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Abstract The structure of exhaust system influences the loudness of exhaust noise significantly. This paper indicates the impact of the structure parameters of exhaust system on the loudness of exhaust tail noise and presents an evaluation model to conduct the improvement of exhaust system for improved loudness. Firstly, the twenty-seven structure samples are designed by orthogonal experiment and exhaust tail noises of those are obtained by simulation. The accuracy of simulation is also validated by the experiment successfully. Then the structure-loudness model is developed by the radial basis function (RBF) network technique. Subsequently, the contributions and main effects of the structure parameters on loudness are indicated in this work. Finally, based on the structure-loudness model, the robust optimum design for improved loudness is studied by the adaptive simulated annealing (ASA) algorithm. The result of optimization certifies that the structure-loudness model is useful for the optimization. The method applied in this paper can be feasible for other psychoacoustic metrics. [ABSTRACT FROM AUTHOR]

Abstract There are well-established measurement standards for the rating of impact noise reduction provided by floor coverings in relation to structurally transmitted impact noise, e.g. BS EN ISO 10140-3 and ASTM E492 are widely used in Europe and North America Respectively. Standardisation for "in-room" impact noise transmitted by an airborne path is however less well established. At the current time the standard used for rating the "in-room" impact sound reduction is BS EN 16205:2013 which focuses primarily on walking noise as a the impact source. This standard employs the same tapping machine used for impact improvement testing in BS EN ISO 10140-3 but has been found not to be ideal due to the mechanical noise it produces and because it is not fully representative of the walking loads that the standard primarily aims to address. There is currently no standard that deals with "in room" impact noise from falling objects which may be a greater concern than walking noise, for example in a healthcare or education setting. Thus, presented in the paper are the findings from a large measurement survey conducted to investigate the influence of impactor mass, hardness and velocity on measured "in room" impact noise reductions. Other measurands such as the reduction in impact force and floor acceleration are also considered. It is discussed in the paper how 'In-room' impact noise differs from transmitted impact noise and this is demonstrated by performing a transfer path analysis to separate out the impact noise contributions from a falling object and from the floor. The key finding of the study is that the whilst the impact noise reduction achieved by different floor coverings varies wildly for different impactor types the rank order of the floor coverings tested in terms of Impact noise reduction did not. Thus, the ideal test method may not be the one that simulates best the type of impacts a floor is likely to be subjected to, but rather, it ought to be the one that gives the biggest differences between similar floor coverings so as to highlight most clearly the differences between them. [ABSTRACT FROM AUTHOR]

Centrifugal fans have several technical applications. Their aerodynamic performance is well-optimized nowadays, but the same does not apply to their acoustic performance. Noise control studies of centrifugal fans are often focused on designed operating conditions or operating conditions close to the onset of instability. This paper seeks to find an alternative geometry of the centrifugal fan impeller which would improve noise control of centrifugal fans in a wide range of operating conditions. In this paper, the term noise control refers to noise level reduction and additionally to manipulating the psychoacoustic properties of noise. The experimental work and numerical calculations focus on the centrifugal fan in vacuum cleaners. The experimental work, based on numerical simulations, is described to investigate the influence of the triangular cross section on the flow channel, formed by two inclined blades in opposite directions, on aerodynamic properties and the psychoacoustic performance of the impeller. The study demonstrates that impellers with a triangular flow channel achieve an aerodynamic performance which is comparable to that of standard impellers. The results also show that impellers with inclined blades deliver superior results in psychoacoustic metrics compared to impellers with upright blades. [ABSTRACT FROM AUTHOR]

• The CNOSSOS-EU method is not presently accurate for the assessment of railway noise, perhaps due to the contention that CNOSSOS-EU input values are limited and of variable quality [1]. • Acoustic modelling using the previously applied interim calculation method RMR-1996 compared to the new CNOSSOS-EU methodology produced estimates suggesting that 91,692 more persons may experience exposure to railway noise > 55 dB(A) L den . • Reviews should be conducted in respective EU nations, and a nationally applicable rail vehicle XML catalogue should be created to best represent national fleets in their entirety, and as recommended by the EU in the END. Since December 2018 a harmonised approach for the assessment of transportation noise, known as CNOSSOS-EU, became obligatory for EU Member States in the calculation of strategic noise mapping. This paper provides an assessment of rail-based environmental noise in Ireland via a comparative analysis of acoustic modelling for rail sources in the Irish context by comparing the CNOSSOS-EU method and the previously utilised interim method RMR-1996 with field measurements. The paper also presents comparative estimates of population exposure calculated using CNOSSOS-EU and RMR-1996. It was found that the results generated by the CNOSSOS-EU model were closer to field measurements when compared to the RMR-1996 model. Noise modelling also indicated that populations estimated to be exposed to levels of railway noise > 55 dB(A) generated by the national rail fleet were higher using CNOSSOS-EU (i.e. 91,692 more persons) relative to the RMR-1996 method. Rail noise generated by the Luas tram rail network generated marginally less population exposure for railway noise > 55 dB(A) (i.e. 2,905 less persons) relative to RMR-1996. As such, the paper contributes to the assessment of the new CNOSSOS-EU model for rail in the EU and addresses the relative lack of research focusing on rail modelling and population exposure estimation under the END. This paper contributes to a better understanding of the extent that populations are exposed to railway noise using CNOSSOS-EU across Europe. [ABSTRACT FROM AUTHOR]

The urban sound environment of New York City (NYC) can be, amongst other things: loud, intrusive, exciting and dynamic. As indicated by the large majority of noise complaints registered with the NYC 311 information/complaints line, the urban sound environment has a profound effect on the quality of life of the city’s inhabitants. To monitor and ultimately understand these sonic environments, a process of long-term acoustic measurement and analysis is required. The traditional method of environmental acoustic monitoring utilizes short term measurement periods using expensive equipment, setup and operated by experienced and costly personnel. In this paper a different approach is proposed to this application which implements a smart, low-cost, static, acoustic sensing device based around consumer hardware. These devices can be deployed in numerous and varied urban locations for long periods of time, allowing for the collection of longitudinal urban acoustic data. The varied environmental conditions of urban settings make for a challenge in gathering calibrated sound pressure level data for prospective stakeholders. This paper details the sensors’ design, development and potential future applications, with a focus on the calibration of the devices’ Microelectromechanical systems (MEMS) microphone in order to generate reliable decibel levels at the type/class 2 level. [ABSTRACT FROM AUTHOR]

