8,073 research outputs found
Propeller noise
No full textPropellers consist of a number of rotating blades and produce both tonal (or harmonic) and broadband noise. However, the former is by far the dominant source as it affects community noise, certification noise, and cabin noise. Hence, considerable effort has been expended advancing efficient methods of calculating it. Isolated propellers produce tones at multiples of the blade passing frequency, whereas counter-rotating propellers (CRPs) produce tones at frequencies corresponding to “sum and difference” frequencies of the blade passing frequencies of the front and rear rotors. In most instances, quadrupole noise can be neglected, and analytic expressions can be derived for predicting the noise from the remaining sources, which is due to the thickness of, and the loading on, the propeller blades. While the principles are well understood, good predictions depend on an accurate modeling of the flow fields.<br/
Counter-rotation propeller tip vortex interaction noise
No full textCounter-rotation propeller tip vortex interaction noise occurs when tip vortices, shedfrom each of the upstream propeller blades, interact with the blades on the downstreampropeller. This paper describes two separate models for calculating the noise produced bythis interaction. The first model approximates each tip vortex as a helical vortex tube ofinfinite extent while the second is based on a previously published study and uses a twodimensionalapproximation to model the tip vortex interaction and represents the velocityfield induced by the tip vortices as a piecewise function for which the flow incident on thedownstream blade row must be calculated numerically. The unsteady loading on thedownstream propeller blades is determined from the incident flow predicted using either ofthe models and is used to calculate the radiated sound field using an analytic propeller noiseformul
Representative-in-class vehicles for fleet-level aviation noise analysis
No full textGlobal air traffic demand is projected to nearly double by 2035 (7.2 billion passengers) compared to the 3.8 billion passengers in 2016. At such a growth rate, the aviation sector might cause an important detriment of the welfare of those living around airports via a substantial increase in noise. For addressing such a concern, the aviation industry is required to assess a significant number of aviation scenarios, involving different technology platforms and operational procedures, in order to define the strategies that ensure the higher reduction in aircraft noise impact. A common approach to reduce the combinatorial nature of fleet-level studies and enable more flexibility for exploring multiple aviation scenarios, is to simplify the fleet into a number of representative-in-class vehicles that capture the noise performance of the various classes within the fleet. In this paper, a statistical classification process is implemented for reducing the UK commercial fleet into a number of representative-in-class vehicles based on aircraft noise characteristics. The optimal number of representative-in-class aircraft is analysed for three airports in the UK (London Gatwick, Heathrow and Stansted), with significant differences in aircraft movements and fleet composition, on the basis of the accuracy vs. computational time when calculating noise contour areas. Finally, it is discussed the use of these representative-in-class vehicles as baseline models for projecting the reduction in aviation noise impact with future technology implementation.</p
On the CO2 and noise emissions forecast in future aviation scenarios in the UK
No full textAircraft operations have a significant impact on local air quality, climate change, fuel consumption and noise around airports. In order to reach emission targets set by aviation agencies (e.g. ACARE), to reduce environmental impact and to ensure a sustainable future of the sector, the aviation industry is continuously investing in research and development of technologies for reducing CO2, noise and other emissions. However, different technology platforms might have different effects in terms of CO2 and noise emissions reduction, e.g. Counter-Rotating Open-Rotors (CROR) are estimated to achieve higher reduction in fuel consumption but lower noise reduction than future turbofan designs. On the basis of fuel-burn and noise reduction trend projections found in the relevant literature, this work is aimed at addressing a comparative analysis between the reduction in noise and CO2 emissions of imminent and future generations that will replace current aircraft. Based on the concept of airport noise efficiency, and for easily performing CO2 versus noise interdependencies analyses, a metric for assessing aircraft noise efficiency is defined. Moreover, CO2 and noise emissions are forecast for a number of future aviation scenarios in the UK, on the basis of different aviation growth rates and aircraft technologies
Measurements of the single-point and joint turbulence statistics of high subsonic jets using hot-wire anemometry
No full textThis paper describes a systematic and comprehensive hot-wire investigation into the turbulent statistics of low-, moderate- and high-speed subsonic jets. Experiments were performed to obtain the one-point and two-point statistics of a single-stream, unheated jet turbulence field over a broad region of the jet plume. Results show that hot-wires can be used to measure both the one-point and two-point statistics of the high turbulence intensity, noise-producing regions of unheated, compressible, subsonic jets. For the two-point measurements, probe pairings are performed over the three orthogonal axes. Analysis of the experimental data reveals four main conclusions: (1) both the statistical and joint moments of the turbulence scale well with the local jet shear layer half-width; (2) a simple relationship exists between the statistics of the velocity fluctuations and the square of the velocity fluctuations; (3) a simple relationship exists between the longitudinal and transverse length-scales, and (4) a semi-empirical model has been developed to predict the cross-correlation coefficients, power spectral density, frequency-dependent length-scales and coherence decay of the turbulent velocity field. From the second and third conclusions, it is shown that, in the locations near an eddy’s centre of rotation (i.e. the midpoint of the jet shear layer), the turbulence statistics can be described as quasi-homogeneous and quasi-frozen. The joint statistical moments, therefore, can be inferred simply from single-point tests. These results will help to develop models for predicting jet mixing noise, highlighting the situations in which the simplifying assumptions are inadequate. Graphical abstract: [Figure not available: see fulltext.].</p
