bluuebunny/crossref_metadata_2025 huggingface dataset:
European Aircraft Noise Research Network (X3-Noise)
Authors: Collin Dominique
Published: May 2008

The X3-NOISE Coordination Action, through its network structure and comprehensive workplan involving expert groups, scientific workshops, stakeholder seminars and a common information system, addresses the aircraft noise challenges set by the ACARE 2020 Vision. To this end, X3-Noise undertakes the elaboration and coordination of research strategies, the dissemination of results and the integration of European research activities in the field of air transport related to noise. Over 4 years, the project involves 32 partners from 20 countries (FR, UK, ES, NL, BE, DE, SE, IT, PL, HE, HU, CZ, LT, IE, PT, RO, CH, UA, EG, BR), combining the complementary skills and expertise of industry partners, SMEs, university and research establishments to cover the whole field of interest. The international co-operation aspects of the research agenda to be developed through the project activity are further reinforced by the participation of 3 partners from Ukraine, Egypt and Brazil acting as Focal Points at Regional level.
Reducing aircraft noise during approach and departure by efficient operations
Authors: De Muynck Robert J.
Published: May 2008

Reducing the noise from aircraft around airports is a serious challenge. Apart from making the noise source, the aircraft, more silent, by advanced engines and aerodynamics, additional noise reduction can be achieved by moving the noise source away, as well as by a more silent operation of the aircraft. One of these innovative approach procedures is the Continuous Descent Approach. The principle is that aircraft approaching an airport follow a continuous descent profile at low thrust setting instead of making gradual altitude steps. The higher altitude and the lower thrust of the aircraft allow decreasing significantly noise exposure around the airport. First results show considerable noise reduction from 3dB to 8dB compared to conventional practices. Additionally, this procedure allows reducing fuel consumption and emissions. To make CDA procedures operationally feasible however, efforts are needed to develop *CDA operating procedures so that they can be flown in busy traffic *improved onboard systems to fly the CDA *accurate planning and sequencing tools for air traffic controllers *better interaction and interoperability between aircraft and air traffic control systems The presentation will discuss progress made in EU projects such as Sourdine II, OPTIMAL and ERAT.
Effective protection of the sense of hearing is prevented by ISO1999 noise standard
Authors: Fleischer Gerald
Published: May 2008

To determine auditory performance in a simple way, pure-tone audiometry is being used. While health-related diagnostics is generally becoming more and more refined, ISO1999 is demanding rather rudimentary procedures. Both, frequency range and number of test frequencies are reduced, making it impossible to use modern and effective analytical tools such as pattern recognition. There is a clear relation between pressure-time-history of impulses and the details of the resulting auditory damage. But this relation can only be recognized if the restrictions of this standard are being ignored. Typical examples of audiograms from a large data base will be presented, showing simultaneously the data according to ISO1999 and in more modern ways. It will also be demonstrated how useful the tool of pattern recognition can be, for analysis of damages, as well as for preventive measures.
Comparison of impulse noise damage risk criteria using the Albuquerque blast overpressure walkup study data
Authors: Murphy William J. , Khan Amir , Shaw Peter B.
Published: May 2008

The 1968 CHABA recommendations to limit impulsive noise exposure to levels below 140 dB SPL form the basis of current United States occupational and military standards. The U.S. military standard, MIL-STD-1474D, estimates the number of allowable shots to which a person may be exposed using peak level, B-duration, for varying levels of hearing protection usage. The European Union upper limit peak exposure action level is 137 dB C-weighted for the unprotected ear and 140 dB C-weighted for the protected ear. The U.S. Army blast overpressure studies in the early 1990's investigated the effects on the hearing of soldier subjects of simulated weapon blasts with varied levels and A-durations. The hearing thresholds of the subjects were tested before and after exposure to blasts. Exposures ranged from 6 shots to 100 shots per day and levels from 173 to 195 dB peak SPL. As judged by information criteria (AIC, BIC), the LAeq8 index with unprotected data yielded the best fit to logistic models; all the indices produced a better fit with unprotected data than with protected data. Other metrics including the MIL-STD-1474D and the Auditory Hazard Assessment Algorithm for Human were evaluated and will be presented in this paper.
Empirical evaluation using impulse noise of the level-dependency of various passive earplug designs
Authors: Berger Elliott H. , Hamery Pascal
Published: May 2008

An objective in the development of hearing protection devices (HPDs) has been the design of a passive earplug that provides modest or no attenuation at low sound levels, with greater protection at high sound levels. This raises the issue of not only how to construct such a device, but also how to evaluate it. There is the related question of whether conventional HPDs are actually level independent. Passive level dependency is typically accomplished via an orifice that causes sound transmission to decrease as input level increases. We utilized an impulsive noise source (explosives) with peak levels from 110 to 190 dB SPL to measure the insertion loss of a variety of commercially available and developmental earplugs. The tests were conducted at frontal incidence in a reflection-free outdoor environment using the Institute of Saint-Louis acoustical test fixture specifically constructed for HPD attenuation measurements. Conventional foam and premolded earplugs exhibited attenuation that was essentially constant with level, whereas the best of the level-dependent designs provided attenuation that increased by about 25 dB over the 80-dB range of test impulse levels. This latter design has been successfully utilized since 2000 in the Combat Arms™ Plug widely fielded in the U. S. Military.
Time domain modeling of acoustic propagation with acoustic wave propagator and absorbing boundary conditions
Authors: Ehrlich Jan H.
Published: May 2008

