Showing papers on "Aircraft noise published in 2018"

Improving the soundscape quality of urban areas exposed to aircraft noise by adding moving water and vegetation

Abstract: Research shows that the sight of trees and the sound of moving water improve the soundscape quality of outdoor spaces exposed to road traffic noise. Effects are attributed to non-energetic masking, visual attentional distortion, and congruence between sight and hearing. However, there is no literature on such effects for aircraft noise. Aircraft noise varies from other traffic sources, i.e., in terms temporal variability, duration, and spectral composition, complicating the application of findings without further research. In a virtual reality experiment reported in this article, participants were asked to rate scenarios with different sound levels of flyovers, urban typologies, vegetation, and/ or water features. The results showed a significant improvement of the soundscape quality when (1) vegetation and (2) moving water were present, and especially when (3) vegetation and moving water were presented simultaneously, especially for residential areas in terms of the relative change. Moving water also reduced the saliency of aircraft flyovers significantly, changing the constellation of fore- and background sounds. Moving water raised the perceived audibility of the most dominant sound source too, which could be attributed to non-energetic masking effects. The findings of this study indicate that soundscape strategies can complement noise abatement in areas prone to aircraft noise.

Aircraft Noise and Psychological Ill-Health: The Results of a Cross-Sectional Study in France.

Abstract: Background: The effects of aircraft noise on psychological ill-health have not been largely investigated and remain to be discussed. No study has been performed in France on the health effects of aircraft noise. Objectives: The present study aimed to investigate the relationship between aircraft noise in dB and in terms of annoyance and psychological ill-health in populations living near airports in France. Methods: A total of 1244 individuals older than 18 and living near three French airports (Paris–Charles de Gaulle, Lyon–Saint-Exupery and Toulouse–Blagnac) were randomly selected to participate in the study. Information about their personal medical history and socioeconomic and lifestyle factors was collected by means of a face-to-face questionnaire performed at their place of residence by an interviewer. Psychological ill-health was evaluated with the 12-item version of the General Heath Questionnaire (GHQ-12). For each participant, outdoor aircraft noise exposure in dB was estimated by linking their home address to noise maps. Objective noise exposure in dB was considered to be the primary exposure of interest. Four noise indicators referring to three different periods of the day were derived and used for the statistical analyses: Lden, LAeq,24hr, LAeq,6hr–22hr, and Lnight. Noise annoyance and noise sensitivity were the secondary risk factors of interest. Logistic regression models were used with adjustment for potential confounders. Results: The participation rate in the study was 30%. Approximately 22% of the participants were considered to have psychological ill-health according to the GHQ-12. No direct association was found between exposure to aircraft noise in dB and psychological ill-health. However, annoyance due to aircraft noise and noise sensitivity were both significantly associated with psychological ill-health. Moreover, a gradient was evidenced between annoyance and psychological ill-health, with increasing ORs from 1.79 (95% CI 1.06–3.03) for people who were not all annoyed to 4.00 (95% CI 1.67–9.55) for extremely annoyed people.Conclusions: These findings confirm the results of previous studies, suggesting there is no direct association between aircraft noise exposure in dB and psychological ill-health, but there is a significant relationship between noise sensitivity or annoyance due to aircraft noise and psychological ill-health. This supports the hypothesis that psychological aspects, such as noise annoyance and noise sensitivity, play important roles in the association between environmental noise and adverse effects on health. However, further studies are necessary in order to better understand the links between these variables.

Tonal Noise Prediction of a Distributed Propulsion Unmanned Aerial Vehicle

Abstract: Noise is expected to be a major barrier of unmanned aerial vehicles (UAVs) to public acceptance. A noise prediction scheme is introduced in this paper and applied to a specific vehicle configuration, namely, the Greased Lightning-10. Results herein will be used to demonstrate the feasibility of incorporating a noise constraint within the flight control system of a distributed electric propulsion vehicle by modifying commands for low-noise operation over sensitive areas, e.g., communities, schools, etc. Steady loading and thickness noise signatures of single propellers are computed using the Propeller Analysis System of the NASA Aircraft NOise Prediction Program. The individual signatures are then superposed at far field observers after applying corrections for spherical spreading and phase delays based on straight ray propagation. Two-propeller source fields are verified using analytical directivity patterns of monopoles. Notional effects of rotation rate, rotation direction, and relative propeller phase are given. Under ideal circumstances and equivalent RPM, random phasing, which occurs in most small UAVs, can produce up to 20 decibels uncertainty in the tonal sound pressure level at a given ground observer. Additionally, directivity modification via relative propeller phase control is shown to have great potential as a noise reduction technique. This paper will focus on the forward flight mode but will also briefly discuss the vertical flight mode.