A model for the rapid assessment of the impact of aviation noise near airports
No full textThis paper introduces a simplified model (Rapid Aviation Noise Evaluator – RANE) for the calculation of aviation noise within the context of multi-disciplinary strategic environmental assessment where input data is both limited and constrained by compatibility requirements against other disciplines. RANE relies upon the concept of noise cylinders around defined flight-tracks with the Noise Radius determined from publicly available Noise-Power-Distance curves rather than the computationally intensive multiple point-to-point grid calculation with subsequent ISOcontour interpolation methods adopted in the FAA’s Integrated Noise Model (INM) and similar models. Preliminary results indicate that for simple single runway scenarios, changes in airport noise contour areas can be estimated with minimal uncertainty compared against grid-point calculation methods such as INM. In situations where such outputs are all that is required for preliminary strategic environmental assessment, there are considerable benefits in reduced input data and computation requirements. Further development of the noise-cylinder-based model (such as the incorporation of lateral attenuation, engine-installation-effects or horizontal track dispersion via the assumption of more complex noise surfaces formed around the flight-track) will allow for more complex assessment to be carried out. RANE is intended to be incorporated into technology evaluators for the noise impact assessment of novel aircraft concepts
Interaction between a flat plate and a circular subsonic jet
No full textThis paper reports an extensive near- and far-field analysis of the noise generated by an isothermal, subsonic, circular jet in the presence of a solid, flat plate shield. Far-field polar and azimuthal acoustic images are presented initially to characterize the interaction noise source. Near-field streamwise microphone phase analysis along the plate trailing edge reveals a deeper understanding of the link between the jet hydrodynamic field (both linear and non-linear regions) and the mechanisms behind interaction noise generation. Near-field point spectrum data have also been used successfully to validate Amiet's far-field trailing edge dipole prediction code for low-speed jet acoustic Mach numbers.</p
Subjective dominance as a basis for selecting frequency weightings
No full textThe objective of this paper is to propose and illustrate a simple approach for the selection of frequencyweightings for the assessment of environmental and transportation noise. In recent years,the A-frequency weighting has become almost universal except where existing standards and regulationsmandate the use of alternative weightings and/or frequency summation procedures, but evenwhere this has been based on extensive research, no real consensus has been achieved. The proposedapproach is based on the concept of subjective dominance, which does not always conformto the physically dominant frequencies identified by the A- or other frequency weightings and summationprocedures used in measurements and/or predictions. The proposed approach is illustratedby the results of a limited series of five listening tests that clearly demonstrate that no single objectivefrequency weighting or summation procedure is capable of providing the best-fit to subjectiveresponses across a range of different contexts. Subjective dominance varies across different listeningcontexts and situations, and should, therefore, be considered whenever noise management andcontrol decisions are being made. The proposed approach will naturally require further researchbecause of the wide range of different contexts and situations in which it might need to be applied
A new method for estimating community noise changes due to aircraft technology variations
No full textFuture air traffic growth forecasts underline the need for new environmental abatement strategies for aviation, involving, among others, the adoption of new aircraft designs and technologies. Accurately predicting the noise impact of these strategies is therefore a matter of significance. The reliability of existing tools is governed by tradeoffs between parameters such as their fidelity level, their dependence on confidential data, as well as the cost and accuracy of experimental data. This paper proposes an innovative, flexible and simplified method for aircraft noise prediction that by-passes the difficulties of existing models. Based on scenarios where community noise levels are known through existing tools or publicly available databases, the proposed method determines variations resulting from aircraft technology changes, such as the increase of the bypass ratio of a turbofan engine. The method shows promise of being applicable to new designs like the wing body aircraft, whereas, by adapting the input variables, it can also estimate the noise impact of changes at operational level. To illustrate the proposed method, which is part of a wider effort to better understand environmental and economic interdependencies, noise estimations are compared to existing NPD data
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