The band-limited linear predictive coding (BLPC) vocoder-based adaptive feedback cancellation (AFC) removes the high-frequency bias, while the low frequency bias persists between the desired input signal and the loudspeaker signal in the estimate of the feedback path. In this paper, we present a BLPC vocoder-based adaptive feedback canceller with probe noise with an objective of reducing the low-frequency bias in digital hearing-aids. A step-wise mathematical analysis of the proposed feedback canceller is presented employing the recursive least square and normalized least mean square adaptive algorithms. It is observed that the optimal solution of the feedback path is unbiased for an unshaped probe noise, but is biased for a shaped probe signal; the bias term does not consist of correlation between the desired input and the loudspeaker output. The identifiability conditions are analysed and it is shown that a delay, greater than or equal to the length of the adaptive filter, must be introduced in the forward path to achieve an unbiased feedback path estimate. Algorithm analysis and computer simulations presented in this paper justify the reason for selecting the proposed design over the existing BLPC vocoder-based feedback cancellation algorithm. [ABSTRACT FROM AUTHOR]

It has been 20 years since the European Commission adopted the Green Paper on Future Noise Policy in 1996, taking the first comprehensive step towards the development of an EU-wide noise policy. This document envisioned a directive that would harmonise methods for the assessment of environmental noise and the dissemination of information to the public. This led to the establishment of Directive 2002/49/EC in 2002 also known as the Environmental Noise Directive (END). The END called for the development of strategic noise maps and action plans across every EU Member State in five year intervals. Two phases of noise mapping and action planning have now been completed and Member States are about to embark on the third phase of noise mapping, due in 2017. Focussing on results reported to the European Commission, this study summarises the current state of noise mapping, 20 years after the publication of the Green Paper, and identifies critical needs for future noise mapping phases. [ABSTRACT FROM AUTHOR]

Tire acoustic cavity resonance (TACR) noise is one of the significant sources causing vehicle interior noise at low-frequency band. Since the rotating and loading conditions can split TACR frequencies, TACR noise exhibits a relatively narrow frequency band, which becomes a challenge to attenuate this type of noise. To deal with this problem, the reduction method of the Helmholtz resonator (HR) group installed inside a lightweight aluminum alloy wheel is adopted in this paper. By the combination welding of spoke and rim in aluminum alloy wheel of a passenger vehicle, the internal annular hollow area is generated as the installation space for this HR group. Great advantages of this manufacturing process are the lightweight and easy installation performances for the wheel. According to the theoretical analyses based on the superposition of traveling waves and its experimental validations, the frequency bands of TACR noise for a rotating tire are determined. To reduce the noise, HR group consisting of 5 different sizes is designed by the Finite Element Method (FEM). Meanwhile, the sound-reducing tire-wheel assembly incorporated with the designed HR group is manufactured and tested by the bench and vehicle experiments. A remarkable reduction can be observed at the peak and specified frequency range of TACR noise. Moreover, the performance also proves to be stable and robust under various road and speed conditions. This paper provides a comprehensive and feasible process strategy for the development of noise-reducing wheel. [ABSTRACT FROM AUTHOR]

An increase in public awareness of noise pollution and the impact of noise on human health has led to the need for enhanced insight in complex noise situations. This insight is commonly obtained either by brief measurements or by evaluation of a simplified acoustic model. Both of these approaches however have limitations in complex noise situations. Noise monitoring can be an appropriate and cost efficient measure to obtain more insight, for it allows to measure at many locations for long periods of time. Monitoring can for example be used to improve the accuracy of models or to assess and respond to changes in the acoustic situation. Several monitoring approaches, for various applications, have been developed or are under development. In the first part of this paper an overview is given of current developments in acoustic monitoring networks and their key aspects. Sensor networks for environmental noise monitoring are here divided into four different categories, distinguished by five aspects: hardware costs, scalability, flexibility, reliability and accuracy. These five aspects determine the range of applications for which a network is suited. In the second part of this paper a monitoring network developed in-house is used to further illustrate the relevance of these aspects. This network was designed to facilitate research into the field of acoustic monitoring networks and is used to experiment with and learn from a broad field of applications. Since the network is not designed for just one application, it has a special focus on flexibility and scalability. This allows the network to cope with the requirement of various applications with different scales. In the third section of this paper three applications of the network are shown to illustrate the five aspects. [ABSTRACT FROM AUTHOR]

The paper analyzes and compares spectral properties of an acoustic noise produced by mechanical vibration of the gradient coils during scanning in the open-air magnetic resonance imager (MRI) working in a weak magnetic field. Selection of a usable type of the vibration sensor and the noise pickup microphone for measurement in weak magnetic field conditions is also discussed. The changes in acoustic noise spectral properties caused by loading of the holder of the lower gradient coils by the weight of the examined person lying in the scanning area of the MRI device is analyzed, too. The achieved results will be first of all used to design a correction filter for noise suppression in the speech signal recorded simultaneously with 3D human vocal tract scanning. Finally, the paper describes measurement and determination of the time delay between the resulting noise signal and the vibration impulses originated in the gradient coils. The obtained results will serve for description of the influence of the vibration on the acoustic noise and the way it travels through the plastic holder in the MRI device scanning area. [ABSTRACT FROM AUTHOR]

This paper proposes a method of measuring the powertrain noise, which enables for the indoor prediction of the sound pressure level (SPL) of pass-by noise in an early stage of vehicle development phase. The proposed method is implemented in two steps. Firstly, the indoor tyre/roller noise is obtained by the indoor coast-by experiment based on the proposed single coast-by approach. Secondly, the powertrain noise is computed by subtracting the tyre/roller noise from the total vehicle noise. Then the powertrain noise is synthesized with the outdoor tyre/road noise energetically to predict the level of pass-by noise, with the purpose of reducing the influence caused by the difference between indoor and outdoor tyre/road noise. The proposed method is validated by experimental comparisons with the existing methods, shielding method and slick-tyre experiment method, respectively. The results show that the proposed method not only produces better prediction accuracy than the existing ones, but also has the ability to predict the pass-by noise SPL for a realistic case in an evaluation time of less than one hour. [ABSTRACT FROM AUTHOR]