Microphone arrays for imaging of aerospace noise sources

Abstract: With the continuous growth in demand for air traffic and wind turbines, the noise emissions they generate are becoming an increasingly important issue. To reduce their noise levels, it is essential to obtain accurate information about all the sound sources present. Phased microphone arrays and acoustic imaging methods allow for the estimation of the location and strength of sound sources. Experiments with these devices are one of the main approaches in the current research in aeroacoustics, along with computational simulations or noise prediction models. This thesis presents a detailed literature review on the most common aerospace noise sources, challenges in aeroacoustic measurements, and the acoustic imaging methods typically used to overcome them. Practical recommendations are provided for selecting the appropriate imaging technique depending on the type of experiment. New integration techniques for distributed sound sources, such as leading– or trailing–edge noise, are proposed in this thesis and are proven to provide the best performance in retrieving the source levels, compared to other well–known methods. In addition, the high–resolution version of the deconvolution method CLEAN–SC, HR–CLEAN–SC, is explained and applied to wind–tunnel measurements. It is confirmed that this method can resolve sound sources at half the frequency associated with the Rayleigh resolution limit, while keeping the inherent advantages of CLEAN–SC. The most appropriate acoustic imaging methods (according to the recommendations from the literature study) were applied to aeroacoustic experiments and compared with other approaches, when possible. Since the landing gear is considered as the dominant airframe noise source in commercial aircraft, this source was analyzed using four different approaches: aircraft flyover measurements under operational conditions, full–scale wind–tunnel experiments, computational simulations and noise prediction models. Strong tonal noise at certain frequencies was observed and suggested the presence of open cavities. Noise prediction models do not account for this behavior and seem to provide erroneous estimates. Eliminating the contribution of the cavity will reduce the noise levels considerably. Trailing–edge noise is considered to be the dominant noise source for modern wind turbines. The performance of the two most promising noise reduction measures was investigated in wind–tunnel experiments. First, trailing–edge serrations featuring different geometries were studied and showed noise reductions of more than 10 dB. In case a serration–flow misalignment angle occurs, the performance of the serrations decreases and they even cause a noise increase after a crossover frequency. Similar results were found with computational simulations. Secondly, trailing–edge porous inserts showed noise reductions of approximately 10 dB at low frequencies and a noise increase after a crossover frequency. It is argued that the reasons for these phenomena were, respectively, the cross–flow between the pressure and suction sides of the airfoil and the increased roughness of the porous material with respect to the solid case. Lastly, the issue of the variability in aircraft noise levels was considered, since it is not properly taken into account by current best practice noise prediction models and hinders the enforcement of environmental laws. It was observed that variations in the fan rotational speed explain a large part of this variability. Two different approaches were proposed for estimating the fan rotational speed of aircraft flyovers based on audio recordings. Implementing these more accurate estimates of this parameter in the noise prediction model (rather than the default values as usual) considerably reduces the errors made and provide more accurate aircraft noise estimates. In conclusion, phased microphone arrays have confirmed their importance for aeroacoustic studies, such as measuring aircraft noise emissions under operational conditions and assessing the performance of noise reduction measures.

Aircraft noise and self-assessed mental health around a regional urban airport : a population based record linkage study

Abstract: Limited evidence suggests that residential exposure to aircraft noise negatively influences population mental health around large airports, but it is not known whether the same is true for smaller airports. We investigated whether residential exposure to aircraft noise near a regional urban airport was associated with risk of chronic self-assessed mental ill health. This is a cross-sectional study of 198,532 people aged 18 years and over living in Belfast, United Kingdom, enumerated at the 2011 Census. Residential exposure to aircraft noise (LAeq,16h) was assessed by linking Census records with modelled noise contours surrounding George Best Belfast City Airport (c.42,000 annual aircraft movements). Associations between noise and mental ill health were estimated using multiple logistic regression adjusting for demographic characteristics, socio-economic status and comorbidity. Prevalence of self-assessed mental ill health was greater in high noise (≥57 dB) compared to low noise (< 54 dB) areas (12.4% vs. 9.7%). We found no association between aircraft noise and risk of mental ill health after adjustment for socio-economic status (high vs. low noise odds ratio: 1.03 CI: 0.93, 1.14). Associations between aircraft noise and mental health have been reported near large airports at similar average noise levels to those observed here. Our findings indicate that the noise environment around this smaller airport (with fewer flights and no night flights) has little influence on population mental health.

