft noise simulations, an accurate representation of the aircraft noise so... more In the context of aircraft noise simulations, an accurate representation of the aircraft noise sources is crucial so that reliable predictions can be obtained. In this contribution, we present a comparative study between the predictions provided by the emission models based on the DLR's in-house PANAM tool and the sonAIR simulation software. Both are based on semi-empirical descriptions of the engine and airframe noise contributions, meaning that the emission levels are modeled separately for each noise source according to the operational conditions of the aircraft. This allows the comparison of the emission models not only in terms of the aircraft's overall noise levels, but also regarding its different noise sources. The comparative study considers models representing the noise emissions of an A319 aircraft, which are provided by both simulation tools but further simulated within the sonAIR software environment in order to yield noise immission levels on a large calculation area. In general, a good agreement is observed for the departure procedure due to the similar performance of the engine noise models. In contrast, larger differences are observed during the approach procedure and at larger distances from the runway, which might be explained by differences in the airframe noise models.
INTER-NOISE and NOISE-CON Congress and Conference Proceedings
In the context of aircraft noise simulations, an accurate representation of the aircraft noise so... more In the context of aircraft noise simulations, an accurate representation of the aircraft noise sources is crucial so that reliable predictions can be obtained. In this contribution, we present a comparative study between the predictions provided by the emission models based on the DLR in-house code PANAM and the sonAIR simulation software. Both are based on semi-empirical descriptions of the engine and airframe noise contributions, meaning that the emission levels are modeled separately for each noise source according to the operational conditions of the aircraft. This allows the comparison of the emission models not only in terms of the aircraft's overall noise levels, but also regarding its different noise sources. The comparative study considers models representing the noise emissions of an A319 aircraft, which are provided by both simulation tools but further simulated within the sonAIR software environment in order to yield noise immission levels on a large calculation area...
A quantitative approach to density-based clustering of flight trajectories for efficient air traffic noise simulations
INTER-NOISE and NOISE-CON Congress and Conference Proceedings
The continuous growth of air traffic and increased availability of open source data has enabled t... more The continuous growth of air traffic and increased availability of open source data has enabled the application of data-driven approaches for the prediction of noise contours around airports. Aiming at efficient noise simulations, this contribution proposes a framework for the probabilistic description of the air traffic around an airport. The methodology is based on using the density-based clustering algorithm OPTICS to cluster flight trajectories. The clustered trajectories serve as a basis for the creation of backbone and dispersion tracks, which, together with a prescribed number of flight operations per aircraft type, provide a probabilistic description of the air traffic to the noise simulations. A major focus is given to quantitatively assess the sensitivity of the OPTICS algorithm to different hyper-parameters to reduce the dimensionality of the problem. This framework is demonstrated utilizing a dataset of ADS-B trajectory data associated with flights approaching Hannover a...
Computational models of sufficient quality are indispensable to quantitatively assess aircraft no... more Computational models of sufficient quality are indispensable to quantitatively assess aircraft noise reduction measures. Within this study, a multi-level simulation framework is established in order to predict the environmental noise of holding approach procedures by coupling simulation models from three different domains: flight performance calculation employing the base of aircraft data (BADA), jet engine performance using the software Gasturb and aircraft noise simulations based on the software sonAIR. Two different concepts of holding approach procedures are investigated, namely, the vertical holding stack and the linear hold point merge. The study is conducted considering generic air traffic scenarios at a single-runway airport. Thereby, the investigated air traffic is based on a statistical analysis of traffic data at existing airports and thus assumed to be representative. As the aircraft’s noise emission depends on both the aircraft and the engine performance, reliable resul...
