Investigation of airframe noise for a large-scale wing model with high-lift devices

The acoustic characteristics of a large-scale model of a wing with high-lift devices in the landing configuration have been studied in the DNW-NWB wind tunnel with an anechoic test section. For the first time in domestic practice, data on airframe noise at high Reynolds numbers (1.1–1.8 × 10⁶) have been obtained, which can be used for assessment of wing noise levels in aircraft certification tests. The scaling factor for recalculating the measurement results to natural conditions has been determined from the condition of collapsing the dimensionless noise spectra obtained at various flow velocities. The beamforming technique has been used to obtain localization of noise sources and provide their ranking with respect to intensity. For flap side-edge noise, which is an important noise component, a noise reduction method has been proposed. The efficiency of this method has been confirmed in DNW-NWB experiments.     

“Buzz-saw” noise: Prediction of the rotor-alone pressure field

Public expectations of lower environmental noise levels, and increasingly stringent legislative limits on aircraft noise, result in noise being a critical technical issue in the development of jet engines. Noise at take-off, when the engines are at high-power operating conditions, is a key reference level for engine noise certification. “Buzz-saw” noise is the dominant fan tone noise from modern high-bypass-ratio turbofan aircraft engines during take-off. Rotor-alone tones are the key component of buzz-saw noise. The rotor-alone pressure field is cut-off at subsonic fan tip speeds; buzz-saw noise is associated with supersonic fan tip speeds, or equivalently, high power engine operating conditions. A recent series of papers has described new work concerning the prediction of buzz-saw noise. The prediction method is based on modelling the nonlinear propagation of one-dimensional sawtooth waveforms. A sawtooth waveform is a simplified representation of the rotor-alone pressure field. Previous validation of the prediction method focussed entirely on reproducing the spectral characteristics of buzz-saw noise; this was dictated at that time by the availability of spectral data only for comparison between measurement and prediction. In this paper, full validation of the method by comparing measurement and prediction of the rotor-alone pressure field is published for the first time. It is shown that results from the modelling based on a one-dimensional sawtooth waveform capture the essential features of the rotor-alone pressure field as it propagates upstream inside a hard-walled inlet duct. This verifies that predictions of the buzz-saw noise spectrum, which are in good agreement with the measured data, are based on a model which reproduces the key physics of the noise generation process. Validation results for the rotor-alone pressure field in an acoustically lined inlet duct are also shown. Comparisons of the measured and predicted rotor-alone pressure field are more difficult to interpret because the acoustic lining significantly modifies the sawtooth waveform, but there remains good agreement with the measured spectral data. The buzz-saw noise prediction code used to generate the simulations in this paper has been used by the Rolls–Royce Noise Department since 2004.     

The effects of environmental and classroom noise on the academic attainments of primary school children

While at school children are exposed to various types of noise including external, environmental noise and noise generated within the classroom. Previous research has shown that noise has detrimental effects upon children's performance at school, including reduced memory, motivation, and reading ability. In England and Wales, children's academic performance is assessed using standardized tests of literacy, mathematics, and science. A study has been conducted to examine the impact, if any, of chronic exposure to external and internal noise on the test results of children aged 7 and 11 in London (UK) primary schools. External noise was found to have a significant negative impact upon performance, the effect being greater for the older children. The analysis suggested that children are particularly affected by the noise of individual external events. Test scores were also affected by internal classroom noise, background levels being significantly related to test results. Negative relationships between performance and noise levels were maintained when the data were corrected for socio-economic factors relating to social deprivation, language, and special educational needs. Linear regression analysis has been used to estimate the maximum levels of external and internal noise which allow the schools surveyed to achieve required standards of literacy and numeracy.     

自适应光学系统的数值模拟：噪音和探测误差的效应

噪音和探测误差是影响自适应光学系统性能的三个主要因素之一。噪音和探测误差使哈特曼－夏克（Hartmann-Shack)波前传感器所测得的华斜量产生误差,进而影响整个自适应光学系统的性能,建立了对噪声和探测误差对哈特曼－夏克波前传感器的影响进行数值模拟的理论模型,编制了计算程序,与已有的激光大气传输与自适应光学系统的计算程序相衔接,进行了模拟计算,对有限的离散采样,读出噪音和光子噪音的效应作了数值模拟研究,获得了一些对于实际的自适应光学系统的最佳设计有价值的结果。     

Noise attenuation in factories

The cost of reducing noise levels in factories by covering large surfaces with sound absorbents is high. It is therefore important to be able to calculate in advance the effectiveness of absorbents and to determine how absorbents may be chosen and distributed for maximal noise reduction for the invested capital. For this purpose a mathematical model of sound propagation and attenuation in factories has been developed on certain simplifying assumptions. The interrelationship between the different parameters is found to be rather intricate and the mathematical model must be evaluated using a computer program. The influence on the noise levels of sound scattering objects, the shape and size of the factory and absorbents on the room surfaces have been studied. Especially if the ceiling is high, acoustic baffles are found to be more efficient than absorbents on the ceiling in reducing noise levels.     

