Abhishek K. Sahai

Incorporating and Minimizing Aircraft Noise Annoyance during Conceptual Aircraft Design

The assessment of aircraft noise for community noise impact and certification has till now been performed conventionally using the A-weighted decibel (dBA) and Effective Perceived Noise Level (EPNL) metrics respectively. Although these metrics have sufficed till now for conventional noise assessment, the renewed interest in unconventional engines such as Counter Rotating Open-Rotor (CROR) engines and the much stronger tonal content their spectra contain may require new unconventional metrics, which fully capture the individual characteristics and complexities of aircraft noise. The focus of this paper shall be on the annoyance aspect of aircraft noise rather than solely on intensity and how this annoyance could be incorporated and minimized during conceptual aircraft design. The research builds on the previous research into aircraft noise annoyance at RWTH Aachen where the sound quality metrics of loudness and tonality were compared to the more conventional metrics dBA, PNL, PNLT and EPNL for standard and noise abatement aircraft procedures. The same approach shall now be applied to aircraft and engine design parameters. It will be seen what influence various design parameters such as number of fan blades and stator vanes, fan tip design Mach number, primary and secondary jet areas, wing span and wing area among others, have on the annoyance caused by aircraft noise via the sound quality metrics of loudness, tonality and sharpness. This will be done using the ILR Noise Simulation and Assessment module INSTANT. A comparison will be made for the currently used conventional metrics, to see if the sound quality metrics capture more information than dBA and EPNdB both for community as well as certification noise assessment. Also, an attempt shall be made for minimal aircraft noise annoyance optimization during conceptual design, via a reduced tonality variant of selected aircraft, using the conceptual aircraft design and optimization environment MICADO of the ILR. The research in this paper is intended as a follow-up to the work carried out for the interdisciplinary internal RWTH Aachen project – Virtual Air Traffic System Simulation (VATSS) which had the aim of making aircraft noise more easily communicable via auralization and 3D visualization of air-traffic.

Interdisciplinary Auralization of Take-off and Landing Procedures for Subjective Assessment in Virtual Reality Environments

The issue of aircraft noise experienced by residents in the airport’s neighborhoods is one of subjective annoyance and a presentation of noise intensity in decibels alone might not be sufficient to give a clear understanding of noise abatement measures being carried out or the effect for instance of constructing a new runway at an airport. Although noise contours can be a great way of a quick assessment of noise impact over larger areas, noise quantified in numbers can prove lacking in capturing the actual annoyance caused by the noise to the residents. For this reason, a method providing a more subjective assessment of aircraft noise impact is required and auralization of complete aircraft movements could be one such way of better capturing the annoyance due to noise caused by aircraft. The Virtual Air Traffic System Simulation (VATSS) interdisciplinary project of RWTH Aachen University has the aim of presenting the effect of complete aircraft movements via visualization and auralization of aircraft noise in 3-D Virtual Reality environments for the subjective assessment of aircraft noise. This paper focusses on the interdisciplinary collaboration of the Institute of Aerospace Systems and the Institute of Technical Acoustics of RWTH Aachen to produce a capability of auralizing complete time-dependent take-off and landing procedures up to an altitude of 3000 meters. The noise produced by a conventional aircraft with a turbofan engine is modeled and the ILR’s capability to model aircraft noise for complete 4-D take-off and landing procedures is shown along with the technique to auralize complete standard procedures as well as noise abatement procedures with time-varying settings. Both broadband and tonal noise components for dominant sources are auralized for the movements.

Aircraft Design Optimization for Lowering Community Noise Exposure Based on Annoyance Metrics

This paper focuses on the annoyance aspect of aircraft noise, which relates to the quality of the sound reaching communities, and attempts to potentially lower this annoyance by optimizing an aircr...

Quantifying the audible differences in measured and auralized aircraft sounds

This paper aims to present a way with which audible differences in measured and auralized (i.e. aurally simulated) aircraft noise can be quantified. The purpose of the study is to find a means with which the subjective differences between measured and synthesized sounds can be expressed in an objective manner. The quantification would firstly enable developers of auralization technology to identify more concretely in which aspects the differences exist, in order to make the auralizations sound more realistic. The quantification would secondly aid in developing a means of distinguishing between aircraft sounds in general, beyond the conventional metrics of A-weighted level (dBA) or Effective Perceived Noise Level (EPNL). Such a capability can allow target functions to be developed with which aircraft can be optimized for specific, more acceptable sounds. As used widely in other industries such as the automotive sector, use of sound quality metrics is made to quantify the differences in the quality of the sounds. The comparison is carried out in terms of both conventional and sound quality metrics for the audio of a reference aircraft, which has been measured and auralized over the same flight paths at a noise monitoring station in the airport vicinity.

Potential changes in aircraft noise sound quality due to continuous descent approaches

This paper presents an analysis of how flying Continuous Descent Approaches (CDAs) can affect the quality of sounds that aircraft produce in airport vicinities. It is well known that CDAs present potential benefits in terms of community noise impact with reductions in excess of 5 dBA in peak noise levels. It is however unclear if these reductions in A-weighted level, which is a poor predictor of perceived annoyance, also correspond to an improvement in the quality of the aircraft sounds that reach the residents on the ground. A real comparison can only be made by comparing the sounds an aircraft produces while flying a CDA with a standard approach procedure. A short-range and a long-range aircraft are simulated to fly a standard approach procedure and a CDA with 3, 4, and 5 degree glideslope angle. The noise produced over both approach procedures is then auralized at representative ground locations, and the sounds are analyzed for changes in sound quality. Quantifying the changes in the aircraft sounds in...

Methodology for designing aircraft having optimal sound signatures

This paper presents a methodology with which aircraft designs can be modified such that they produce optimal sound signatures on the ground. With optimal sound it is implied in this case sounds that are perceived as less annoying by residents living near airport vicinities. A novel design and assessment chain has been developed which combines the aircraft design process with an auralization and sound quality assessment capability. It is demonstrated how different commercial aircraft can be designed, their sounds auralized at representative locations in airport vicinities and subsequently assessed for sound quality. As sound quality is closely related to the perceived annoyance, it is expected that designs with improved sound quality would also be perceived as less annoying. By providing a feedback to the design optimizer in terms of one of the sound quality metrics or a suitable combination thereof, the designs of aircraft can be altered to produce potentially less annoying sounds. The paper will focus on three current aircraft and will demonstrate the application of the novel design chain to auralize and alter their sounds toward improved sound quality. The presented methodology can also be extended to unconventional aircraft configurations and propulsion concepts, for optimizing future aircraft sounds.