Recent years have seen a growing interest in the potential for the use of sonic crystals as noise barriers. The frequencies of highest attenuation can be found by assuming that an integer number of half wavelengths fits the distance between the scatterers. However, this leads to a reduction in its usefulness as a viable noise barrier technology, due to the necessary increase in overall crystal size to increase frequency range of noise reduction. Additional attenuation bands may be achieved if the array is composed of resonant elements instead of solid cylinders. The paper presents resonant sonic crystal barrier that could be applied to stationary but movable noise sources eg. power generator. The results of simulation results were confronted with the results of previous work in this field. This work presents also sound insulation measurements conducted over sonic crystal noise barrier according to the European standard EN 1793-6. In most of the reference literature, sound insulation and reflection properties of sonic crystals are measured or a diffuse sound field or in a direct sound field including the top and side edge diffraction effects together with the transmitted (or reflected) components. The aim of this work is to perform free-field measurements over a real-sized sample in order to verify the points of strength and weakness of the application of standardised measurements to sonic crystals. [ABSTRACT FROM AUTHOR]

Tyre cavity resonance can significantly affect vehicle interior noise at frequencies around 200 Hz. The insertion of a sound absorbing liner inside the tyre is known to be an efficient countermeasure, in fact nowadays tyre manufacturers are already producing tyres implementing this kind of solution. The present work, through analytical and numerical models, supported by material testing, provides a methodology for predicting the dag performance of a lined tyre, taking into account tyre/lining geometry and sound absorbing material properties. The results reported in the paper show that for fixed material characteristics, the attenuation of the cavity resonance is mostly influenced by the volume of the lining treatment. Moreover, the numerical model developed for discontinuous treatments, suggests that for fixed volume and material properties, the cavity resonance attenuation can be increased by choosing a proper layout. [ABSTRACT FROM AUTHOR]

This paper provides a new Acoustic Design Sensitivity (ADS) method for the minimization of noise on landing gear parts. The idea consists of direct differentiation of the closed-forms expressions of the acoustic pressure levels with respect to the landing gear design parameters. The outlines of the method are presented herein by considering semi-empirical formulations proposed for the acoustic pressure level but can be straightforwardly applied to other acoustics weak integral formulations or analogies. Indeed, the estimates of the noise level derivatives allow assessment of the most acoustically sensitive design parameters. Numerical implementation of the ADS method has been performed using SCILAB open code and validated by comparing with the derivatives calculated using Finite Difference Methods (FDM). Then, the sensitivity estimates have been used to minimize different (SPL and OASPL) noise objectives for a generic landing gear. The numerical examples clearly demonstrated the ability of the (ADS) method to accurately identify the appropriate design parameters that will control the bulk of the noise sensitivity. In addition, the optimum solution of the noise minimization problems is exclusively dependent on these design parameters. [ABSTRACT FROM AUTHOR]

Exposure to excessively high noise levels is a relevant health problem in Europe and road traffic noise is the most widespread noise source. When considering cold climate countries, the available scientific literature on noise emission properties of winter tyres is still very limited. In order to contribute into filling this knowledge gap, this paper investigates the acoustical performance of different types of tyres, with focus on winter tyres, on different road surfaces, at different speeds, and with different states of wear. The results indicate that studded winter tyres have, indeed, an increased noise level at frequencies between 315 Hz and 10 kHz, having a significantly different response especially at frequencies higher than 4 kHz. The acoustical response also depends on the tyre type when comparing different road surfaces, as a result of conflicting vibrational and aerodynamic noise generation mechanisms. Additionally, the relationship between labelled and measured values was explored, however, no statistically significant relationship was found between them (and labelling is not applied for studded tyres). A frequency spectrum correction was attempted based on previous measurements on an ISO track, which reduced the difference between measured and labelled values, however, further investigation is still required to properly understand differences between label and road measurements, where the label is determined on a test track with a special, smooth surface. [ABSTRACT FROM AUTHOR]

• Identification of the interactional noise source in the gap between two side-by-side placed propellers. • Noise source imaging on a realistic hovering drone inside a large anechoic chamber using a 8 × 9 microphone array on the ground. Noise source features of multi-propeller systems are experimentally studied in this paper. Noise sources on a pair of side-by-side placed small-scale propellers and a flying quad-copter are investigated separately using microphone arrays and the conventional beamforming algorithm. A high-intensity noise source spot is identified within the gap area between two propeller disks, which is a result of the interaction between the blade tip and upwash flow within the gap area. As the two propellers move away from each other, the noise source spot becomes weaker. Similarly, for a quad-copter under realistic flight conditions, the strongest noise sources are observed within the gap between each of two adjacent propellers, showing the feasibility and repeatability of the result obtained in the lab. The results discussed in this paper show that for the low-noise design of a multi-propeller drone, not only is the single propeller noise, but also the propeller interactional noise shall be taken into account. [ABSTRACT FROM AUTHOR]

Abstract: Noise in a laser printer is affected by many components, such as spring force, spring constant, and friction coefficient. Objective evaluation of pick up noise is difficult because of background noises, such as operating sound. In particular, pick up noise generated between the friction pad and paper in the process of printing has become an essential aspect of quality evaluation. However, the existing criteria for evaluating pick-up noise have solely relied on subjective human judgments; therefore, there is a need to objectify these criteria. In this paper, the noise index for determining the existence of pick-up noise is established using a modified tonality at just noticeable sound level limit. The study has investigated factors that cause pick-up noise and suggests the substitution of printer components that determine spring constants, spring force, and the quality of friction pads. The proposed noise index is successfully applied to classifying the pick-up noise and mitigating the noise through the optimized design combination of laser printer components. [Copyright &y& Elsevier]

The paper presents the development of parameter-based criteria for application of the highly impulsive noise adjustment, which can be the extension to the approach described in standard ISO 1996-1:2016. All calculations in paper are based on the highly impulsive noise example - collision of the train cars. The research material was a record of data collected during two months of continuous noise monitoring, followed by statistical analysis of the subject. The classification based on the analysis of exposure levels was compared with the objective method proposed by the authors, based on the analysis of the distinctive characteristics of impulsive noise: impulsiveness of a given event and its rise time. As a result, three types of impulsive events: clear, masked and weak impulses were proposed with recommendation of criteria when to apply the impulsive adjustment in relation to time of a day. [ABSTRACT FROM AUTHOR]

Abstract: The rolling noise from tyre–pavement interaction represents the greatest sound contribution from a vehicle when cruising at a high speed. To evaluate the sound levels from this source, existing standardized methods that establish different measurement procedures in both the immediate tyre surroundings, for example the Close-Proximity method, as well as at greater distances, as the Coast-By method. A fundamental parameter that can quantify the sound generation of a source is its sound power level. The standardized methods establish procedures to measure the sound pressure level but not the power level of a tyre as a noise source. For this reason, this paper presents a novel methodology based on sound pressure measurements to obtain the sound power level that a vehicle emits in Coast-By conditions, where noise is generated at tyre/road interaction. The paper describes the testing procedure used to obtain the sound power level, and it is accompanied by a mathematical simulation that studies the feasibility of the proposal. Finally, the proposed methodology is further validated through a field study. [Copyright &y& Elsevier]

