Localisation de source acoustique en soufflerie anéchoïque par deux techniques d’antennerie : formation de voies et retournement temporel numérique

Beamforming (BF) is a powerful technique to localise sound sources in a wind-tunnel, but theflow effects on the acoustic propagation should be taken into account. An experiment is carried outin an anechoic wind-tunnel in order to validate the BF treatment associated to flow corrections.The results show that the BF technique can estimate very accurately the position of the source. However, the experiments are limited by the low speed of the wind-tunnel. So, a numerical code solving the linearized Euler equations (EEL) is used to simulate different flow conditions. We show that the apparent position shifting of the source, due to the effects of the flow is roughly proportional to the product of the Mach number by the thickness of the uniform flow. Furthermore, we show that the corrections remain robust for a higher Mach number. Then we present a new method for localising a source in a wind-tunnel based on the time-reversal technique. We show that EEL are invariant under time-reversal in changing the direction of the flow velocity. The experimental signals obtained are time-reversed and the backpropagation is performed numerically. The results show that it is possible to localise the source position, without BF assumptions and without flow corrections. The ability of the method to localise an intermittent aeroacoustic source is highlighted.Le développement croissant des moyens de transport a engendré des nuisances sonores en zone urbaine et périurbaine. Pour pallier ce problème les industriels sont amenés à effectuer des études en vue de la réduction du bruit. La première étape de ce travail consiste à localiser les zones responsables de la production sonore. Le traitement d’antenne microphonique associé à la formation de voies (beamforming) est une méthode classique et robuste de localisation de sources sonores. Dans le cas de sources aéroacoustiques, cette technique d’imagerie peut être appliquée in situ, engendrant un coût important, ou en soufflerie anéchoïque. L’application de cette technique à des mesures en soufflerie permet ainsi de localiser des sources de bruits dans un écoulement, mais les effets de l’écoulement sur la propagation doivent être pris en compte pour une localisation optimale. Une expérience de localisation de source est mise en place dans la soufflerie anéchoïque Eole afin de valider le traitement par formation de voies associé aux corrections des effets de l’écoulement. Deux modèles correctifs distincts sont testés (modèle d’Amiet et modèle de Koop). Les résultats montrent que cette technique permet d’estimer très précisément la position de la source acoustique. De plus, nous montrons que les effets de l’écoulement sur la propagation sont bien indépendants de la longueur d’onde acoustique. Cependant, les moyens techniques limitent l’étude sur la localisation de source à de faibles vitesses, ainsi un code numérique résolvant les équations d’Euler linéarisées est utilisé afin de simuler des conditions d’écoulement plus diverses. Nous mettons en évidence que le décalage apparent de la position de la source, dû aux effets de convection et réfraction des ondes acoustiques, est approximativement proportionnel au produit du nombre de Mach par l’épaisseur d’écoulement uniforme. De plus, nous montrons que les deux corrections testées demeurent robustes même pour un nombre de Mach élevé. Dans une seconde partie nous présentons une méthode originale de localisation de source pour l’aéroacoustique s’appuyant sur une technique connue en acoustique, le retournement temporel. Contrairement à la formation de voies, cette méthode ne fait aucune hypothèse sur le rayonnement de la source et sur la distance source-antenne. Nous montrons que les équations d’Euler linéarisées autour d’un écoulement moyen sont invariantes par retournement temporel en changeant le sens de l’écoulement moyen. Puis une étude numérique des capacités d’un miroir à retournement temporel pour la localisation de source monopolaire ou dipolaire en soufflerie est réalisée. Finalement des expériences sont menées en soufflerie; les signaux obtenus sont retournés temporellement et la phase de rétropropagation est réalisée numériquement. Les résultats montrent qu’il est possible de localiser la position de la source sans les hypothèses liées à la formation de voies et sans correction des effets de l’écoulement. De plus, les capacités de la méthode à localiser une source aéroacoustique intermittente sont mises en évidence

Tonal noise of a controlled-diffusion airfoil at low angle of attack and Reynolds number