The acoustic wave propagator (AWP) is the application of the time evolution operator on the acoustic wave equation for stationary systems in a polynomial expansion of Chebychev polynomials. It allows to increase the time step by more than one order of magnitude compared to finite difference time domain (FDTD) codes. In contrast to other implementations of the AWP the spatial differentiation is carried out with finite difference techniques because this allows the use of the perfectly matched layer formulation as absorbing boundary conditions. The formulation includes the direct implementation of acoustic sources with sinusoidal time evolution. Other sources can be synthesized by their Fourier components. For the calculation of large areas the explicit formulation of a large system matrix can be avoided by calculating the propagation equations for each time step at row and column level repeatedly which reduces memory requirements notably. This procedure and the suitability of the finite difference approach for parallelization makes the extension to fully three dimensional calculations possible. Examples for benchmark problems with sound propagation in air and water are given.
An eigenfunction expansion method to efficiently evaluate spatial derivatives for media with discontinuous properties
Authors: Hornikx Maarten , Waxler Roger
Published: May 2008

Pseudo-Spectral methods are often used as an alternative to the Finite Difference Time Domain (FDTD) method to model wave propagation in heterogeneous moving media. The FDTD method is robust and accurate but is numerically expensive. Pseudo-Spectral methods make use of the wavelike nature of the solution to obtain more efficient time-domain algorithms. The most straightforward of the Pseudo-Spectral methods is the Fourier method in which a spatial Fourier transform is used to evaluate the spatial derivatives in the wave equation. Whereas this method is accurate for a weakly heterogeneous moving medium, it degenerates for media with discontinuous properties. The eigenfunction expansion method presented here is a way to accurately and efficiently evaluate spatial derivatives in media with interfaces. As in the Fourier method, transforms may be calculated using FFT's and spatial sampling is limited only by the Nyquist condition. The performance of the method is shown in a time-domain implementation for media with discontinuous density and sound speed.
Trim FEM simulation of a dash and floor insulator cut out modules with structureborne and airborne excitations
Authors: Duval Arnaud , Baratier Julien , Morgenstern Christian , Dejaeger Ludovic , Kobayashi Norimasa , Yamaoka Hiroo
Published: May 2008

During a vehicle development, measurements on cut out modules in large coupled reverberant rooms are often carried out in the middle and high frequency range in order to optimize the insulation performance of the trims (Transmission Loss). Using optimal controlled mounting conditions, we have been able to extend the frequency range to the low frequencies in order to validate trim FEM models of a dash and floor insulator modules with structureborne and airborne excitations. Both coupled response with movable concrete cavities (structureborne excitation) and Transmission Loss with the coupled reverberant rooms (airborne excitation) have been measured and simulated for various types of insulators on the same setup, without any change on the mounting conditions. An additional movable absorbing environment in the large reception room has been deployed in order to carry out laser vibrometer (skeleton velocity) and p-u probes (particle velocity and intensity) measurements on the surface of the trims. By incorporating the maximal treatment mock-ups of the cut out modules as additional trims in the models, we have obtained good correlation results between measurements and simulations for both bare and trimmed configurations for a dash and floor insulators with structureborne and airborne excitations.
Practical aspects of implementing car interior active noise control systems
Authors: Schirmacher Rolf , Lippold Roland , Steinbach Frank , Walter Florian
Published: May 2008

When implementing real-world, close-to-production active noise control (ANC) systems for car interiors, many aspects far beyond textbook theory have to be taken into consideration -- many of which might also be left out for first demonstrator systems. Due to the predominant role of robustness and reliability, any kind of uncertainty in the system has to be considered carefully. Among others, the uncertainties and changes of the acoustical environment, e.g. due to temperature changes, number of passengers, open windows and also of system components, e.g. loudspeakers and microphones have to be measured and/or modeled. This also gives some new insight into the acoustical environment inside cars at low frequencies. In addition, the quality of input data (e.g., the update rate for rpm information) is of major importance for the acoustical performance in terms of noise reduction. Finally, stability analyses and robustness calculations must be extended to incorporate uncertainties as well as time domain effects even for more or less freqency domain problems like engine noise. This requires to re-formulate feed-forward systems as feed-back systems and calculate system responses. Measurement results on the interior acoustics (and its uncertainty) as well as additional developments on ANC system robustness will be presented.
Fluctuations under turbulent flows: Enhanced methods for separation of propagative wavenumbers from wall pressure dataset
Authors: Debert Sébastien , Pachebat Marc , Valeau Vincent , Gervais Yves
Published: May 2008