Assessing aircraft noise-induced annoyance around a major German airport and its predictors via telephone survey – The COSMA study

Abstract: Background Despite technological improvements and noise mitigation schemes, annoyance due to aircraft noise remains an ongoing issue for residents near airports, and increasing annoyance has been observed in many affected communities. Objectives This study investigates aircraft noise-induced annoyance near a German airport that is particularly busy at night. In addition to established predictors, it examines variables not considered in studies of recent years. Annoyance ratings are compared to the current European standard exposure-response curve and the community tolerance level (Lct) is calculated as described in the 2016 revision of ISO 1996-1. Methods A telephone survey was conducted with 1262 residents near Cologne/Bonn Airport (IATA: CGN, Germany) which can be classified as a low-rate change (LRC) airport. Acoustical (Ldn in 5 dB-steps, flight altitude , and predominant type of operation) and non-acoustical variables (e.g., attitudes, noise sensitivity, urbanisation level of area) were recorded for every participant. Respondents assessed their aircraft noise-induced overall annoyance as well as their night-time annoyance using the verbal 5-point ICBEN scale. Results The Ldn explained 16.5% of variance in the annoyance ratings. The inclusion of non-acoustical variables into the regression model increased the proportion of explained variance to 54.8%. Annoyance prevalence rates at CGN were higher than predicted by the EU-standard curve and the Lct was lower than predicted by recent work. Conclusion For a LRC airport, the community around CGN shows an uncommonly high percentage of highly annoyed residents and a low tolerance to aircraft noise exposure. Non-acoustical factors including personal and situational factors seem to have substantial impact on annoyance.

Air traffic assignment to reduce population noise exposure using activity-based approach

Abstract: Aircraft noise has been regarded as one of the major environmental issues related to air transport. Many airports have introduced a variety of measures to reduce its impact. Several air traffic assignment strategies have been proposed in order to allocate noise more wisely. Even though each decision regarding the assignment of aircraft to routes should consider population exposure to noise, none of the air traffic assignment strategies has addressed daily migrations of population and number of people exposed to noise. The aim of this research is to develop a mathematical model and a heuristic algorithm that could assign aircraft to departure and arrival routes so that number of people exposed to noise is as low as possible, taking into account temporal and spatial variations in population in an airport’s vicinity. The approach was demonstrated on Belgrade airport to show the benefits of the proposed model. Numerical example showed that population exposure to noise could be reduced significantly by applying the proposed air traffic assignment model. As a consequence of the proposed air traffic assignment, overall fuel consumption increased by less than 1%.

Aircraft Noise Assessment—From Single Components to Large Scenarios

Abstract: The strategic European paper “Flightpath 2050” claims dramatic reductions of noise for aviation transport scenarios in 2050: “...The perceived noise emission of flying aircraft is reduced by 65%. These are relative to the capabilities of typical new aircraft in 2000...”. There is a consensus among experts that these far reaching objectives cannot be accomplished by application of noise reduction technologies at the level of aircraft components only. Comparably drastic claims simultaneously expressed in Flightpath 2050 for carbon dioxide and NOX reduction underline the need for step changes in aircraft technologies and aircraft configurations. New aircraft concepts with entirely different propulsion concepts will emerge, including unconventional power supplies from renewable energy sources, ranging from electric over hybrid to synthetic fuels. Given this foreseen revolution in aircraft technology the question arises, how the noise impact of these new aircraft may be assessed. Within the present contribution, a multi-level, multi-fidelity approach is proposed which enables aircraft noise assessment. It is composed by coupling noise prediction methods at three different levels of detail. On the first level, high fidelity methods for predicting the aeroacoustic behavior of aircraft components (and installations) are required since in the early stages of the development of innovative noise reduction technology test data is not available. The results are transferred to the second level, where radiation patterns of entire conventional and future aircraft concepts are assembled and noise emissions for single aircraft are computed. In the third level, large scale scenarios with many aircraft are considered to accurately predict the noise exposure for receivers on the ground. It is shown that reasonable predictions of the ground noise exposure level may be obtained. Furthermore, even though simplifications and omissions are introduced, it is shown that the method is capable of transferring all relevant physical aspects through the levels.

