The Parametric Aircraft Noise Analysis Module - status overview and recent applications

The German Aerospace Center (DLR) is investigating aircraft noise prediction and noise reduction capabilities. The Parametric Aircraft Noise Analysis Module (PANAM) is a fast prediction tool by the DLR Institute of Aerodynamics and Flow Technology to address overall aircraft noise. It was initially developed to (1) enable comparative design studies with respect to overall aircraft ground noise and to (2) indentify promising low-noise technologies at early aircraft design stages. A brief survey of available and established fast noise prediction codes is provided in order to rank and classify PANAM among existing tools. PANAM predicts aircraft noise generated during arbitrary 3D approach and take-off flight procedures. Noise generation of an operating aircraft is determined by its design, the relative observer position, configuration settings, and operating condition along the flight path. Feasible noise analysis requires a detailed simulation of all these dominating effects. Major aircraft noise components are simulated with individual models and interactions are neglected. Each component is simulated with a separate semi-empirical and parametric noise source model. These models capture major physical effects and correlations yet allow for fast and accurate noise prediction. Sound propagation and convection effects are applied to the emitting noise source in order to transfer static emission into aircraft ground noise impact with respect to the actual flight operating conditions. Recent developments and process interfaces are presented and prediction results are compared with experimental data recorded during DLR flyover noise campaigns with an Airbus A319 (2006), a VFW-614 (2009), and a Boeing B737-700 (2010). Overall, dominating airframe and engine noise sources are adequately modeled and overall aircraft ground noise levels can sufficiently be predicted. The paper concludes with a brief overview on current code applications towards selected noise reduction technologies

Auralization of novel aircraft configurations

A joint initiative of NLR, DLR, and TU Delft has been initiated to streamline the process of generating audible impressions of novel aircraft configurations. The integrated approach adds to the value of the individual tools and allows predicting the sound of future aircraft before they actually fly. Hence, an existing process for the aircraft design and system noise prediction at DLR has been upgraded to generate the required input data for an aircraft auralization framework developed by NLR and TU Delft. This paper presents the new process and an initial application towards the fully automated auralization of novel aircraft configurations within the conceptual aircraft design phase. Such an early auralization of the new designs enables the aircraft designer to assess the success of selected low-noise measures in an intuitive way in addition to the conventional measures, e.g. noise isocontour areas. The auralization result is able to capture all the predicted noise shielding measures used in the current application and indicates that, for an approach condition, drastically reduced ground noise exposure can be achieved

Aircraft Noise

This reprint is about aircraft noise. Multidisciplinary topics are covered. One focus is supersonic transport aircraft and their noise generation during approach and take-off. The articles within this study present recent and ongoing research activities from research entities and universities from around the world. This book is beneficial for engineers and researchers that are working the field of aircraft noise

Application of Noise Certification Regulations within Conceptual Aircraft Design

ICAO Annex 16 regulations are used to certify the acoustic performance of subsonic transport aircraft. Each aircraft is classified according to the measured EPNL levels at specific certification locations along the approach and departure. By simulating this certification process, it becomes possible to identify all relevant parameters and assess promising measures to reduce the noise certification levels in compliance with the underlying ICAO regulations, i.e., allowable operating conditions of the aircraft. Furthermore, simulation is the only way to enable an assessment of novel technology and non-existing vehicle concepts, which is the main motivation behind the presented research activities. Consequently, the ICAO Annex 16 regulations are integrated into an existing noise simulation framework at DLR, and the virtual noise certification of novel aircraft concepts is realized at the conceptual design phase. The predicted certification levels can be directly selected as design objectives in order to realize an advantageous ICAO noise category for a new aircraft design, i.e., simultaneously accounting for the design and the resulting flight performance. A detailed assessment and identification of operational limits and allowable flight procedures for each conceptual aircraft design under consideration is enabled. Sensitivity studies can be performed for the relevant input parameters that influence the predicted noise certification levels. Specific noise sources with a dominating impact on the certification noise levels can be identified, and promising additional low-noise measures can be applied within the conceptual design phase. The overall simulation process is applied to existing vehicles in order to assess the validity of the simulation results compared to published data. Thereafter, the process is applied to some DLR low-noise aircraft concepts to evaluate their noise certification levels. These results can then be compared to other standard noise metrics that are typically applied in order to describe aircraft noise, e.g., SEL isocontour areas. It can be demonstrated that certain technologies can significantly reduce the noise impact along most of an approach or departure flight track but have only a limited influence on the noise certification levels and vice versa. Finally, an outlook of the ongoing developments is provided, in order to apply the new simulation process to supersonic aircraft. Newly proposed regulations for such concepts are implemented into the process in order to evaluate these new regulations and enable direct comparison with existing regulations

Flyover noise evaluation of low-noise technologies applied to a blended wing body aircraft

In the frame of the European research project ARTEM (Aircraft noise Reduction Technologies and related Environmental iMpact), new aircraft architectures and alternative propulsion systems, e.g. Blended Wing Body (BWB) and geared turbofan engine concept, are investigated, as well as innovative noise reduction technologies such as metamaterials and low noise high-lift device systems. A noise impact assessment has been performed on a long-haul BWB concept developed by Roma Tre University, using the System Noise Prediction Tools of ONERA (CARMEN) and DLR (PANAM). First, shielding effects on the main noise emission sources are discussed, through installation effects hemispheres at relevant third-octave band frequencies around the aircraft. Based on the shielding assessment, detailed take-off and landing procedures are simulated for several aircraft configurations. Two alternative motorisations of the BWB are evaluated. Finally, the most promising low noise technologies developed in the frame of ARTEM are applied, and their impact on the aircraft’s overall noise levels on the ground is discussed. It can be demonstrated how the specific aircraft configuration, the engine type and the additional low-noise technology result in a significant overall noise reduction. An accompagning conference paper presents flyover auralisations based on these total aircraft noise calculations