This work is a part of a more general study on automobile interior noise due to acoustic and aerodynamic wall-pressure fluctuations. Using experimental data of wall-pressure fluctuations measured with a microphone array beneath several kinds of flows, a wave-number analysis based on recently developed signal processing methods -- the spatial Empirical Mode Decomposition (sEMD) and the Ensemble Empirical Mode Decomposition (E-EMD) -- is carried out, in order to separate acoustic and aerodynamic pressure fluctuations. In opposition with an existing classical method previously used, based on the spatial correlogram, these methods do not require a stationary uniform flow. A turbulent boundary layer on a flat plate and a detached/reattached flow downstream three different forward-facing steps are tested, with flow velocities from 0 to 40 m.s-1, with or without a well-controlled artificial acoustic source. The sEMD method is first used as a wavenumber filter, and is shown to improve the detection of acoustic fluctuations of about 5 dB on classical wavenumber (k,f) representations. The E-EMD method is developed in order to decompose the (x,t) representation to make possible the separation of the acoustic and aerodynamic components, regardless of the stationarity or the uniformity of the flow.
Prediction of the Excitation Force Based on the Dynamic Analysis for Flexible Model of a Powertrain
Authors: Kim Yoon Sug , Kim Sung Jong , Song Min Geun , Lee Sang Kwon
Published: May 2008

The powertrain is one of the import sources for the interior noise. In order to predict the interior noise due to a powertrain, the experimental method is has been used based on the TPA (transfer path analysis). Although this experimental method is a useful tool for the identification of the noise source and the transfer path due to the powertrain, it is difficult to modify the structure of a powertrain by using the experimental method for the reduction of vibration and noise. In order to solve this problem, the paper presents the noble approach for the prediction of interior noise caused by the vibration of the powertrain based on the hybrid TPA (transfer path analysis) technology. Therefore, the vibration of the powertrain in a vehicle is numerically analyzed by using FEM (finite element method). The vibration of the other part in a vehicle is investigated by using the experimental method based on VATF (vibrato-acoustic transfer function) analysis. These two methods are combined for the prediction of interior noise caused by powertrain. This paper present the prediction of the excitation force of the powertrain to the vehicle body based on numerical simulation.
A transversal substructuring modal method for the acoustic analysis of dissipative mufflers with mean flow
Authors: Albelda José , Denia Francisco D. , Fuenmayor F. Javier , Martínez Manuel J.
Published: May 2008

This work presents a modal approach to evaluate the transversal modes and wavenumbers for dissipative mufflers with mean flow. The method is based on the division of the transversal section of the muffler into subdomains, for which two simple sets of modes are considered. The first set of modes satisfies the condition of zero pressure at the common boundary between subdomains, while the second fulfils the condition of zero derivative in the direction normal to this boundary. From these sets, a substructuring procedure is applied that provides the final modes of the complete cross section, considering the presence of absorbent material, a perforate and mean flow. The technique avoids iterative schemes associated with the nonlinear characteristic equation found, for instance, in the analytical modelling of perforated dissipative circular mufflers. Once the final transversal modes have been calculated, the mode matching technique is applied at the geometrical discontinuities to completely define the acoustic field inside the muffler. The acoustic attenuation is then predicted by means of the transmission loss. Comparison with finite element calculations and results available in the literature show good agreement. The attenuation of some selected mufflers is analysed, including the effect of the perforate and the mean flow.
Prediction of sound transmission through automotive door seal systems
Authors: Andro Bertrand , Chaigne Sébastien , Diallo Alpha , Mermet Matthieu
Published: May 2008

In automotive industry the door seal systems is an important contributor to vehicle interior noise in the middle and high frequency range. The aim of the study was to develop a numerical model in order to predict the sound transmission loss through elastomeric seals. At the early stage of the development process, this type of numerical tool is very interesting to investigate the influence of the design parameters of the seal. Two steps were necessary: a static analysis to calculate the seal shape after compression (door closure event), an acoustic analysis based on dynamic parameters to determine the sound transmission. Finite element methods were used for both steps (commercial softwares). These two steps were validated experimentally for two types of geometry, different compression ratios and loading cases. One original contribution of the paper concerns the determination of a valid non-linear model for the static part and of a good approximation of the dynamic behavior of the elastomer's Young modulus. Finally, a sensibility analysis was performed in order to evaluate the influence of the design parameters of the door seal system such as the compression ratio or the dynamic parameters.
A review of the use of different noise prediction models for windfarms and the effects of meteorology
Authors: Parry Graham
Published: May 2008

