Spectral and wavelet analysis of an aero-acoustic feedback loop in a transonic outflow valve based on Schlieren imaging

International audienceOn commercial aircrafts, the adequate pressure ratio between the cabin and the exterior is regulated with circular outflow valves. At an operating pressure ratio equivalent to 17000ft in altitude, a tonal noise is observed at 11kHz and higher harmonics. A feedback loop is believed to be responsible for this tonal noise and it is studied on an extruded two-dimensional mock-up representative of the outflow valves including the sealing steps. A spectral analysis is performed on the Schlieren images in terms of pixel intensity for each pixel independently. This accentuates the aliasing phenomena of the higher harmonics when studying the maximum power spectral density. In order to highlight different patterns in the flow, phase maps are computed with respect to a particular pixel at 11kHz and harmonics. Last, the feedback mechanism is visible between the sealing step and the valve with the application of a novel wavelet-based technique on the Schlieren images

Aeroacoustic investigation of a ducted tail rotor using the Lattice-Boltzmann Method

Abstract: The present study focuses on the aeroacoustics aspects of a ducted rotor that could be used in helicopter electrically driven tail rotor systems. These systems are axial, low-solidity rotor-stator assemblies operating in low subsonic and transitional regimes at approach. Lattice Boltzmann (LBM) simulations are performed using a variable resolution (VR) mesh strategy that yields a proper convergence after ? 0.35 seconds. The flow behavior, far-field acoustic predictions, and directivity measurements are obtained with the LBM simulations and compared with experiments and RANS simulations done to the same tail rotor system. LBM gives closer predictions to experimentally aerodynamic properties than the RANS simulations. In addition, the direct far-field noise computations show a good overall match with experimental data.Communication présentée lors du congrès international tenu conjointement par Canadian Society for Mechanical Engineering (CSME) et Computational Fluid Dynamics Society of Canada (CFD Canada), à l’Université de Sherbrooke (Québec), du 28 au 31 mai 2023

Étude physique d'un actionneur piézoélectrique multi-couches non-linéaire et applications à l'absorption active des vibrations déterministes sur 1 puis 6 degrés de liberté

L'environnement entourant un mécanisme de précision est la principale cause de son mauvais fonctionnement ou tout simplement de ses limitations dans la précision des résultats obtenus. Notre entrée dans l'ère des nanotechnologies nous pousse à concevoir des dispositifs aptent [i.e. aptes] à isoler ces mécanismes de leur environnement afin d'en améliorer le fonctionnement. Le sujet de cette thèse est l'étude, la caractérisation et la conception d'un dispositif d'isolation actif des vibrations utilisant la technologie piézoélectrique. Pour ce faire, l'utilisation d'une plateforme active à plusieurs degrés de liberté utilisant des actionneurs piézoélectriques multicouches propose une solution élégante au problème de l'isolation vibratoire. Chaque degré de liberté de la plateforme sera contrôlé par un actionneur multicouche, c'est pourquoi, une partie de cette thèse comprendra l'étude physique d'un actionneur piézoélectrique et la validation d'un modèle à l'aide d'un absorbeur de vibrations monoaxe. Bien que de nombreux modèles existent à ce sujet, le modèle numérique de l'actionneur proposé combine une loi de comportement macroscopique et l'utilisation d'un opérateur numérique discret. La loi de comportement macroscopique de la ferroélectricité de Tiersten choisie ici, est généralisée au cas tri-dimentionnel alors que l'opérateur numérique de Preisach modélisera l'hystérésis du [i.e. due] au phénomène de polarisation rémanente propre au [i.e. aux] matériaux ferroélectriques. Ces équations seront réduites aux cas d'un matériau piézoélectrique présentant une anisotropie transversale due à sa direction privilégie [i.e. privilégiée] de polarisation (équivalente à celles de Tiersen) et appliquées à l'étude d'une couche de l'actionneur en sollicitation de traction-compression. Le nouveau modèle mono-couche obtenu permet l'étude d'un actionneur complet composé d'un nombre fini de couches. Ce modèle présente l'avantage de conserver les couplages entre déplacements, efforts, et sollicitations électriques tout en introduisant les non-linéarités ferroélectriques. Le modèle de l'actionneur, après identification expérimentale est utilisé pour effectuer les simulations d'un absorbeur actif de vibration mono-axe. Une introduction à l'isolation vibratoire et au contrôle actif des vibration [i.e. vibrations] utilisant des algorithmes par anticipation multi-entrées/multi-sorties est présentée ensuite et le développement d'un algorithme de contrôle non-linéaire utilisant un modèle interne est étudié pour le cas mono-axe et dans le cadre de perturbations vibratoires déterministes. La suite du document propose l'application de cette [i.e. cet] algorithme au contrôle multi-axe utilisant une plateforme active à 6 degrés de libertés matérialisée [i.e. matérialisées] par une plateforme de Stewart dont chaque colonne active est un actionneur multicouche piézoélectrique équivalente à celle utilisée pour l'absorbeur mono-axe