A Systematic Review of the Basis for WHO’s New Recommendation for Limiting Aircraft Noise Annoyance

Abstract: The new WHO Environmental Noise Guidelines for the European Region have recommendations for limiting noise exposure associated with adverse health effects. The limits are said to be based on a systematic review of existing evidence. This paper gives a systematic assessment of the presented evidence with respect to annoyance from aircraft noise. The new guidelines have been based on the results from a selection of existing aircraft noise studies. This paper demonstrates that a similar selection of other existing post-2000 studies will yield very different results. In addition, the validity of the presented evidence has been questioned as some of the referenced studies have not been conducted according to standardized methods, and the selection of respondents is not representative of the general airport population.

Modeling of Aircraft Takeoff Weight Using Gaussian Processes

Abstract: The takeoff weight of an aircraft is an important aspect of aircraft performance. However, the takeoff weight of a particular flight is generally not available to entities outside of the operating ...

The Development of a Multiple-Item Annoyance Scale (MIAS) for Transportation Noise Annoyance

Abstract: In 2001, Team#6 of the International Commission on Biological Effects of Noise (ICBEN) recommended the use of two single international standardised questions and response scales. This recommendation has been widely accepted in the scientific community. Nevertheless, annoyance can be regarded as a multidimensional construct comprising the three elements: (1) experience of an often repeated noise-related disturbance and the behavioural response to cope with it, (2) an emotional/attitudinal response to the sound and its disturbing impact, and (3) the perceived control or coping capacity with regard to the noise situation. The psychometric properties of items reflecting these three elements have been explored for aircraft noise annoyance. Analyses were conducted using data of the NORAH-Study (Noise-Related Annoyance, Cognition, and Health), and a multi-item noise annoyance scale (MIAS) has been developed and tested post hoc by using a stepwise process (exploratory and confirmatory factor analyses). Preliminary results were presented to the 12th ICBEN Congress in 2017. In this study, the validation of MIAS is done for aircraft noise and extended to railway and road traffic noise. The results largely confirm the concept of MIAS as a second-order construct of annoyance for all of the investigated transportation noise sources; however, improvements can be made, in particular with regard to items addressing the perceived coping capacity.

Selection of an Audibility Criterion for Propeller Driven Unmanned Aerial Vehicle

Abstract: Based on a flight experiment, the difference between the total aircraft noise level and the ambient noise is proposed to be used as an audibility criterion for unmanned aerial vehicles equipped with piston engines. It is found that the unmanned aerial vehicle becomes audible for an observer at a criterion value of 3 dBA.

Two-dimensional Modal Beamforming in Wavenumber Space for Duct Acoustics

Abstract: As turbofan bypass ratio continues to increase, civilian aircraft noise is increasingly dominated by fan noise. Fan noise propagating from its rotor and stator origins to the community passes through the inlet or aft flow duct, where its confined situation makes it susceptible to characterization by wall-mounted microphone arrays. Recently, the NASA-Glenn Research Center adapted its W-8 Single Stage Axial Compressor Facility to this type of measurement. OptiNav, Inc. took the opportunity to improve and simplify the duct mode processing in its Beamform Interactive computer program. A new approach to in-duct beamforming with a 2D wall-mounted array of microphones was developed. The purpose of this paper is to document the beamforming approach and provide some sample results from the W-8 facility.

Assessing the shielding of engine noise by the wings for current aircraft using model predictions and measurements.

Abstract: Reducing aircraft noise is a major issue to be dealt with by the aerospace industry. In addition to lowering noise emissions from the engine and airframe, also the shielding of engine noise by the aircraft is considered as a promising means for reducing the perceived noise on the ground. In literature, noise shielding predictions indicate significant reductions in received noise levels for blended wing body configurations, but also for conventional aircraft with the engines placed above the wings. Little work has been done in assessing these potential shielding effects for full aircraft under real operational conditions. Therefore, in this work, noise shielding for current aircraft is investigated using both measurements and model predictions. The predictions are based on the Kirchhoff integral theory and the Modified Theory of Physical Optics. For the comparison between the predictions and measurements, Twenty Fokker 70 flyovers are considered. The data analysis approach for the extraction of shielding l...