Noise mapping using measured noise and GPS data

In this paper, we introduce a system to easily produce a noise map using noise and GPS data measured simultaneously. The system consists of a sound level meter, a GPS receiver, a database program to manage the measured data, and a program to produce the noise map including a computer model of the target area. The GPS receiver interfaced to the sound level meter allows simultaneous measurement and storage of the noise level and the global position at a location. The database program directly imports one or more measured data stored in the sound level meter. Then, selected measurement results are exported to the noise mapping program for producing colour-coded or noise contour line maps using measured data at user-defined locations. The noise map produced can be exported to DXF and SHP files with other modeling items, for post-processing in GIS software. To demonstrate the capability of the developed system, we show a noise map for a university campus produced by the system.     

Measurement and prediction of speech and noise levels and the Lombard effect in eating establishments

Measurements made of the acoustical characteristics of, and occupied noise levels in, ten eating establishments are described. Levels to which diners and employees were exposed varied from 45 to 82 dB(A). From these levels and diner questionnaire responses, the number of customers present and average noise levels to which individual diners were exposed during their visits were estimated. These data, assumptions about the number of talkers per customer, and classical room-acoustical theory were used to deduce talker voice output levels. These varied from slightly above "casual" to "loud." An iterative model for predicting speech and noise levels in eating establishments, including the Lombard effect as described by a new, proposed model, was developed. With the measured noise levels as the target for prediction, optimization techniques were used to find best estimates of unknown prediction parameters--such as those defining the Lombard effect, the number of talkers per customer, and the average absorption per customer--with highly credible results. The prediction algorithm and optimal parameters constitute a novel model for predicting speech and noise levels--and thus speech intelligibility--in eating establishments, as a function of the number of customers, including a proven, realistic model of the Lombard effect.     

Use of the bertin aérotrain for the investigation of flight effects on aircraft engine exhaust noise

A prototype of the Aérotrain has been modified by SNECMA and Société Bertin to investigate flight effects on jet noise and jet suppressor performance. To this end, special attention was given to the reduction of parasitic noise from the vehicle and internal noise from the GE-J85 turbojet engine which powers the Aérotrain. The vehicle, its performance, the operational techniques, the measurement and analysis procedures used are fully described, together with the results of the calibration tests of this unique and very flexible facility which presents many advantages compared to aircraft in flight. Typical results, consistent with the trends shown by clean aircraft noise data, are presented.     

Spectral estimation method for noisy data using a noise reference

The development of array processing methods to extract the useful characteristics of acoustic sources such as their locations and absolute levels, starting from the measured sound field is one of the main issues in aero-acoustics. The conventional beamforming method is a very popular technique investigated to solve the power level estimation problem. It has the advantage of being robust, easy to implement and cheap in computation time. However, this technique is also known for having poor spatial resolution capabilities which prevents the correct source levels being obtained for numerous practical applications. Deconvolution techniques of the result computed with CBF, with the point spread function of the array manifold, may restore the power levels of the acoustic sources that would be observed in the absence of the array resolution effects. However, the accuracy of the results provided by deconvolution methods is very sensitive to background noise, always present in acoustic measurements. This process should be carried out after the additive noise has been suitably attenuated and, ideally, the deconvolution operator should amplify the noise as little as possible. Another approach is described in the article. It consists in using a noise reference and a new technique called spectral estimation method with additive noise to remove both the smearing effect produced by the array response and the background noise. The technique has been applied to computer and experimental simulations conducted both in an anechoic chamber and in the test section of an open wind tunnel involving acoustic sources radiating in a noisy environment. The levels of the sources were found with a good level of accuracy and the background noise greatly reduced, confirming the validity of the approach and the satisfactory performance of the method proposed.     

Analysis of digital recordings of noise levels using a programmable calculator

The system used at the Building Research Station for analysing digital recordings of noise levels is described. A suite of programs has been developed which analyses the noise recordings and gives values of selected noise units. Time histories of the noise may be plotted using some of the programs.     

Experimental study of noise emitted by circular cylinders with large roughness

The aerodynamic noise generated by high Reynolds number flow around a bluff body with large surface roughness was investigated. This is a relevant problem in many applications, in particular aircraft landing gear noise. A circular cylinder in cross-flow and a zero-pressure-gradient turbulent boundary layer with various types of roughness was tested in a series of wind tunnel experiments. It has been shown that distributed roughness covering a circular cylinder affects the spectra over the entire frequency range. Roughness noise is dominant at high frequencies, and the peak frequency is well described by Howe?s roughness noise model when scaled with the maximum outer velocity. There are differences between hemispherical and cylindrical roughness elements for both the circular cylinder and the zero-pressure-gradient turbulent boundary layer cases, indicating a dependence on roughness shape, not described by the considered roughness noise models. Cylindrical roughness generates higher noise levels at the highest frequencies, especially for the zero-pressure-gradient turbulent boundary layer case. Cable-type roughness aligned with the mean flow does not generate roughness noise, and its spectrum has been found to collapse with the smooth cylinder at medium and high frequencies. At low and medium frequencies the noise spectra have the same features as the smooth cylinder, but with higher shedding peak levels and fall-off levels, despite the decrease in spanwise correlation length. Roughness induces early separation, and thus a shift of the spectra to lower frequencies.     