Abstract: In many industrial and military situations it is not practical or economical to reduce ambient noise to levels that present neither a hazard to hearing nor annoyance. In these situations, personal hearing protection devices are capable of reducing the noise by 20–30dB. Although the use of a hearing protector is recommended as a temporary solution until action is taken to control the noise, in practice, it ends up as a permanent solution in most cases. Therefore, hearing protectors must be both efficient in terms of noise attenuation and comfortable to wear. Comfort in this case is related to the agreement of the user to wear the hearing protector consistently and correctly at all times. The purpose of this paper is, firstly, to provide some background on the publications related to earmuff comfort, most of which are based on measurement of the total headband force and subjective evaluation using questionnaires. Most of the published results show a weak correlation between total headband force and subjective evaluation. Secondly, this paper presents a new method to measure the contact pressure distribution between the earmuff cushions and the circumaural flesh of the human head and estimate a comfort index. The comfort parameters were investigated and equations developed to calculate comfort indices and overall quality indices. The most important calculated comfort index is measured from the contact pressure distribution and correlated with a subjective evaluation. Measurement results for the pressure distribution of 10 earmuffs show good correlation with the subjective evaluation. [Copyright &y& Elsevier]

Graphical abstract Highlights • We consider two-channel convolutive mixture systems. • We present new two-channel sub-band forward decorrelation algorithm (SFD). • We propose a modification of this SFD algorithm based on normalized step-sizes. • The convergence speed and the steady-state values characteristics are improved. • SegMSE and CD criteria show the good performances of second proposed algorithm. Abstract The two-channel forward adaptive filtering algorithms show a good performance in terms of speech-noise separation. The symmetric adaptive decorrelation (SAD) algorithm represents an efficient solution to resolve the acoustic noise reduction problem. The drawback of the classical full-band forward SAD algorithm is its poor performance in term of convergence rate (low) and speech quality (less). In this paper, we propose two contributions. (i) Firstly, a new sub-band configuration of forward decorrelation algorithm (SFD) is proposed to improve the convergence rate. (ii) Secondly, we propose an extended version of the first proposed SFD algorithm based on normalized step-sizes (SNFD). To validate the good performances of two proposed SFD and SNFD algorithms, intensive experiments are done. The obtained results show good performances of these algorithms in comparison with the basic full-band version. [ABSTRACT FROM AUTHOR]

Highlights • The helical-cable technique is to reduce cylinder noise and tandem cylinder noise. • The method can suppress the vortex shedding process and noise radiation efficiency. • Control on the upstream cylinder is the key for the tandem cylinder noise reduction. Abstract Cylinder noise can be remarkably reduced when the surface is helically wrapped with cables along the cylinder span. In this paper, aeroacoustic and aerodynamic experiments are conducted to reveal the noise reduction mechanism of the helical-cable technique. With the application of helical cables on the single circular cylinder, three-dimensional flow is promoted into the cylinder near wake, leading to the suppression of two-dimensional vortex shedding process and flow fluctuations. Besides, the three-dimensional wake also destroys the in-phase relationship of flow fluctuations along the cylinder span, leading to the reduction of spanwise correlation length and noise radiation efficiency. These two effects together contribute to the cylinder noise reduction. Furthermore, this helical-cable technique is extended to tandem cylinders and the results show that it can also reduce the tandem cylinder noise effectively. Especially for the moderate and large spacing tandem cylinder configurations, the key of the noise reduction is the control on the upstream cylinder. [ABSTRACT FROM AUTHOR]

Abstract Tyre/road sound emissions have been proved to be the main source of noise caused by road traffic when traveling at medium and high speeds (Sandberg and Ejsmont, 2002). Tyre/road noise has been widely studied among the last decades. However, an important part of this research has been focused, mainly, on track tests. Different track or road methods have been developed for measurement of tyre/road sound emissions. The most important ones are the Coast-By, the Close-Proximity, the Statistical Pass-By or the Controlled Pass-By methods. Among all of them, the Coast-By method has been raised in Europe as standard method concerning the approval of tyres with regard to tyre/road sound emissions as preconized in UNECE Regulation 117 (2007)[2]. However, all the above mentioned methods have several disadvantages such as the influence of environmental factors, the different results that can be obtained depending on the test track or the vehicle upon which the tests are carried out, the lack of repeatability or, the most important aspect, which is the limitation of the measured magnitude, the sound pressure level. A new methodology (Clar-Garcia et al., 2016) based on drum tests and the ISO 3744 (1994), which was developed in order to avoid these limitations, has been proved to be comparable to the Coast-By (CB) method. This paper describes how different tyres have been tested according to both the CB and the new Alternative Drum test method (A-DR) while their results have been compared. In order to be able to carry out this comparison, as the measured magnitudes and test conditions differ widely from one test to another, the standardised ISO 9613 sound propagation method (ISO 9613-2, 1996) has been applied to obtain the sound pressure value at 7.5 m from the sound power level of a tyre measured under laboratory-controlled conditions when rolling against a drum. Results have shown that both methods are not only comparable but also have remarkably similar sound spectra and, for that reason, the new methodology based on drum tests can be used in order to obtain tyre/road noise emission approved values. [ABSTRACT FROM AUTHOR]

Highlights • Experimental validation of global active noise control using Modal FxLMS algorithm is carried out. • Experimental study on a rectangular box vibro-acoustic cavity under the presence of acoustic and structural distrubances using one and two control loudspeakers is presented. • Modal secondary paths are experimentally identified. • Modal control at a cavity-controlled and a panel-controlled resonance is presented. • Modal control with different choices of modes under control is carried out. Abstract The Modal FxLMS algorithm is recently proposed for reduction of global level of noise in vibro-acoustic cavities. The algorithm minimizes acoustic potential energy expressed in modal domain which allows a choice of acoustic modes whose modal amplitudes are desired to be minimized. The working of the algorithm and its effectiveness has been demonstrated previously through a numerical study and an experimental study is required to test the effectiveness of the algorithm in practice. To meet this objective this paper presents an experimental study of this algorithm for global active noise control in a rectangular box cavity. The algorithm utilizes modal filtered reference signals and modal amplitudes of the selected acoustic modes of the cavity. To identify modal filtered reference signals, modal secondary paths are utilized. In the present study, modal secondary paths are identified using experimentally identified physical secondary paths and acoustic mode shapes. Modal amplitudes of the acoustic modes are identified on the basis of acoustic pressure measurements from eight microphones suitably placed throughout the cavity. The performance of the algorithm is studied under the presence of acoustic and structural disturbances using one or two control loudspeakers. The active control is carried out at harmonic frequencies coinciding with cavity-controlled resonances and panel-controlled resonances. It is found from the experimental results that the Modal FxLMS algorithm is successful in reducing modal amplitudes of the selected acoustic modes. When all the significantly contributing acoustic modes are chosen, a reduction in global level of noise is observed at cavity as well as panel controlled resonances. [ABSTRACT FROM AUTHOR]