Noise Source Localisation in a Low Speed Automotive Engine Cooling Module

The sound generated by rotating machines is a topic that is more and more considered. In fact, this noise is an environmental concern in many industrial fields. The rotating machine studied here is an automotive engine cooling fan system. The noise produced by these fans is a major contributor to the total radiated noise and in certain cases it dominates other sources like the engine or the tires. Usually, the fan is extracting the air through a heat exchanger where a coolant fluid is circulating through a network of tubing. The heat exchanger is usually located close to the fan on its suction side. This creates a turbulent flow and participates to the generation of broadband noise. As the module is located in the engine bay, the upstream flow is distorted which leads to a strong tonal noise contribution. The impact of those distortion on the blades or struts generates tonal noise. The article aims to evaluate the contribution of acoustic sources located on the rotor blades. The source localization for rotating machine should take into account the Doppler effect as the sources are rotating with the fan. Classical beamforming works but it leads to continuous annulus sources. Sitjsma et al. 1 propose to solve this problem by using a transfer function for a moving monopole source in uniform flow to reconstruct the signal in the time domain and develop an algorithm able to deal with rotating sources, Autord ROtating Source Identifier (ROSI). Using this method, the measurement of the sound pressure of rotating sources can be done using an array of microphones. The proper implementation of the method was verified using the benchmark from 2. In the present study, a 60-microphones logarithmic array was used and the reconstruction of sound pressure level was done in third octave bands. Measurements were done in different rotational velocity of the fan in the anechoic chamber of Sherbrooke's university (UdeS) without any other flow restriction than the heat exchanger itself. A measurement was done at full RPM with and without heat exchanger to compare if it is transparent acoustically. The Directivity measurements were conducted as well. Both method has been compared to the central microphone of the microphone array. The present paper is a part of a collaborative project between UdeS and Von Karman Institute (VKI). The major aim is to conduct an experimental investigation of the fan noise in two different facilities and to compare the results. 1 P, Sijtsma and S, Oerlemans and H, Holthusen. "Location of rotating sources by phased array measurements'', AIAA 2001-2167, 2001 2 Herold, G. "Microphone Array Benchmark b11: rotating points sources'', 201

Air-Water interface: a key place for revealing protein interactions.

International audienceFrom their amphiphilic nature, proteins in solution adsorb spontaneously at hydrophobic interfaces. Proteins are thus able to change their conformation, which modifies their surface properties. In the confined space near the interface, these modifications favor the formation of many interactions of weak energy (hydrophobic interactions, hydrogen bonds, Van der Waals interactions), and thus the creation, in the interface plane, of a network of intermolecular interactions. Adsorbed proteins can thus, in favorable conditions, constitute at the interface a continuous film with visco-elastic properties. These mechanical properties contribute to the stabilization of the interface created in multiphasic systems such as foams. Our work focuses on the behavior at the air-water interface and, if needed the foam properties, of some model globular proteins: ovalbumin, lysozyme, ovotransferrin, β-lactoglobulin… The aim of our work is to understand, using these models, how protein properties (structure, biochemistry, physico-chemistry), potentially adjusted by the physico-chemical environment, chemical changes or thermo-mechanical treatments, take part in the interfacial behavior, film characteristics and macroscopic proprieties of foams (overrun, stability, texture). Besides, in systems where several proteins with different properties (size, hydrophobicity, charge, conformation flexibility,…) coexist, we look to understand how the interactions between proteins enhance behaviors that cannot be considered as the sum of the single behaviors. The issue over time is to control technological parameters to improve texture properties in relation to foaming capacity

Altered retinoic acid signalling underpins dentition evolution

Small variations in signalling pathways have been linked to phenotypic diversity and speciation. In vertebrates, teeth represent a reservoir of adaptive morphological structures that are prone to evolutionary change. Cyprinid fish display an impressive diversity in tooth number, but the signals that generate such diversity are unknown. Here, we show that retinoic acid (RA) availability influences tooth number size in Cyprinids. Heterozygous adult zebrafish heterozygous for the cyp26b1 mutant that encodes an enzyme able to degrade RA possess an extra tooth in the ventral row. Expression analysis of pharyngeal mesenchyme markers such as dlx2a and lhx6 shows lateral, anterior and dorsal expansion of these markers in RA-treated embryos, whereas the expression of the dental epithelium markers dlx2b and dlx3b is unchanged. Our analysis suggests that changes in RA signalling play an important role in the diversification of teeth in Cyprinids. Our work illustrates that through subtle changes in the expression of rate-limiting enzymes, the RA pathway is an active player of tooth evolution in fish

Retinoic acid controls tooth morphology and number in cypriniformes

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Perfusional deficit and the dynamics of cerebral edemas in experimental traumatic brain injury using perfusion and diffusion-weighted magnetic resonance imaging.

International audienceThe aim of this work was to characterize edema dynamics, cerebral blood volume, and flow alterations in an experimental model of brain trauma using quantitative diffusion and perfusion magnetic resonance imaging (MRI). Associated with an influx of water in the intracellular space 1-5 h post-trauma as demonstrated by the 40% reduction in apparent diffusion coefficient, a 70-80% reduction in cerebral blood flow was measured within the lesioned region. Transient hypoperfusion (40-50%) was also observed in the non-traumatized contralateral hemisphere, although there was no evidence of edema formation. After the initial cytotoxic edema, a clear evolution toward extracellular water accumulation was observed, demonstrated by an increase in apparent diffusion coefficient