As a result of involvement in a specific wind farm development at Guestwick, Norfolk and a requirement to determine the efficacy of competing noise prediction models a review of the potential impacts of a six-turbine wind farm was carried out. The paper considers the results of comparing three specific noise prediction methods and algorithms and determines the extent to which adherence to either one of the methodologies could result in relatively large differences in predicted noise levels under varying wind conditions and accordingly the potential for differing conclusions being reached as to the acceptability of the wind farm with respect to the ETSU-R-97 assessment methodology. The paper also examines other noise modelling research carried out on behalf of ETSU.
Models of natural background noise and masking of wind turbine noise
Authors: Bolin Karl
Published: May 2008

Wind turbine (WT) noise limits adjusted to background noise levels are used in several countries among others Britain and France. To determine the background noise level extensive measurements at locations near the proposed WT site are performed. This paper present methods to avoid these measurements in woodland and coastal areas, it also include a pre-study concerning the audibility of WT noise when mixed with background noise. A prediction model for noise from vegetation is described. This has been coupled to wind field simulations and fluctuations of vegetation noise can therefore be predicted. Measurements and a model for sea wave noise are also presented. Furthermore the paper present results from psycho acoustic tests with 8 subjects. These involve hearing thresholds and partial loudness when WT noise is mixed with background noise. These are compared to two loudness models. Two different WT sounds have been used as stimuli. The first sound is from a single WT and the second sound is from a WT park. Results show how natural background noises influence the audibility of WT noise and could be used as a tool to optimize the power generated from WTs without causing disturbance among nearby residents.
Response to wind turbine noise in the Netherlands
Authors: Pedersen Eja , Bouma Jelte , Bakker Roel , Van Den Berg Frits
Published: May 2008

A cross-sectional study with the objective to explore the impact of wind turbine noise on people living in the vicinity of wind farms was carried out in the Netherlands in 2006. A postal questionnaire assessing response to environmental exposures in the living area, including wind turbine noise, was answered by 725 respondents (response rate: 37%). Immission levels of wind turbine noise outside the dwelling of each respondent were calculated in accordance with ISO-9613. The risk for being annoyed by wind turbine noise outdoors increased with increasing sound levels (rs = 0.501, n = 708, p<0.001). The risk for annoyance was decreased for respondents who could not see wind turbines from their dwelling and for respondents who benefited economically from the turbines. No statistically significant correlations between immission levels of wind turbine noise and health or well-being were found. However, noise annoyance due to wind turbine noise was associated with stress symptoms, psychological distress and lowered sleep quality.
Laboratory assessment of noise annoyance from large wind turbines
Authors: Pedersen Steffen , Mo/ller Henrik
Published: May 2008

An investigation of the annoyance from the wind turbine noise, to which neighbors may be exposed, is carried out. The aim is to obtain dose-response relationships and to uncover if specific noise components (e.g. low-frequencies) are primary contributors to the annoyance. In the experiments, sounds recorded close to large wind turbines are filtered (and levels adjusted accordingly) to represent indoor and outdoor positions at the neighbors' dwellings and played back in the laboratory. Challenges relating to the recording and transformation of sounds are discussed. The exposure technique is a combination of an advanced low-frequency chamber that can reproduce the frequency range 2-250 Hz (with uniform distribution in the room) and additional loudspeakers for the higher frequencies. The listening test is a randomized design. The stimuli, of 10 minute duration, are presented at three levels and in combinations of filtered versions (low- and mid-frequency) such that the influence of low-frequency tonal components and level fluctuations is investigated. 25 subjects are exposed to the stimuli while reading a novel and afterwards they rate annoyance on a visual analog scale.
Overview of turbofans noise prediction methods based on CFD computations
Authors: Morel Cédric , Farvacque Benoit
Published: May 2008

Overview of turbofans noise prediction methods based on CFD computations The constant trend to increase bypass ratio in turbofan aircraft engines has led to an increase of the relative contribution of rotors to the overall engine noise. There is therefore a need for efficient and accurate prediction tools to achieve a silent design of the rotor components. Here is given an overview of the different aeroacoustic methods investigated by Snecma and used for prediction of tone interaction noise, broadband interaction noise and broadband fan self noise. Different levels of methods refinement, from various analytical models to steady and unsteady CFD, will be compared in terms of accuracy of prediction and computational cost. Examples of implementation of these methods on conventional turbofan and counter-rotating fan configurations will be presented.
Benchmark of fan noise propagation tools
Authors: Mardjono Jacky
Published: May 2008

Various propagating codes based on different formulations have been developed over the last years to simulate the fan noise propagation into the nacelle of a turbofan engine and its radiation in the Far field. The abilities of the ACTRAN softwares (Potential formulation / FEM), SPACE (Linearised EULER equations / DGM) and ICARE (Rays-tracing method) to simulate typical industrial configurations in the frequential domain have been evaluated based on measurements carried out at the RACE acoustic test facility on a fan model at 1/2 scale. The results of the computations carried out with each of these codes on intake and exhaust configurations (axisymmetric assumption) in hard wall and lined duct will be compared to the measured far field directivities. These comparisons will be discussed depending on the establishment of patterns (sources types, mean flows types, boundaries conditions) considered in the simulations of each of these codes. The impacts of the considered convected mean flow types (Uniform, Euler, NS,...) and the capacities of these codes to predict noise attenuation of the treatments will be investigated in particular.
Validation of Thickness and Loading Noise Codes by Isom's Formula Applied to Subsonic Axial and Centrifugal Fans
Authors: Khelladi Sofiane , Fedala Djaafer , Bakir Farid , Rey Robert
Published: May 2008