Abstract The operation of compressor at lower mass flow rates is limited by surge which is marked by large fluctuations in operational variables and accompanied by significant increase in noise. Ported shroud casing treatment is a widely used method to control the flow near unstable conditions in order to obtain a stable operation and enhance deep surge margin. The research on the acoustic effects of the ported shroud design is limited. Therefore, this paper numerically characterises the acoustic features of a turbocharger compressor with ported shroud design operating at marginal or soft surge conditions and investigates the correlation between acoustic characteristics and the spatial flow structures. The acoustic and the flow field features are analysed using spectral signatures obtained from an experimentally validated numerical model using both performance and acoustic measurements. Propagation of the frequency content through the ducts has been estimated with the aid of the beamforming and method of characteristics to enhance the content coming from the compressor. Expected acoustic phenomena such as rotating order tones and blade passing peaks are correctly identified in the modelled spectrum with the limitation to capture the specific broadband features. Hence, the numerical model can be used to further the research encompassing the impact these flow enhancement solutions have on the noise emission of the turbocharger. Inspection of the flow field shows radially exiting fluid at the ported shroud slot leading to the formation of the high-speed jets exiting the ported shroud cavity. Circumferential propagation of the stall cells is also identified in the impeller. Further inspection of the pressure field through modal decomposition implies the localisation of the energetic noise sources in the impeller downstream components. The influence of the ported shroud cavity on the acoustic characteristic of the compressor is not significant and is limited to the propagation of the tonal noise in the direction of impeller upstream. [ABSTRACT FROM AUTHOR]

Abstract Ambient environment noise can affect speech intelligibility in phone communication. This paper investigates the feasibility of increasing speech intelligibility in monaural hearing by adding noise at the other ear. The testing materials were generated by mixing the speech from the English Coordinate Response Measure corpus with three types of environmental noise, where 4 signals to noise ratios in the speech ear and 14 noise levels in the contralateral ear were included. The experimental results show that a proper level of contralateral noise can improve the speech intelligibility when the signal to noise ratio in the speech ear is lower than a certain level, but a large contralateral noise level has the opposite effect. A preliminary explanation for the phenomena is attempted by using a binaural loudness model and some psychoacoustic and physiological facts. [ABSTRACT FROM AUTHOR]

Abstract Nowadays, society has the need for air transportation all around the world. The yearly increase in the number of passengers forces airports to operate to a maximum of their capacity. This leads to an augmentation of the fleet of each airline and consequently to an increase in aircraft noise emissions. Accordingly, procedures for measuring aircraft noise levels have been developed. There are international standards that specify how transport noise (aircraft, traffic and railroad) must be measured. ISO 1996-2 standard has an appendix called Annex B which specifies the reference position of the microphone to undertake the measurement, and simplified correction factors to use in case that the measurement must be located near a reflecting surface (3 dB) or directly over a reflecting surface (6 dB). A façade behaves like a reflecting surface and the correction factor to apply is relevant to the study of noise because with the reflections produced on the outside of a building, people nearby can be affected. Therefore, numerous studies verifying the correction factors of ISO 1996-2 Annex B have been performed on façades, particularly for traffic noise. Most of the findings from these studies demonstrate that features of the source-receiver geometry change the correction factor. However, this correction factor has not been tested yet for aircraft noise whose source-receiver geometry differs from that of traffic noise. This paper intends to test the correction factor for aircraft noise on façade. It also tries to determine which relationship can be found among the noise level at the reference position and features like the façade noise level, source-receiver geometry and flight type. [ABSTRACT FROM AUTHOR]

Highlights • A new method is proposed to predict full-spectrum HST interior noise directly. • Wheel-rail noise sources are extracted with sound scattering effect considered. • Aerodynamic noise sources are calculated by the hybrid method (RANS/NLAS). • Predictions are in better agreement with measurements in whole frequency bands. • The deviations of OASPL are much smaller compared with other prediction methods. Abstract The high-speed train (HST) interior noise in low, middle and high frequency bands is predicted in different simulations due to the limitations of current numerical methods. In this paper, a new method named statistical vibration and acoustic energy flow (SVAEF) is proposed to predict full-spectrum HST interior noise directly. In the SVAEF theory, interior noise is solved in the form of energy flow, and panel vibration responses caused by mechanical and acoustic excitations are assumed to satisfy the linear superposition principle. The acoustic energy of exterior sound sources is mainly attenuated by the carriage structure in the equivalent form of sound transmission loss, while the mechanical vibration energy flows inside carriage structure and interior acoustic cavities. The interior acoustic responses are calculated under a dynamic equilibrium of the whole energy flow. Initially, a HST carriage model is established based on SVAEF theories. And all the subsystem parameters and exterior excitations are acquired properly through the measurements, simulations and empirical formulas. Among them, inverse-fast Fourier transform (IFFT) and rigid multi-body dynamics are used for track irregularity excitations and contact force, while the wheel-rail rolling noise is extracted and verified with the sound scattering effect of carriage surfaces considered. The distributions of aerodynamic noise are calculated by the hybrid method of Reynolds-averaged Navier-stokes (RANS) and non-linear acoustic solver (NLAS) approach with the pantograph system, the bogie and windshield completely considered. In addition, the equipment noise under the carriage is measured as one of acoustic excitations and the vibration of carriage panels is measured to extract mechanical excitations. Finally, the interior noise is predicted through SVAEF and compared with the measurements and other prediction methods. The results indicate that the trend of SVAEF predictions is in better agreement with measurements in the whole frequency bands, and the deviations of overall sound pressure level (OASPL) are much smaller. In conclusion, the effectiveness and accuracy of SVAEF method have been verified in the full-spectrum prediction of HST interior noise. [ABSTRACT FROM AUTHOR]