Electric Motor Noise from Small Quadcopters: Part 1 - Acoustic Measurements

Abstract: There is increased interest in using electric motors to drive propulsors across a range of small air vehicle classes. Applications include both vertical lift and conventional takeoff and landing systems for Small Unmanned Aircraft Systems. Mission profiles call for integrating these systems into urban airspaces exposing populated areas to new noise sources. In addition to the propulsor noise from rotors and propellers, electric motors are expected to contribute to the overall sound levels and possibly human annoyance. This work presents acoustic measurements of electric motors used for small quadcopters to characterize the sound and identify sources with and without a propeller. Free field microphone measurements were used to determine directivity and a phased microphone array was used to identify sound sources. A companion paper (Part II - Source Characteristics and Prediction) compares the far field results with current probe measurements of the signal driving the motor, the structural response of the motor case, and describes prediction methods of electric motor noise.

Aircraft System Noise Assessment of the NASA D8 Subsonic Transport Concept

Abstract: Avehicle-level noise assessment has been performed for theNASAD8 concept aircraft (ND8) in the NASA Advanced Air Transport Technology Project portfolio. The NASA research-level Aircraft NOise Prediction Program (ANOPP-Research) was used to predict the noise from each source component on the ND8 to build up a noise estimate for the full aircraft. The propulsion airframe aeroacoustic (PAA) effects of the ND8, namely boundary layer ingestion (BLI) with its influence on fan noise, and the noise shielding, reflection, and diffraction mechanisms of the unconventional airframe, were empirically modeled using experimental data. Noise reduction technologies appropriate to the 2025-2035 time frame were included in this study. Including all technologies and PAA effects, the ND8 is predicted to have a cumulative margin to the Stage 4 certification metric of only 7.4 EPNdB. Boundary layer ingestion is predicted to have a detrimental impact on cumulative noise levels on the order of 15 EPNdB. Fan noise is seen to be the primary noise source at all three certification points, even if the BLI noise impact could be entirely suppressed. The impact of engine noise shielding by the airframe is limited by a lack of aft shielding and the presence of horizontal tail reflections in the aft direction. The physical constraint on engine size by the pi-tail is seen as a potential barrier to engine noise reduction through the corresponding limitation on fan bypass ratio. Mildly reduced climb performance (compared to similar reference aircraft) does not provide any benefit through increased noise propagation distance. If the boundary layer ingestion noise penalty could be suppressed such that BLI would have no effect on noise, the cumulative margin to Stage 4 would increase to 22.4 EPNdB, still below the NASA Mid Term goal of 32-42 EPNdB.

Dependence of High-performance Military Aircraft Noise on Frequency and Engine Power

Abstract: To further understand the unique characteristics of military aircraft noise, the sound field in the vicinity of a tied-down F-35B was measured for various engine powers, from 25% to 150% Engine Thrust Request (ETR). Synchronous measurements along a linear ground array approximately parallel to the shear layer were used to image the entire field through multisource statistically optimized near-field acoustical holography (M-SONAH). The field in the direction of maximum radiation consists of multiple lobes in the spatiospectral domain, which are manifest as multiple local maxima in space for a fixed frequency or multiple peaks in the spectra at a fixed location. Multiple lobes are observed at non-afterburning and afterburning engine conditions. As frequency increases for a given engine power, lobes appear towards the sideline and shift aft until they disappear beyond the measurement aperture and new lobe(s) take their place. As engine power is increased at a fixed frequency, the forwardmost lobe increases in its relative contribution to the field, which is a major contributing factor to the forward shift in overall directivity with increasing engine power. Field reconstructions and data in the forward direction outside of the region of maximum radiation show the presence of broadband shock-associated noise (BBSAN) for 75% ETR and above. Reconstructions along the nozzle lipline of the jet indicate the BBSAN originates from approximately the same region as the sources for the main radiation direction

Aeroacoustics of isolated and installed jets under static and in-flight conditions