In this work, the impact of the COVID-19 outbreak on the environmental noise generated by the air... more In this work, the impact of the COVID-19 outbreak on the environmental noise generated by the air traffic at the Hannover Airport, Germany, is assessed. For this purpose, a comparative study of the air traffic noise in the years 2019 and 2020 is conducted by means of publicly available measurement data and computational simulations. Based on environmental noise directives defined by the responsible German authorities, the comparative study is conducted in terms of A-weighted equivalent sound pressure level metrics computed for the six months of the forecast years with the largest number of flights. In comparison with the year of 2019, the measurement data indicates that the LA,eq,day, LA,eq,night, and Lden were reduced in average by 2.4, 4.2, and 3.7 dBA, respectively, in the year 2020. Furthermore, the results based on the computational simulations show that the isocontour areas of the LA,eq,day=60 dBA and LA,eq,night=55 dBA noise protection zones defined by the German federal gove...
Sound Quality Assessment of a Novel Medium-range Aircraft in the Context of a Sustainable and Energy Efficient Aviation
In the context of the Cluster of Excellence SE2A- Sustainable and Energy-Efficient Aviation, futu... more In the context of the Cluster of Excellence SE2A- Sustainable and Energy-Efficient Aviation, future technologies for a sustainable and eco-friendly air transport system are being investigated. This task requires not only the development of alternative fuel concepts and novel vehicle technologies but also the definition of appropriate assessment strategies. Regarding noise, the assessment should reflect the situation of communities living near airports, i.e. not only addressing noise levels but also accounting for the annoyance caused by aircraft noise. For this purpose, conventional A-weighted sound pressure level metrics provide initial but limited information as the level- and frequency-dependency of the human hearing is accounted for in a simplified manner. Ideally, subjective evaluations are required to adequately evaluate the perceived short-term annoyance associated to aircraft noise. However, this is a rather time-consuming approach to be applied during the conceptual aircraf...
The investigation of technologies that can improve the sustainability of the air transport system... more The investigation of technologies that can improve the sustainability of the air transport system requires not only the development of alternative fuel concepts and novel vehicle technologies but also the definition of appropriate assessment strategies. Regarding noise, the assessment should reflect the situation of communities living near airports, i.e., not only addressing sound levels but also accounting for the annoyance caused by aircraft noise. For this purpose, conventional A-weighted sound pressure level metrics provide initial but limited information as the level- and frequency-dependency of the human hearing is accounted for in a simplified manner. Ideally, subjective evaluations are required to adequately quantify the perceived short-term annoyance associated with aircraft noise. However, listening tests are time-consuming and not suitable to be applied during the conceptual aircraft design stage, where a large solution space needs to be explored. Aiming at bridging this ...
Visualization is an intuitive way to observe and analyse the phenomena related to the propagation... more Visualization is an intuitive way to observe and analyse the phenomena related to the propagation of sound. It is evident that human hearing is highly capable of discriminating different aspects from an acoustic signal. The ability to discriminate is not necessarily enough to identify causality, that is answering the question: what aspect in the audio signal path, being a device or a room, contributes to the perceived difference in sound? Extracting information from a signal and visualizing it is a valuable tool for recognizing causality in cases where direct comparison between conditions via listening is not possible.
The reflection of plane waves at the open end of intakes carrying subsonic mean flows are conside... more The reflection of plane waves at the open end of intakes carrying subsonic mean flows are considered in this work. The investigations are conducted with a three-dimensional numerical scheme based on the lattice Boltzmann method. Two different geometry profiles were considered to represent the intake, including a cylindrical bell mouth and a Borda tube. The comparison between numerical and analytical results provided by the low-frequency theory suggested two different traits. For the cylindrical bell mouth, the incoming flow remains potential and the wave reflection is only influenced by the phase velocity shift caused by convection. In such a situation, the available low-frequency theory holds for the entire frequency range of plane wave propagation. Conversely, for sharp geometries, such as the Borda tube, flow separates at the duct's entrance and the wave reflection becomes mostly influenced by the exchange of energy between the flow and the acoustic field. In this case, the numerical results deviate considerably from the theory, even in the low-frequency limit. The mechanisms involving the transfer of rotational kinetic energy from the flow to the acoustic field are discussed and an empirical formula is proposed in terms of reflection coefficient for the entire range of plane wave propagation.
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Papers by Gil Greco