International audienceThe acoustic signature of a controlled-diffusion airfoil immersed in a flow is experimentally characterized. Acoustic measurements have been carried out in an anechoic open-jet-wind-tunnel for low Reynolds numbers (from 5 Â 10 4 to 4.3 Â 10 5) and several angles of attack. As with the NACA0012, the acoustic spectrum is dominated by discrete tones. These tonal behaviors are divided into three different regimes. The first one is characterized by a dominant primary tone which is steady over time, surrounded by secondary peaks. The second consists of two unsteady primary tones associated with secondary peaks and the third consists of a hump dominated by several small peaks. A wavelet study allows one to identify an amplitude modulation of the acoustic signal mainly for the unsteady tonal regime. This amplitude modulation is equal to the frequency interval between two successive tones. Finally, a bispectral analysis explains the presence of tones at higher frequencies

Application of acoustic imaging techniques on snowmobile pass-by noise

International audienceSnowmobile manufacturers invest important efforts to reduce the noise emission of their products. The noise sources of snow-mobiles are multiple and closely spaced, leading to difficult source separation in practice. In this study, source imaging results for snowmobile pass-by noise are discussed. The experiments involve a 193-microphone Underbrink array, with synchronization of acoustic with video data provided by a high-speed camera. Both conventional beamforming and Clean-SC deconvolution are implemented to provide noise source maps of the snowmobile. The results clearly reveal noise emission from the engine, exhaust, and track depending on the frequency range considered

Municipal noise regulations in Quebec

International audienceIn Canada, there are three levels of governance (federal, provincial and municipal). We focus here on regulations related to environmental noise at the municipal level in the province of Quebec. We report on the main findings of a systematic review of 114 municipal regulations. The review covered regulations from 74 cities in Quebec, selected based on five criteria: size, geographical region, economic activity, proximity to major transportation infrastructure, and presence of outdoor recreational events. All official and up-to-date legal documents related to environmental noise were considered, including noise ordinances, rules of peace and order, and environmental protection acts. A qualitative analysis of definitions across documents indicates that environmental noise can be conceived as an acoustic phenomenon, an environmental pollutant, a public health concern, or a quality of life indicator. Other elements refer to the context in which it is experienced, in terms of time of day, zoning, activities and communities affected, as well as the agents producing noise. Furthermore, 35 municipalities include exposure limits in dBA mostly for overall sound level and 16 of them describe the measurement protocol. Most regulations rely on the energetic indicator LAeq,T, sometimes with corrections considering noise characteristics and emergence from the background noise. Despite variations across cities, limits typically center around: - 65 dBA outdoors and 45 dBA indoors for daytime, - 50 dBA outdoors and 40 dBA indoors for nighttime. The findings are discussed in light of best practices at the international level, including the World Health Organization guidelines. This research is funded by the Quebec ministries of Health (MSSS) and Environment (MELCC)

Comparison of Road Noise Policies across Australia, Europe, and North America

Developing innovative noise policies that build on international best practices is difficult when policies around the world differ along many dimensions, ranging from different sources covered to different levels of governance involved. This is particularly critical in the context of road traffic, identified as one of the main culprits leading to noise-associated complaints and health issues. In this article, we document the wide range of specifications observed in road traffic policies and propose a methodology to compare noise limits across noise policies. First, we present the responsibilities of administrative governments according to the scope (e.g., emission vs. exposure). Second, we compare noise limits by scope and geographic areas by separating acoustic indicators (overall and event indicators). Third, we convert overall outdoor noise limits into a common basis using the method described by Brink and his associates (2018) and compare them with the World Health Organization (WHO)’s recommendations (2018). Finally, measurement protocols are also compared across outdoor noise policies. This paper shows that road noise is managed at several administrative levels using approaches that are either centralized or decentralized. We also observed disparities in the associated noise limits across geographic areas. The converted outdoor noise limits generally exceeded the WHO’s recommendations (2018). Finally, this paper outlines how outdoor measurement protocols vary across geographic areas. However, similarities were identified between state and provincial noise policies within the same country