Abstract Due to improvements on combustion-engines and electric-engines for cars, tyre noise has become the prominent noise source at low and medium speeds. Models exist that simulate the noise produced by a rolling tyre, as do models that auralize different traffic situations from a basic data set. In this paper, an established model for tyre noise (SPERoN) is combined with an auralization tool. The combined model can predict the spectrum of the sound at 7.5 m, as well as reproduce the sound for a given listener position. The auralization uses a methodology where recorded sounds are converted to source signals for engine and tyre/road-interaction. These can be shaped by the spectra estimated in SPERoN and synthesized back into a pass-by signal. Psychoacoustic judgements were used to compare the modelled signals with recorded signals. To see how well the modelled signals match the real recorded signals for perception, two listening-tests were performed. The simulated and recorded signals were rated by pleasantness, loudness, roughness and sharpness using semantic differentials. It was found that responses for simulated and recorded signals correlate for all cases, but rankings could not be reproduced exactly. The model can be further improved to be more applicable for listening tests. [ABSTRACT FROM AUTHOR]

Abstract: Main goal of this paper was to describe an innovative method of noise prediction based on Genetic Algorithms. First part of the paper addresses the problem of growing noise, mainly in the context of a unified method for measuring noise. Further, Genetic Algorithms are described with regards to their fundamental features. Further a description is provided as to how Genetic Algorithms were used in the area of noise modeling. Next chapter shows results achieved with prototype software created for the purpose of research experiments. Finally, a practical technical application of this method is presented. [Copyright &y& Elsevier]

Abstract: There are four main air-related noise generation mechanisms at the tyre/road interface, which were all categorised more than 20years ago. The first one is the so-called ‘air pumping’ mechanism. Two other air-related phenomena that occur when there are air movements near the contact patch of the tyre are ‘air resonant radiation’ and ‘pipe resonances’ which appear at the footprint of the tyre. In addition to these, there is a forth effect, which is mentioned in the literature, that is occurring due to turbulence effects of the air surrounding the spinning tyre. There has been less focus on the air-related mechanisms than on other types of tyre noise generation mechanisms. This paper attempts to add some detail to current understanding of the air-related noise generation at the tyre road interface and gives some further information on how to identify the differences due to these mechanisms. Specifically in the present paper, a solid rubber tyre running on a vehicle chassis dynamometer is used to study the first two mechanisms. This is done with emphasis on the time history of the recorded signal and not on the frequency spectrum, as is more commonly used. A comparison with existing theoretical models of these mechanisms reveals some of the strength and weaknesses of the current understanding of these phenomena. [Copyright &y& Elsevier]

• Evaluation indexes of powerful sound quality can be reduced to three dimensions. • Powerful sound are related to frequency component, order ratio, and linearity. • Powerful sound has one of the two features: order relay and frequency retention. The subjective impression of car driving is affected mainly by noise, so it is necessary to develop the car interior sound quality with different characteristics according to the market positioning of the vehicle. "Powerfulness" is a kind of sound quality characteristic during acceleration. However, its subjective evaluation method and key influence factors are still not precise and cannot effectively guide the car interior sound quality design. In this paper, the subjective evaluation method of powerful sound quality and the strategy of the car interior noise target during acceleration are studied. Firstly, the Factor Analysis Method is used to carry out Dimension Reduction Analysis on 50 pairs of antisense words describing "Powerfulness". The result shows that powerful sound quality can be evaluated from three orthogonal dimensions: "Trilling", "Richness", and "Smoothness". Secondly, in view of the disadvantages of normal semantic differential method that it is difficult to evaluate the accelerating noise with time-varying non-steady-state features accurately, the Continuous Assessment by Predefined Categories (CAPC) subjective evaluation method is applied to the subjective evaluation of 24 car interior sound samples with different sound quality characteristics during acceleration. The objective parameters of the sound samples is calculated and analyzed for their correlation with the subjective evaluation results. The results show that the three subjective evaluation dimensions are related to the frequency components, order ratio, and linearity of the sound samples, respectively. Thirdly, a development process for the target of powerful sound quality is presented, including writing sound modulation software and artificially synthesizing sound samples with different parametric characteristics. Through the audition and evaluation of synthesized sound samples, two powerful sound quality features, namely Order Relay and Frequency Retention, are proposed by statistical methods. The support vector machine model verifies the rationality of the proposed features. At last, the case of realizing the car interior powerful sound quality by tuning the intake system is discussed. The research in this paper can provide a reference for the sound quality design during acceleration in passenger cars. [ABSTRACT FROM AUTHOR]

Abstract: For many years the problem of noise generated by trains has had an increasing importance; in this paper, attention is focused on the noise generated by the train wheels due to their vibration. Today there are many kinds of railway wheels which are affected by different noise generation mechanisms. If the traditional and well known solid wheel is considered, a lot of data is already present in the literature both concerning the vibration and the noise point of view. On the other hand, the widely used resilient wheels are not so well known in their vibratory and acoustic behaviour as in the case of solid ones. The extensive experimentation presented and commented in this paper looks for a confirmation of some literature data first, and then it gives new results. Particularly the vibro-acoustic characterization of different kinds of wheels (both solid and resilient ones) has been carried out, in order to have a comparison between the behaviour of the newly built wheels and the older ones, representing the state of the art. Besides it has been shown that a detailed modal analysis of the suspended wheel coupled to sound measurements can give useful information about the wheel noise emission in its normal operating conditions. [Copyright &y& Elsevier]

Abstract: Magnetic resonance imaging (MRI) scanners can produce noise measuring over 130dB SPL. This noise stimulates the auditory nervous system, limiting the dynamic range for stimulus driven activity in functional MRI (fMRI) experiments and can influence other brain functions. Even for structural scans it causes subject anxiety and discomfort in addition to the impediment to communications. Here we describe the realization and validation of a sound system for sound presentation inside an MRI scanner and the modifications to a standard active noise control technique for use in the noisy and compact environment of the scanner. This paper provides a review of the technology available for the presentation of audio stimuli in an MRI environment and the modifications required for the active control of scanner noise. Some of the content has been previously published [Chambers J, Akeroyd MA, Summerfield AQ, Palmer AR. Active control of the volume acquisition noise in functional magnetic resonance imaging: method and psychoacoustical evaluation. J Acoust Soc Am 2001;110(6):3041–54; Levitt H. Transformed up–down methods in psychoacoustics. J Acoust Soc Am 1971;49:467–77], but this paper goes further in describing the stages of development as the system performance was optimised. The performance of the system and both the objective and subjective reduction of the scanner noise are reported. Finally, we discuss recent improvements to the system that are currently being evaluated and describe the theory of opto-acoustical transducers that operate on the principle of light modulation. These are immune from, and do not create, electro-magnetic interference (EMI) and radio-frequency interference (RFI). [Copyright &y& Elsevier]