Abstract: In modern aircraft configurations, the interaction between the exhausted jet with the wing and high-lift devices is set to increase substantially the total aircraft noise generated during take-off. Regarding ultra-high bypass ratio turbofan engines mounted underneath the wing, the jet plume is expected to interact strongly with rigid surfaces. The interaction between the high-speed flow and aircraft structures modifies the ‘pure’ jet mixing noise and enhance the scattered hydrodynamic field. Thus, understanding the changes to the jet turbulence flow field caused by the presence of a solid boundary is vital to predict and mitigate the engine noise produced by commercial aircraft which will be introduced imminently. In this thesis, the statistics of the streamwise component of the velocity of subsonic jets is investigated in detail. In close-coupled installed jet configurations, the interaction between the jet and a rigid surface leads to a local flow acceleration and to lower turbulence levels near the solid boundary. These effects are consistent with the conservation of momentum and the ‘beak-down’ of the eddies in that region. The characteristic length scales of these installed jet configurations are smaller than the isolated jet scales. The effects of forward flight upon the turbulence field is also considered. A stretching factor with flight velocity is obtained by considering the jet virtual origin. Models for the coherence decay, time and length scales are proposed based on experimental evidence and the assumption of frozen turbulence in the region of maximum turbulence kinetic energy. For the first time, two-point statistic models are proposed for high-subsonic and installed jet configurations. Finally, analysis of the far field of installed jets show that a strong interaction between the jet turbulence field and a solid boundary generates an additional high-frequency noise. Thus, the existence of a noise source mechanism related to the flow-structure interplay is demonstrated. It is hoped that the experimental data and analysis presented in this work provide feedback for jet noise source modelling and also future numerical and large-scale laboratory experiments.

10 Years of Joint Research at DLR and TU Braunschweig toward Low-Noise Aircraft Design - What Did we Achieve? (invited keynote presentation)

Abstract: This invited keynote lecture reviews the last years of joint research activities between DLR and TU Braunschweig in the field of low-noise aircraft design. This joint research has been initiated around 2008 between the DLR Institute of Aerodynamics and Flow Technology and the Institute of Aircraft Design and Lightweight Structures at TU Braunschweig. In that time, DLR has developed a first version of an aircraft noise prediction tool called the Parametric Aircraft Noise Analysis Module (PANAM). This tool has been implemented as a module into the aircraft design synthesis code Preliminary Aircraft Design and Optimization (PrADO) by TU Braunschweig. For the first time, a fully automated and fully parametric aircraft design process with integrated noise prediction capabilities was established. The main focus lies on conventional tube-and-wing aircraft with turbofan and turboprop engine concepts. Ever since, both tools have been under constant development and the simulation chain for low-noise aircraft design has been applied to various aircraft concepts. The presentation reviews the tool development, the most important applications, highlights some lessons learnt, and is complemented with an outlook on future developments and applications.

Problem of the Community Noise Reduction for Aircraft with Open Rotor Engines

Abstract: This paper considers the problem of community noise for an aircraft with contra-rotating open rotors. Main noise sources are described. Basic methods of noise reduction are considered. A noise reduction method by increasing the axial spacing between propellers is proposed from the test results.

Far Term Noise Reduction Roadmap for the Mid-Fuselage Nacelle Subsonic Transport

Abstract: A noise reduction technology roadmap study is presented to determine the feasibility for the Mid-Fuselage Nacelle (MFN) aircraft concept to achieve the noise goal set by NASA for the Far Term time frame, beyond 2035. The study starts with updating the noise prediction of the existing MFN configuration that had been modeled for the time frame between 2025 and 2035. The updated prediction for the Mid Term time frame is 34.3 dB cumulative effective perceived noise level (EPNL) below the Stage 4 regulation. A suite of technologies that are deemed feasible to mature for practical implementation in the Far Term and whose potentials for noise reduction have been illustrated is selected for analysis. For each technology, component noise reduction is modeled either by available experimental data or by physics-based modeling with aircraft system level methods. The noise reduction is then applied to the corresponding noise component predicted by advanced aircraft system noise prediction tools, and the total aircraft noise is predicted as the incoherent summation of the components. It is shown that the Far Term MFN aircraft has the potential to achieve a cumulative noise level of 40.2 EPNL dB below Stage 4. The key technologies to achieve this low aircraft noise level are assessed by the impact of each technology on the aircraft system noise. This roadmap shows the potential of this revolutionary, yet still tube-and-wing, MFN concept to reach the NASA Far Term noise goal.