The thickness noise predicted by the Ffowcs Williams and Hawkings (FW&H) equation depends on the normal velocity vn which is very sensitive to the meshing size. Isom showed that in far field a monopolar source is equivalent to a dipolar source induced by a uniform distribution of the load on the entire moving surface. Consequently, the calculation of the thickness noise becomes completely independent of the normal velocity vn. Its expression, as suggested by Farassat, is for any moving surfaces. The main objective of this paper is to determine a specific expression of Isom's thickness noise in time and frequency domains for axial and centrifugal subsonic fans. The scope of the proposed expression of Isom's thickness noise is threefold: (1) highlight the effect of each geometrical parameter of the fan on the overall thickness noise, (2) a fast computational mean and low memory storage capability since the acoustic pressure in frequency domain is calculated for only one blade, and (3) a benchmark test of consistency for thickness and loading noise codes in both time and frequency domains when using the free field solution of FW&H's equation.
Prediction of the tonal noise radiation of an axial flow fan located downstream of a Bluff Body
Authors: Gault Richard , Cooper Richard K. , Wang Jian , Schram Christophe
Published: May 2008

This paper investigates the tonal noise radiated by a subsonic axial flow fan when installed downstream of a bluff body. Typically industrial axial flow fans operate in cluttered environments, and are usually driven through direct coupling from an engine. For this investigation, the fan is located in a knife-edged shroud and placed downstream of a bluff body having representative dimensions of a typical engine. Axial flow fans in general radiate broadband and discrete frequency noise, the latter of which modelling efforts are maturing. The numerical simulation is based on the aero-acoustic analogy where the unsteady flow is first computed using CFD and then passed to a BEM solver to compute the acoustic radiation. URANS and DES methods are examined for the turbulence modelling. The time-varying force on a single blade in the CFD solver over one complete rotation is used to construct the equivalent fan source in the BEM model. Experimental measurements of Sound Pressure Level are performed in a hemi-anechoic chamber, and a comparison between numerical predictions made. This numerical procedure can be used to further aid designers in understanding the effects of fan tonal noise in cluttered environments.
Near-field scattering of ducted fan noise using a boundary element method
Authors: Schram Christophe
Published: May 2008

The noise emitted by rotating machinery is a concern in many applications, such as aeroengines, wind turbines, and cooling devices for IC engines or electronic appliances. A specific derivation of the Ffowcs Williams and Hawkings analogy for the tonal noise emitted by a fan was presented by Goldstein (1976), under the assumption that the listener is placed in the acoustical and geometrical far field. That formulation accounts for the modulation of the Doppler frequency shift during the fan revolution, but neglects near field effects. This work presents the application of an alternative derivation, introduced by Roger (2007), which preserves the near-field features of the sound field. This analytical method is compared with a second method in which the fan is modelled by a fixed azimuthal distribution of dipoles. A validation is performed for the case of a generic fan located in an infinite circular duct. The sound field within the duct is obtained by two means: i) calculating the sound field emitted by the fan, modelled by the above mentionned approaches, and scattered by the duct through the application of a Boundary Element Method, ii) computing the sound field by projecting the source in the duct modes.
Improvements of a parametric model for fan broadband and tonal noise
Authors: Moreau Antoine , Enghardt Lars
Published: May 2008

The fan of an aero-engine is one of the most significant noise sources of civil aircraft. The purpose of the present work is to provide a tool for fan noise prediction, which can be integrated into the design process of innovative fans. Fan noise is predicted by means of an analytic model. A single noise source is considered: the rotor-stator interaction noise due to rotor blade wakes impinging onto the stator vanes. This source is known to be the major source of fan broadband and tonal noise. The formula for the sound power is based on the single airfoil theory in far field developed by Amiet. It accounts for the effect of subsonic compressible flow and source non-compactness. The model accounts for fan parameters such as geometry (blade and vane count, chord length, rotor-stator gap) and flow parameters (mean velocities, wake and turbulence characteristics). Future work will investigate a more detailed description of the sound field based on an acoustic modal approach, in which each frequency component of the sound spectrum is decomposed into a distribution of duct acoustic modes.
Investigation into the effect of altering incoming gust shape to far field noise radiation in Amiet's theory
Authors: Bilka Michael , Anthoine Jerome
Published: May 2008