This paper deals with the global reduction of axial flow fan noise in ducts in a building using a hybrid passive–active noise control method. The effectiveness of using an infra-red device as a reference signal source is also investigated. It is shown that using such a hybrid noise control system over an axial-flow fan reduces the overall sound pressure level by 5 dB(A) in the surrounding environment and global control of the blade passing frequency can also be achieved. This paper also shows that using an infra-red device as a reference signal source produces marginally better control as compared with using a microphone reference sensor. Moreover, long term stability is guaranteed and the possibility of acoustic feedback is eliminated. [Copyright &y& Elsevier]

Underwater acoustic target recognition based on ship radiated noise has always been a challenging task due to the complexity of underwater environment and the antagonism of targets. An underwater acoustic target recognition network based on S hip radiated N oise spectrum component A nalysis (SNANet) is proposed in this paper by extracting the spectrum features of each component in different frequency bands, which improves the recognition accuracy as compared with existing end-to-end recognition methods. Adaptive weight based on forward weight and backward weight is used to fuse main and auxiliary features. Experiments have demonstrated that SNANet surpasses currently existing models in performance on the public dataset DeepShip. • SNANet employs S hip radiated N oise spectrum component A nalysis to utilize frequency bands of each component. • The main and auxiliary features are fused with adaptive weights to obtain a robust feature. • SNANet demonstrates superior recognition performance on DeepShip compared to end-to-end methods. [ABSTRACT FROM AUTHOR]

• Novel approach to evaluate vehicle noise sub-source contributions. • Analysis based on first and second derivatives of noise emission curves. • Vehicles characterized by different motorizations were considered in the study. • Procedure tested for seven probe vehicles on flat roads. • Procedure replicated for three probe vehicles on a hilly road. In the last decades, car manufacturers have gathered efforts to lower vehicle noise emissions by acting on power-unit insulation and designing advanced mufflers. Moreover, the penetration rate of electric vehicles in the national fleet composition is increasing. As a result, the rolling noise contribution, which historically overclasses the other vehicle noise contributions starting from 40 to 50 km/h, could begin being relevant at lower speeds. Detecting the contribution of each sub-source to the overall vehicle can be challenging and costly due to the need for extensive measurement campaigns. Thus, this paper aims to investigate the aforesaid hypothesis through the analysis of the first and second derivatives of vehicles' noise emission curves which does not require broad data collection. Noise emission curves for seven probe vehicles, differently powered (namely, two diesel, two gasoline, two hybrid-electric, and one LPG), were obtained on flat road locations, and, for three of them, on a hilly road location. Subsequentially, the first and second derivatives of the noise emission curves were computed through the finite difference approach, to identify the speed regions where rolling noise contribution starts becoming predominant. Results showed that the rolling noise contribution is relevant for speeds lower than 40 km/h at flat roads, and it moves forward on the hilly road location. The analysis also revealed that differences in terms of noise emissions between hybrid and conventional vehicles are detectable in the speed range between 15 and 20 km/h, where the former category of vehicles could work purely in electric mode. [ABSTRACT FROM AUTHOR]

The acoustic vector sensor (AVS) has a wide application in the direction of arrival (DOA) estimation of sound sources including aircraft, underwater or on-land vehicles, search-and-rescue efforts, etc. The performance of only one acoustic vector sensor can compare favorably with a traditional acoustic array in DOA estimation. The anisotropic noise problem of the vector sensor has had a severe affective on the estimation accuracy and has caused little attention until now. In this paper, an AVS measurement system is designed, and an Anisotropic Sparse Bayesian Learning (SBL) method (the A-SBL method) is proposed to model and estimate the anisotropic noise of the AVS system. A high-resolution DOA estimation method is also introduced based on the noise estimation algorithm. The experimental results exhibit the necessity of modeling the anisotropic noise, and the estimation accuracy of the proposed A-SBL method based on the noise model is verified. The comparison of DOA methods shows the superiority of the proposed method, in which the DOA estimation error is not more than 1 °. The proposed method's utility may be found in applications for localization or tracking of targets with prominent acoustic characteristics when the environment is complicated. [ABSTRACT FROM AUTHOR]

This paper deals with tyre noise indoor tests in a semi-anechoic chamber and with the identification of a monopole substitution model suitable for simulating the deterministic part of the sound field generated by a rolling tyre. The first part of the paper illustrates the test procedure and the data processing methodology adopted for separating the deterministic contribution to tyre noise, i.e. that mainly related to tread pattern, from the random one. In the second part, the monopole substitution model is presented, together with the results of model identification and sound field simulation. The results reported in the paper for two commercial tyres (with the same size and similar structural characteristics, but with different tread pattern design) show how the predominance of the deterministic/random noise contributions varies with frequency and confirm the random noise spectrum to be substantially independent of the specific tread pattern. With reference to the monopole substitution model, its capability of reproducing the acoustic field radiated by a rolling tyre is assessed through the analysis of both sound spectra and space distribution. [ABSTRACT FROM AUTHOR]

This paper presents an efficient reduction method for predicting the nonlinear transient and steady state squeal events in mechanical systems subjected to friction-induced vibration and noise. This proposed reduction technique is based on the Double Modal Synthesis (DMS) method that involves the use of a classical Craig & Bampton modal reduction on each substructure considering the interface surfaces associated to a condensation at the frictional interface based on complex modes. In this paper, the performances of some reduced bases based on the DMS strategy are investigated in the case of a finite element model of a simplified disc/pads system. The originality of the present work is to propose a comprehensive study on the convergence of the DMS method in order to predict not only the stability or the limit cycles of a simplified brake system but also the transient nonlinear self-excited vibrations, as well as the squeal noise. A special attention is brought to the convergence of the DMS method and more precisely the number of interfaces modes required to provide satisfactory results in regard to various criterion used to characterize the squeal. [ABSTRACT FROM AUTHOR]

Aiming at the common problems of the engineering vehicles with high environment noise and poor acoustic comfort, this paper proposes an acoustic comfort subjective evaluation method based on rank score comparison (RSC) and develops a corresponding software system; it provides the solution method of evaluation modeling and improvement measure based on multiple linear regression (MLR). The actual application case of 50 noise samples from forklifts is presented to verify the feasibility and effectiveness of the RSC method. Through the subjective evaluation experiment, calculation of psychoacoustic parameters and data statistical tests, acoustic comfort evaluation model is established based on MLR. Consequently, the most significant parameter and improvement measure of acoustic comfort are obtained by means of sensitivity analysis and noise spectrum analysis. Finally, the improvement test of a target prototype is carried out and results indicate that the acoustic comfort has been improved obviously and the noise decibel level has met the industry standard requirement. [ABSTRACT FROM AUTHOR]