Aeroacoustics research in Europe: The CEAS-ASC report on 2022 highlights, Contribution: Uncertainty quantification for aircraft noise emission simulation: methods and limitations

Review paper about the research highlights in the field of aeroacoustics. Assembled by the CEAS ASC, i.e., editors Christophe Schram and Gareth Bennett. The contribution of the authors presents research activities in the field of uncertainty quantification associated with aircraft system noise prediction

Sound quality assessment of a medium-range aircraft with enhanced fan-noise shielding design

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 gap, this work presents a methodology for the sound quality assessment of computational aircraft noise predictions, which is hereby conducted in terms of objective psychoacoustic metrics. The proposed methodology is applied to a novel medium-range vehicle with fan noise shielding architecture during take-off and landing procedures. The relevance of individual sound sources, i.e., airframe and engine noise contributions, and their dependencies on the aircraft architecture and flight procedures are assessed in terms of loudness, sharpness, and tonality. Moreover, the methodology is steered towards community noise assessment, where the impacts on short-term annoyance brought by the novel aircraft design are analysed. The assessment is based on the modified psychoacoustic annoyance, a metric that provides a quantitative description of human annoyance as a combination of different hearing sensations. The present work is understood as an essential step towards low-annoyance aircraft design

Evaluation of flyover auralisations of today's and future long-range aircraft concepts

The European research project ARTEM (Aircraft noise Reduction Technologies and related Environmental iMpact) develops innovative aircraft noise reduction technologies such as advanced engine fan lining, metamaterials and low-noise high-lift systems applied to a vehicle with enhanced shielding of the engine noise, namely, a blended wing body. Using aircraft flyover auralisation in laboratory listening experiments, such future technologies can be evaluated with respect to human sound perception. To assess the reliability of such perception-based evaluations, the simulation should be validated with existing aircraft flyovers. This contribution presents a systematic and rigorous hierarchical validation of auralisations of current jet aircraft using field recordings. Uncertainty in the source modelling is considered by using two different prediction tools for partial sound sources. In addition to comparing computed noise indicators, a psychoacoustic validation is done in laboratory listening experiments with a 3D loudspeaker array. The validation comprises three levels: direct comparison of auralisations with recordings to study the identifiability of auralisations, ranking of auralisations and recordings regarding plausibility, and subjective annoyance ratings to test whether auralisations and recordings differ with respect to noise effects. Further, first results on the comparison of a future concept with a current aircraft are presented

FLIGHT TESTING OF NOISE ABATING RNP PROCEDURES AND STEEP APPROACHES

To test different types of noise abatement approach procedures the Institute of Flight Guidance and the Institute of Aerodynamics and Flow Technology performed flight tests on the 6th September 2010 with a Boeing 737-700. In total 13 approaches to the Research Airport in Brunswick were flown while the approach area of the airport was equipped with six noise measurement microphones. Brunswick airport is equipped with an experimental ground based augmentation system (GBAS) which allows the implementation of 48 ILS lookalike precision approach procedures with different approach angles simultaneously

Simulation of Landing and Take-off Noise for Supersonic Transport Aircraft at a Conceptual Design Fidelity Level

The German Aerospace Center has launched an internal project to assess the noise impact associated with supersonic transport aircraft during approach and departure. A dedicated simulation process is established to cover all relevant disciplines, i.e., aircraft and engine design, engine installation effects, flight simulation, and system noise prediction. The core of the simulation process is comprised of methods at the complexity and fidelity level of conceptual aircraft design, i.e., typical overall aircraft design methods and a semi-empirical approach for the noise modeling. Dedicated interfaces allow to process data from high fidelity simulation that will support or even replace initial low fidelity results in the long run. All of the results shown and discussed in this study are limited to the fidelity level of conceptual design. The application of the simulation process to the NASA 55t Supersonic Technology Concept Aeroplane, i.e., based on non-proprietary data for this vehicle, yields similar noise level predictions when compared to the published NASA results. This is used as an initial feasibility check of the new process and confirms the underlying methods and models. Such an initial verification of the process is understood as an essential step due to the lack of available noise data for supersonic transport aircraft in general. The advantageous effect of engine noise shielding on the resulting system noise is demonstrated based on predicted level time histories and certification noise levels. After this initial verification, the process is applied to evaluate a conceptual supersonic transport design based on a PhD thesis with two engines mounted under the wing, which is referred to as aircraft TWO. Full access to this vehicle’s design and performance data allows to investigate the influence of flight procedures on the resulting noise impact along approach and departure. These noise results are then assembled according to proposed Federal Aviation Agency regulations in their Notice of Proposed Rulemaking, e.g., speed limitations, for Supersonic transport noise certification and the regulations from Noise Chapters of the Annex 16 from the International Civil Aviation Organization in order to evaluate the resulting levels as a function of the flight procedure