Noise prediction for turbulent interactions with fan-blades or high-lift devices has been continuously developed for the last thirty years. A benchmark solution to this problem is Amiet's theory for acoustic radiation from an airfoil in a turbulent stream. In most aerodynamic theories the incoming gust is assumed to be sinusoidal, which is also the case for the theory of Amiet. This assumption affects the derivation of the unsteady lift function which is used to propagate the noise to the far-field. This paper proposes to show the effect of altering the shape of the incoming gust by assuming a Gaussian function. This analysis will then be compared to the case of the sinusoidal gust as well as to acoustic measurements of an airfoil placed in a jet taken in the VKI semi-anechoic chamber.
Aeroacoustics of a low Mach number tip-gap flow
Authors: Grilliat Julien , Jacob Marc C.
Published: May 2008

A thorough experimental study was performed in several campaigns in the anechoic wind tunnel of the Ecole Centrale de Lyon on a single airfoil at a low Mach number to investigate the tip leakage flow and the associated broadband noise. The influence of the inflow velocity, the airfoil angle of attack and the gap size were characterized and hence an extensive data set was obtained. Both near field aerodynamic and far field acoustic features of this configuration were recorded. Statistical post-processing of the data highlighted some of the governing parameters of this jet-like flow configuration and two different noise generation mechanisms. Some scaling laws were derived from the experimental data which gave also inputs for semi-analytical far field noise prediction models relying on the theory for linearised unsteady aerodynamics around a slender airfoil. The underlying sound generation mechanism is the scattering of the tip clearance flow perturbations by the airfoil trailing edge. The aerodynamic perturbation is described as a gust with a spanwise distribution that is concentrated near the gap region. The models are presented and compared to experimental results and CFD calculations. This work has been funded by the European Community as part of the 6th Framework Project PROBAND n° AST4-CT-2005-012222.
Commercial thermoacoustic products and next-step developments in acoustic cooling
Authors: Corey John , Spoor Philip
Published: May 2008

CFIC-Qdrive committed to development and commercialization of thermoacoustic energy conversion devices in 1999, by combining the newly developed acoustic perspective and tools developed at Los Alamos with a deep well of Stirling-cycle experience to achieve a total physics model with both inertial and viscous behavior of the working fluid. Such acoustic-Stirling devices combine the mechanical simplicity, robustness, and efficiency. Focusing first on refrigeration for cryogenics; this work has led to a family of standard products that have found uses worldwide, from air-quality sampling and oil refinery support to military aviation oxygen liquefaction. This paper details the basic operation of these acoustic- Stirling products and the key technological elements that make them viable and attractive in cryogenics; then examines the implications for less-cold uses like food-storage and air-conditioning; with a discussion of achievable performance in accessible applications. We review the work now underway to develop devices to meet those opportunities with environmentally benign cooling of superior performance.
Generating electricity from burning wood using Thermo-acoustics for use in developing countries
Authors: Riley Paul H. , Johnson Mark
Published: May 2008

SCORE is a wood burning stove that will cook food, generate electricity and cooling for use in developing countries by means of thermoacoustics. The consortium of Nottingham (Lead), Manchester, Queen Mary, Imperial and City universities with the charity Practical Action, believe that the very demanding cost targets can be achieved by using thermo-acoustic technology due to the no-moving-part design. Standing wave and travelling wave designs are being evaluated with support from Los Alamos Laboratories in the US. The presentation will concentrate on the stove requirements and needs of the developing world and how this affects the thermo-acoustic and mechanical design. Results from mathematical modelling and measurements from an early demonstrator will be presented. More information can be found at Http://www.score.uk.com. The £2M Score research project is funded by EPSRC, a UK government agency.
Fundamental study of a loop-tube-type thermoacoustic cooling system using heat energy from condensed sunlight
Authors: Sakamoto Shin-Ichi , Komiya Shintaro , Miya Naoki , Senda Jiro , Watanabe Yoshiaki
Published: May 2008

The feasibility of implementation of a sunlight-based loop-tube-type thermoacoustic cooling system is investigated. Sunlight is condensed using a 0.60 m diameter Fresnel lens and irradiated to the high-temperature heat exchanger. Then, the temperature of heat exchanger is risen. This heat energy from condensed sunlight is applied to the driving hear energy of the loop-tube-type thermoacoustic cooling system. The total length of the loop tube is 3300 mm, and a gaseous mixture of He and Ar (50% / 50%) is used as the working fluid. A 50-mm-long ceramic honeycomb is used for the stack. The channel radius of the prime mover stack is 0.45 mm; that of the heat pump is 0.35 mm. The cooling point temperature falls from 29°C to -4.3°C before sunlight is irradiated to the high-temperature heat exchanger. Consequently, a temperature drop of 33.3°C is achieved using sunlight. Result obtained in this experiment underscores the feasibility of implementation of a sunlight-based loop-tube-type thermoacoustic cooling system.
Geometry effects and scaling in thermoacoustics
Authors: Zeegers Jos
Published: May 2008