Diesel combustion noise has become a crucial aspect for the engine manufacturers due to its impact on human health and influence on the customer purchasing decision. The interaction of the pressure waves after mixture self-ignition induces cavity resonances inside the combustion chamber. This complex phenomenon produces high-frequency pressure oscillations, hence traditional in-cylinder measurements do not provide enough information to characterise the in-cylinder acoustic field. In this paper, a numerical methodology is proposed for assessing the Diesel combustion as a noise source and to overcome measurement limitations. An optimisation procedure is also presented in order to determine the numerical calculation parameters, boundary conditions definition and initialization. Results show that local flow conditions at the start of combustion have a strong influence on the acoustic response of the in-cylinder noise source. These particular conditions are only achievable by the proposed methodology which considers entire engine cycle simulations with the complete cylinder domain. Therefore, traditional Computational Fluid Dynamic (CFD) approaches, such those used for predicting combustion stability or pollutant emissions, are not suitable for reproducing the physical mechanisms of noise generation and they cannot be used for acoustic purposes. The reliability of the proposed methodology to simulate the acoustic field accurately inside the combustion chamber has been validated by comparison with experiments. [ABSTRACT FROM AUTHOR]

Cough detection has recently been identified as of paramount importance to fully exploit the potential of telemedicine in respiratory conditions and release some of the economic burden of respiratory care in national health systems. Current audio-based cough detection systems are either uncomfortable or not suitable for continuous patient monitoring, since the audio processing methods implemented therein fail to cope with noisy environments such as those where the acquiring device is carried in the pocket (e.g. smartphone). Moment theory has been widely applied in a number of complex problems involving image processing, computer vision, and pattern recognition. Their invariance properties and noise robustness make them especially suitable as “signature” features enabling character recognition or texture analysis. A natural extension of moment theory to one-dimensional signals is the identification of meaningful patterns in audio signals. However, to the best of our knowledge only marginal attempts have been made in this direction. This paper applies moment theory to perform cough detection in noisy audio signals. Our proposal adopts the first steps used to extract Mel frequency cepstral coefficients (time-frequency decomposition and application of a filter bank defined in the Mel scale) while the innovation is introduced in the second step, where energy patterns defined for specific temporal frames and frequency bands are characterised using moment theory. Our results show the feasibility of using moment theory to solve such a problem in a variety of noise conditions, with sensitivity and specificity values around 90%, significantly outperforming popular state-of-the-art feature sets. [ABSTRACT FROM AUTHOR]

The noise of electrical machines such as electric motors, power transformers and electrical inductors increasingly interested designers and manufacturers of several industries (automotive, rail, etc.). This interest concerns the reduction of noise caused by these machines in transportation vehicles for example, to provide better comfort to users. In this paper, the noise radiated by an electrical power transformer is predicted using an end-to-end multiphysics modelling solution. The modelling procedure is based on the chaining of three analysis methods. The first one simulates the electromagnetic problem which generates Maxwell forces on the magnetic core of the transformer from electrical excitation. These forces are considered as an input for the mechanical problem solved by the finite element method (FEM) to calculate the acceleration field on the structure. Finally, these accelerations are considered as in input for the acoustic model to compute the noise radiation using the Boundary Element Method (BEM). Two models of the ferromagnetic core are considered. The first is a bloc model where the different laminates are stuck and the second is a laminated model where a small sliding condition is introduced at interfaces between sheets of metal. Numerical results of the mechanical and acoustic models using a laminated core are compared with experimental data and show good agreements with measurements. [ABSTRACT FROM AUTHOR]

Typically, a component level approach is used in control of internal combustion engine (IC-engine) exhaust noise. This has enabled the development of new, cost-efficient silencers, for example. However, prediction of sound emission from a tailpipe or insertion loss of a silencer requires a more extensive, system level approach. Therefore, valid IC-engine source characteristics and a valid model of the whole transmission path are needed. When characterizing an IC-engine as a source with the commonly used in-duct multi-load method, the requirements for load impedance variation must be fulfilled. It is fairly easy to vary the load in automotive cases, whereas new methods must be developed for large IC-engines, used e.g. in power plants. In this study, the source data determination process is investigated in detail, a novel “capsule tube method” is developed further and used for experimental acoustic source data determination of medium speed IC-engine exhaust system in harsh environment. With suitable filtration and statistical outlier rejection methods presented in this paper, the source data of a test IC-engine exhaust system was derived with success. [ABSTRACT FROM AUTHOR]

This paper presents wind tunnel experiments to illustrate the effects of surface curvature on the aeroacoustic performance of airfoil E387. For the first time, surface curvature effects are considered in an investigation of the airfoil’s self-noise. To distinguish the effects of surface curvature, the CIRCLE method is applied to the airfoil E387 to remove slope-of-curvature discontinuities and the redesigned airfoil is denoted A7. Anechoic wind tunnel tests were performed with E387 and A7 at three low Reynolds numbers to investigate aeroacoustic performance by measuring airfoil self-noise at different angles of attack (AoA) and spatial positions. At 2° and 4° AoA, A7 presents a tone with a reduced amplitude compared with E387 due to its improved slope-of-curvature distribution. It is concluded that improving surface curvature distribution improves airfoil aeroacoustic performance. [ABSTRACT FROM AUTHOR]

This paper presents the work done to establish a methodology that is capable of predicting tonal noise generation in high speed centrifugal fans. The deliverables from this work emphasize on identifying and characterizing the source of tonal noise in the centrifugal fan. Computational fluid dynamics (CFD) modeling was performed using 3-D Detached Eddy Simulation (DES) to compute the unsteady flow field in the fan. The calculated time history of surface data from the CFD is then used in Ffowcs Williams-Hawkings (FW-H) solver to predict the far field noise levels. The predicted aerodynamics and aeroacoustics results are in good agreement with the experimental data acquired from the flow testing facility and the anechoic chamber. The study conducted on the centrifugal fan shows that the aerodynamic interaction between the non-uniform impeller outflow and the leading edge of the diffuser vane is the source of tonal noise generation. The impingement of the jet-wake flow structure from the impeller outflow causes periodical pressure fluctuation on the leading edge of the diffuser vanes which leads to the tonal noise generation at the blade passing frequency (BPF). [ABSTRACT FROM AUTHOR]