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Trailing Edge Noise Reduction by Passive and Active Flow Controls

This paper presents the results on the use of porous metal foams (passive control) and dielectric barrier surface plasma actuations (active control) for the reduction of vortex shedding tonal noises from the nonflat plate type trailing edge serration in a NACA0012 airfoil previously discussed in Chong et al. (AIAA J. Vol. 51, 2013, pp. 2665-2677). The use of porous metal foams to fill the interstices between adjacent members of the sawtooth can almost completely suppress the vortex shedding tonal noise, whilst the serration effect on the broadband noise reduction is retained. This concept will promote the nonflat plate type serrated trailing edge to become a genuine alternative to the conventional flat plate type serrated trailing edge, which is known to have drawbacks in the structural stability, aerodynamic performances and implementation issues. For the plasma actuators, configuration which produces electric wind in a tangential direction is found to be not very effective in suppressing the vortices emanated from the serration blunt root. On the other hand, for the plasma configuration which produces electric wind in a vertical direction, good level of vortex shedding tonal noise reduction has been demonstrated. However, the self noise produced by the plasma actuators negates the noise benefits on the tonal noise reduction. This characteristic illustrates the need to further develop the plasma actuators in a two pronged approach. First is to increase the electric wind speed, thereby allowing the plasma actuators to be used in a higher free jet velocity which naturally produces a larger level of jet noise. Second, the self noise radiated by the plasma actuators should be reduced

BinPo: An open-source code to compute the band structure of two-dimensional electron systems

We introduce BinPo, an open-source Python code to compute electronic properties of two-dimensional electron systems. A bulk tight binding Hamiltonian is constructed from relativistic density functional theory calculations represented in the basis of maximally localized Wannier functions. BinPo has a Schrödinger-Poisson solver, integrating an electric field-dependent relative permittivity to obtain self-consistently the confining electrostatic potential energy term in the derived tight binding slab system. The band structure, energy slices, and other properties, along with different projections and orientations can be computed. High resolution and publishable figures of the simulations can be generated. In BinPo, priority has been given to ease-of-use, efficiency, readability and modularity, therefore becoming suitable to produce reliable electronic structures simulations at low computational cost. Along with the code itself, we provide files from first-principles calculations for some materials, instructions of use, and detailed examples of its wide range of capabilities. The code was developed with a focus on the ABO3 perovskite structure-based systems, such as SrTiO3 and KTaO3, because of their increasing impact in the materials community. Some features, such as the projection onto orbital states, are restricted to calculations using the relevant orbitals for this family of materials, yet it is possible to include more elements in the basis for the band structure determination of other systems. The use of a relativistic approach allows for the inspection of the role of spin-orbit coupling and the resulting Rashba effect on the systems. We detail the approaches used in the code, so that it can be further exploited and adapted to other problems, such as adding new materials and functionalities which can strength the initial code scopes

Estimation indirecte de paramètres physiques d'un banc d'essai aéroacoustique en conduit

International audienceLa caractérisation des mécanismes de génération de bruit des machines tournantes est une problématique industrielle forte. Cette problématique est actuellement abordée par différentes approches complémentaires, à savoir des modèles analytiques, des simulations numériques ou des approches expérimentales. En ce qui concerne la partie expérimentale, différentes méthodologies basées sur la mesure du champ acoustique avec des antennes microphoniques ont été développées. De façon synthétique, le but est d’utiliser l’information du champ acoustique rayonné par la machine pour aller identifier des paramètres liés à l’origine du bruit, on parle donc d’un problème inverse. Un exemple d’application est la caractérisation du bruit rayonné par des machines tournantes carénées en utilisant des capteurs installés en paroi de conduit. Le caractère confiné du champ acoustique peut dans ce cas être exploité en réalisant une décomposition des mesures sur les modes de conduit. Cette décomposition est faite sur une base analytique dépendante de paramètres physiques tels quels la célérité acoustique, la vitesse moyenne de l’écoulement et le rayon interne du conduit. La connaissance exacte de ces paramètres est intéressante afin de réduire au maximum les erreurs de modèle, qui ont un impact important lorsqu’on parle de la résolution d’un problème inverse. L’objectif de cette contribution est de proposer un cadre pour une estimation raffinée des paramètres à partir seulement de mesures acoustiques par une antenne de microphones. Un critère pour l’estimation conjointe des paramètres est défini et évalué à partir de mesures sur un banc d’essai de ventilateur à différentes vitesses de rotation

Indirect calibration of a large microphone array for in-duct acoustic measurements

International audienceAbstract This paper addresses the problem of in situ calibration of a pin hole-mounted microphone array for in-duct acoustic measurements. One approach is to individually measure the frequency response of each microphone, by submitting the probe to be calibrated and a reference microphone to the same pressure field. Although simple, this task may be very time consuming for large microphone arrays and eventually suffer from lack of access to microphones once they are installed on the test bench. An alternative global calibration procedure is thus proposed in this paper. The approach is based on the fact that the acoustic pressure can be expanded onto an analytically known spatial basis. A projection operator is defined allowing the projection of measurements onto the duct modal basis. The main assumption of the method is that the residual resulting from the difference between actual and projected measurements is mainly dominated by calibration errors. An iterative procedure to estimate the calibration factors of each microphone is proposed and validated through an experimental set-up. In addition, it is shown that the proposed scheme allows an optimization of physical parameters such as the sound speed and parameters associated to the test bench itself, such as the duct radius or the termination reflection coefficient