Current work at TU Eindhoven on thermoacoustics will be discussed. The end effects of the geometry of a stack on the performance of thermoacoustic machines will be shown. End effects and the formation of vortices is an issue that contributes to enhanced convective losses at the stack ends. Influence of Reynolds and Strouhal numbers on the oscillatory flow field in the stack are studied. It is possible to plot Sr and Re number diagrams in which various zones can be identified that display characteristic flow patterns. Furthermore the influence of the type of regenerator material is studied in traveling wave engines. Performance of honeycomb material of high-density pores is compared with wire screen regenerators in a thermoacoustic motor. As a last point the effects of downscaling to miniature systems is discussed. Limits of how far the size of a thermoacoustic cooler can be downscaled before conduction effects limit the performance are relevant.
Suppression of harmonics in a high frequency standing-wave thermoacoustic engine
Authors: Dai Wei , Yu Bo , Yu Guoyao , Luo Ercang
Published: May 2008

A thermoacoustic engine converts heat into acoustic power and could be used to driven a cooler for refrigeration purposes or to drive a piston for electric power generation. Due to non-linear effects inside the system, higher order harmonics could be generated which may deteriorate the thermal performance of the whole system. In this report, a 500Hz standing wave thermoacoustic engine has been built. The occurrence of higher order acoustic oscillations has been closely observed. A series of experiments has been done to investigate the influence of resonance tube configuration on this phenomenon. The influence on the related thermal performance is also reported.
Scalability of Thermoacoustic Refrigerator
Authors: Abdel-Rahman Ehab
Published: May 2008

The uses of thermoacoustic effect are the conversion of heat onto acoustic wave by thermoacoustic prime mover and pumping heat by acoustic wave using a thermoacoustic refrigerator. Thermoacoustic refrigerator is a good alternative to conventional vapor compression device. It can be very compact, using a minimum of uncomplicated, economical components. It can also provide variable cooling capacity and scalability to different sizes in ways that conventional vapor compression technology is not capable of. We are investigating the minimum size of a thermoacoustic refrigerator that can meet the cooling requirement for different applications. The coefficient of performance (COP) of small thermoacoustic refrigerators is in the range of 20% of the ideal (Carnot cycle) COP, which is actually better than similarly scaled vapor compression coolers which is at about 10%. The efficiency of thermoacoustic refrigerator can be improved by better designing of its components. In this paper the effect of components design on the performance of thermoacoustic refrigerator is discussed. The scalability of such devices is also investigated.
Recent developments in miniaturization of thermoacoustic devices
Authors: Lotton Pierrick , Penelet Guillaume , Gaviot Etienne , Durand Stephane , Camberlein Lionel , Blanc-Benon Philippe , Bruneau Michel
Published: May 2008

This talk will present a review of recent works on thermoacoustic devices miniaturization conducted at Laboratoire d'Acoustique de l'Universite du Maine (LAUM), in collaboration with Laboratoire de Mecanique de Fluides et d'Acoustique (LMFA). A part of these works deals with new designs allowing higher compactness of devices. As an example, a compact non-resonant thermoacoustic refrigerator will be described, and experimental results obtained on a prototype will be presented. Another part of these works deals with the miniaturization of each element of a thermoacoustic device, especially the stack and the acoustic source. The acoustical and thermal sensors used to control these small devices have also to be miniaturized. Some specific actuators and sensors designed for miniaturized thermoacoustic refrigerators will be presented. Finally, potential applications of these miniaturized devices will be discussed.
Nonlinear effects in standing-wave types of thermoacoustic devices
Authors: Aben Paul , Zeegers Jos
Published: May 2008

In order to create high amplitudes (p'/p0>10%) for a relatively low frequency range (between 5 and 125 Hz), a large subwoofer is connected to a resonator tube by an exponential horn. A parallel-plate stack, with various plate thicknesses and separations, can be placed at different positions in the resonator tube. The position of the subwoofer membrane, the voltage and current of the subwoofer, as well as the pressure at six different positions in the resonator is measured. The measurements are in good agreement with simulations. Using a multi-microphone method the transfer matrix of a stack is determined experimentally. Using a PIV method a 2-D velocity field between and around the stack plates is measured. The vortex shedding at the end of stack plates is studied in particular. The amplitude, frequency, plate thickness, plate separation and plate-ending shape are varied. Also the streaming velocity field is studied. Small asymmetries in the geometry have a huge influence on the streaming velocity.
Design road-map for thermoacoustic refrigerators
Authors: Ghorbanian Kaveh , Hosseini Hemed , Jafargholi Mahmoud
Published: May 2008