亚音主旋翼的噪声预测和声隐身分析

本文介绍了基于FW-H方程的亚音主旋翼噪声预测方法,并在螺桨噪声预测程序基础上发展了主旋翼噪声预测程序。本文采用商用CFD软件FINE／TURBO模拟直升机旋翼流场,为噪声预测程序提供所需要的桨叶表面载荷,并用算例验证了载荷数据的准确性和噪声预测程序的有效性。本文计算和讨论了亚音悬停条件下的辐射噪声,并重点分析了不同形状桨叶对辐射噪声的影响,结果表明采用合理的薄翼型叶尖、尖削叶尖及线性扭转桨叶都可以降低辐射噪声,为通过改变桨叶形状降低旋翼辐射噪声提供了合理途径。     

The disturbance caused to school teachers by noise

A survey to investigate the disturbance caused to secondary school teachers by noise is described. Although the survey sample was selected on the basis of road traffic noise exposure it has also been possible to draw conclusions about the disturbance by aircraft noise. Quantitative relationships have been established between the proportions of teachers bothered by noise and the noise level to which they are exposed. The results of this school survey are compared with dwelling noise surveys.     

An exploratory study into the prediction of low frequency traffic noise

An exploratory study whose main aim was to develop equations for the prediction of low frequency traffic noise scales (from traffic parameters) is described. Summaries of noise and traffic measurement procedures are documented and the results of data analysis presented.The equations developed are shown to be accurate, but will require development to cater for more variable site conditions. The equations also indicate the large contribution made to low frequency noise levels by heavy vehicles. The implication of this for ‘lorry nuisance’ is discussed. Broad-band scales are shown to be reasonable surrogates for most, but not all, narrow-band low frequency effects. A method for determining low frequency scales using simple instrumentation is described.This paper is the first of three based on work carried out with the assistance of the Greater London Council (Scientific Branch) and which deal with the prediction of low frequency traffic noise scales and their relevance to vibration disturbance, lorry nuisance and building vibration.     

Calibration of RPC-based muon detector at BESⅢ

The calibration algorithm for RPC-based muon detector at BESⅢ has been developed. The calibration method, calibration error and algorithm performance are studied. The primary results of efficiency and noise at layer, module and strip levels have been calibrated with cosmic ray data. The calibration constants are available for simulation and reconstruction tuning. The results of Monte Carlo and data are also compared to check the validation and reliability of the algorithm.     

Assessment of noise from “quiet” pile drivers

This paper summarizes the results of a study aimed at defining the basic characteristics of noise from a range of pile driving devices which were either adapted or designed specifically to generate noise levels below those normally expected. The parameters studied were noise levels, spectra and waveform shapes. In addition, the noise reduction techniques employed by each manufacturer are described in detail.     

Nature of orchestral noise

Professional orchestral musicians are at risk of exposure to excessive noise when at work. This is an industry-wide problem that threatens not only the hearing of orchestral musicians but also the way orchestras operate. The research described in this paper recorded noise levels within a professional orchestra over three years in order to provide greater insight to the orchestral noise environment; to guide future research into orchestral noise management and hearing conservation strategies; and to provide a basis for the future education of musicians and their managers. Every rehearsal, performance, and recording from May 2004 to May 2007 was monitored, with the woodwind, brass, and percussion sections monitored in greatest detail. The study recorded dBALEQ and dBC peak data, which are presented in graphical form with accompanying summarized data tables. The findings indicate that the principal trumpet, first and third horns, and principal trombone are at greatest risk of exposure to excessive sustained noise levels and that the percussion and timpani are at greatest risk of exposure to excessive peak noise levels. However, the findings also strongly support the notion that the true nature of orchestral noise is a great deal more complex than this simple statement would imply.     

Noise exposure of workers of the construction sector

Noise is one of the most highly found physical contaminants in the construction sector. The most negative effects caused by noise exposure are related to the hearing system and may produce professional deafness or even permanent deafness. As these effects have a very important influence on people’s health and well-being, it is necessary to assess the noise exposure and to develop mechanisms for studying and proposing preventive solutions.This work has studied the noise levels which the workers of the construction sector are exposed to. A number of representative measurements have been carried out using a sound level meter and a dosimeter to collect data from workers devoted to different tasks in the construction process. Analysis of the most important levels and indexes have been done with those data, and afterwards, they have been compared with the limits imposed by the different current regulations.