Experimental validation of the hybrid scattering model of installed jet noise

Abstract: © 2018 Author(s). Jet installation causes jet noise to be amplified significantly at low frequencies, and its physical mechanism must be understood to develop effective aircraft noise reduction strategies. A hybrid semi-empirical prediction model has recently been developed based on the instability-wave-scattering mechanism. However, its validity and accuracy remain to be tested. To do so, in this paper we carry out a systematic installed jet-noise experiment in the laboratory using a flat plate instead of an aircraft wing. We show that reducing H (the separation distance between the flat plate and jet centerline) causes stronger low-frequency noise enhancement while resulting in little change to the noise shielding and enhancement at high frequencies. Decreasing L (the axial distance between the jet exit plane and the trailing edge of the plate) results in reduced noise amplification at low frequencies and also weakens both the shielding and enhancement at high frequencies. Increasing the jet Mach number abates the installation effects. It is shown that the hybrid model developed in the earlier work agrees with experimental measurements and can capture the effects of varying H, L, and jet Mach number extremely well. It is concluded that the model captures the correct physics and can serve as an accurate and robust prediction tool. This new physical understanding provides insights into innovative strategies for suppressing installed jet noise.

NASA's Pursuit of Low-Noise Propulsion for Low-Boom Commercial Supersonic Vehicles

Abstract: Since 2006, when the Fundamental Aeronautics Program was instituted within NASA's Aeronautics Mission Directorate, there has been a Project looking at the technical barriers to commercial supersonic flight. Among the barriers is the noise produced by aircraft during landing and takeoff. Over the years that followed, research was carried out at NASA aeronautics research centers, often in collaboration with academia and industry, addressing the problem. In 2013, a high-level milestone was established, described as a Technical Challenge, with the objective of demonstrating the feasibility of a low-boom supersonic airliner that could meet current airport noise regulations. The Technical Challenge was formally called "Low Noise Propulsion for Low Boom Aircraft", and was completed in late 2016. This paper reports the technical findings from this Technical Challenge, reaching back almost 10 years to review the technologies and tools that were developed along the way. It also discusses the final aircraft configuration and propulsion systems required for a supersonic civilian aircraft to meet noise regulations using the technologies available today. Finally, the paper documents the model-scale tests that validated the acoustic performance of the study aircraft.

Technical and economical factors in green roof using to reduce the aircraft noise

Abstract: The relevance of research is due increased environmental tensions associated with the noise impact of transport, including the problem of aircraft noise. The purpose of the study is the development of reduce the impact of aircraft noise on the population living near airports, and assessment of the cost-effectiveness of measures to implement measures to reduce noise interference with the device of green roof systems on residential and public buildings near aviation facilities. The predominance of green spaces, architectural forms and other elements of improvement contribute to improving the environment, quality of life, including by reducing the noise load. Based economic analysis and assessment of the noise situation use greening strucrures that improve the well-being of the local population, this particularity concerns the provision of health and psychological comfort of the population. The assessment of the ecological and economic efficiency of green roof systems has shown that the benefits of the green spaces are multifunctional, and in addition to reducing noise, they also reduced the island's effect of heat by creating a shadow, reduce the need for conditioning, reduce wind load, filter harmful emissions, improve air quality and preserve biodiversity.

Structural equation models of road traffic and aircraft noise annoyance in Vietnam

Abstract: Socio-acoustic surveys on the community response to transportation noise were carried out in five Vietnamese cities from 2005 to 2013. Approximately 9900 responses were obtained from these surveys. Variations in exposureâ–“response curves were found among different regions and noise sources. Various degrees of annoyance resulting from the same noise exposure implied the effects of non-acoustic factors, such as urban lifestyles and attitudes towards noise sources. To assess these effects, structural equation models were developed in this study by linking questionnaire items from the socio-acoustic surveys on road traffic and aircraft noise annoyance. The sample sizes were 3783 and 1973 for road traffic and aircraft noise surveys, respectively; therefore, they were sufficiently large to estimate and compare the models among cities and between two types of noise source. The final model included three latent factors: sensitivity, activity interference, and satisfaction with the living environment. Sensitivity to noise, vibration, and heat were determinants of personal sensitivity. Activity interference was measured by awakening during sleep, rest, and listening disturbances. The quietness of living areas, preference for living areas, and comfort during the dry season were used to determine satisfaction with the living environment. A good model fit was observed, indicating that sensitivity and satisfaction with the living environment were the main modifiers of noise annoyance in Vietnam. The findings of this study suggest measures for reducing noise annoyance among urban residents in Vietnam.