The main purpose of this work is to develop a road-map to enhance the design procedure and performance analysis of thermoacoustic refrigerators (TAR). The basic mechanism of TAR is very simple and is based on the wave interaction processes of gas particles with their surrounding environment. As known, the performance of a TAR system is highly dependent to the number of gas particles involved in the process. The essential components of TAR include a sound generating device, a resonance tube, a stack of plates, and heat exchangers. In this paper, the parameters influencing the performance of a TAR system are grouped into four blocks: (I) Operation (drive ratio, operating frequency), (II) Fluid (Prandtl number), (III) Geometry (blockage ratio, tube diameter, stack length, stack positioning), and (IV) Material. A parametric study is executed to determine the optimized design of a TAR system for fixed Block II and IV scenario. First, an analysis is made on obtaining the optimum number of gas particles to be involved in the process. Then, based on this, an optimization approach is carried out to identify the best drive ratio, blockage ratio, stack positioning, stack length, and resonance tube diameter. Finally, results are compared with experimental data.
Thermoacoustics in random fibrous materials
Authors: Jensen Carl R. , Raspet Richard , Bass Henry E.
Published: May 2008

Current approaches to acoustics in fibrous and porous materials use fitting parameters to match theoretical models to measured values for the material's complex compressibility and wavenumber. In effect, these models treat the material as though it were composed of an array of rigid capillary tubes; they have proven accurate in fitting the model to data for various different porous materials such as wools and foams. However, these models do not address thermoacoustic heat transfer when the material is put under a static temperature gradient. A direct simulation has been performed using a three-dimensional thermal fluid solver to calculate both the acoustic properties and the thermoacoustic properties of a random fibrous material. The results of the simulation will be compared to experimental results for complex compressibility and wavenumber [Tarnow, H., J. Acoust. Soc. Am., 97(4),2272-81] as well as a proposed extension to porous theory that incorporates thermoacoustics [Roh et al., J. Acoust. Soc. Am., 121(3), 1413-22]. [Work supported by U.S. Army Space & Missile Defense Command.]
Numerical study of the performance of thermally isolated thermoacoustic-stacks in the linear regime
Authors: Piccolo Antonio , Pistone Giuseppe
Published: May 2008

A simplified calculus model to investigate on the transverse heat transport near the edges of a thermally isolated thermoacoustic stack in the low acoustic Mach number regime is presented. The proposed methodology relies on the well known results of the classical linear thermoacoustic theory which are implemented into an energy balance calculus-scheme through a finite difference technique. Details of the time-averaged temperature and heat flux density distributions along a pore cross-section of the stack are given. It is shown that a net heat exchange between the fluid and the solid walls takes place only near the edges of the stack plates, at distances from the ends not exceeding the peak-to-peak particle displacement amplitude. The structure of the mean temperature field within a stack plate is also investigated; this last results not uniform near its terminations giving rise to a smaller temperature difference between the plate extremities than that predicted by the standard linear theory. This result, when compared with experimental measurements available in literature, suggests that thermal effects localized at the stack edges may play an important role as sources of the deviations found between linear theory predictions and experiments at low and moderate Mach numbers.
van der Waal gaz and direct simulation for thermoacoustics
Authors: Fontaine Alain , Mojtabi Marie-Catherine , Mojtabi Abdelkader , Breton Jean-Louis , Gibiat Vincent
Published: May 2008

Thermoacoustic refrigerators work with high amplitube acoustic waves and lead to high thermal local gradient near the stack. In order to understand nonlinear thermoacoustic effects, an acoustic plane wave is propagated in a model with a specific geometry. It is a two-dimensional channel with adiabatic walls, including two conductive plates whose thickness is not regarded as null.The fluid is supposed to be a real gaz with thermodynamic properties described by a van der Waals law. A two-dimensional direct numerical model for compressible flow is used to investigate unsteady dynamic and energetic behaviours in the channel. This model relies on a finite volume formulation of the mass, momentum and energy equations for compressible flow. Thermal equilibrium between gaz and plates is assured by a Dirichlet boundary condition for the interface temperature and a thermal conduction equation in the plate. Adiabatic walls are described by a Neumann boundary condition for the temperature on the wall. The acoustic wave is generated at the input. Perfectly Matched Layer (PML) is used on input and output as a boundary condition to deal with wave reflections. Numerical investigation will be presented and compared with linear classical model.
Modeling and simulation of Taconis oscillations in a framework of the boundary-layer theory
Authors: Sugimoto Nobumasa , Shimizu Dai
Published: May 2008

This paper develops a simplified one-dimensional model to simulate numerically the onset of Taconis oscillation in a helium-filled, quarter-wavelength tube in cryogenics. Introducing a boundary layer on the tube wall, nonlinear fluid-dynamical equations are averaged over the cross-section of the acoustic main-flow region outside of the boundary layer. The boundary layer gives rise to memory effects, which are taken into account in the form of half-order derivatives. For a smooth temperature distribution of the tube wall, an initial and boundary-value problem of the equations derived is solved numerically for evolution of a small disturbance. The boundary condition at the open end neglects radiation and requires the excess pressure to vanish, while the condition at the closed end takes account of the boundary layer. When the ratio of the temperature at the closed end to the one at the open end exceeds a critical value, the initial helium column becomes unstable to grow in amplitude and stationary self-excited Taconis oscillations of finite amplitude emerge. It is shown that even the first-order boundary-layer theory can describe such an evolution of a small unstable disturbance into self-excited oscillations.