Academic literature on the topic 'Acoustic Hawking radiation'
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Journal articles on the topic "Acoustic Hawking radiation"
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Carusotto, Iacopo, and Roberto Balbinot. "Acoustic Hawking radiation." Nature Physics 12, no. 10 (August 15, 2016): 897–98. http://dx.doi.org/10.1038/nphys3872.
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Zhou, Shiwei, and Kui Xiao. "Hawking radiation of analogous acoustic black holes." Modern Physics Letters A 35, no. 28 (July 30, 2020): 2050236. http://dx.doi.org/10.1142/s0217732320502363.
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Propagation of sound waves in a flowing fluid can be viewed as a minimally coupled massless scalar field propagating in curved spacetime. The analogue Hawking radiation from a spherically symmetric acoustic black hole and a (2 + 1)-dimensional rotating acoustic black hole are investigated respectively in Damour–Ruffini’s method. The emission rate and Hawking temperature are obtained, which are related to acoustic black holes parameter.
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Balbinot, Roberto, and Alessandro Fabbri. "The Hawking Effect in the Particles–Partners Correlations." Physics 5, no. 4 (September 27, 2023): 968–82. http://dx.doi.org/10.3390/physics5040063.
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We analyze the correlations functions across the horizon in Hawking black hole radiation to reveal the correlations between Hawking particles and their partners. The effects of the underlying space–time on this are shown in various examples ranging from acoustic black holes to regular black holes.
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PARENTANI, RENAUD. "WHAT DID WE LEARN FROM STUDYING ACOUSTIC BLACK HOLES?" International Journal of Modern Physics A 17, no. 20 (August 10, 2002): 2721–25. http://dx.doi.org/10.1142/s0217751x02011679.
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The study of acoustic black holes has been undertaken to provide new insights about the role of high frequencies in black hole evaporation. Because of the infinite gravitational redshift from the event horizon, Hawking quanta emerge from configurations which possessed ultra high (trans-Planckian) frequencies. Therefore Hawking radiation cannot be derived within the framework of a low energy effective theory; and in all derivations there are some assumptions concerning Planck scale physics. The analogy with condensed matter physics was thus introduced to see if the asymptotic properties of the Hawking phonons emitted by an acoustic black hole, namely stationarity and thermality, are sensitive to the high frequency physics which stems from the granular character of matter and which is governed by a non-linear dispersion relation. In 1995 Unruh showed that they are not sensitive in this respect, in spite of the fact that phonon propagation near the (acoustic) horizon drastically differs from that of photons. In 2000 the same analogy was used to establish the robustness of the spectrum of primordial density fluctuations in inflationary models. This analogy is currently stimulating research for experimenting Hawking radiation. Finally it could also be a useful guide for going beyond the semi-classical description of black hole evaporation.
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Zhang, Li-Chun, Huai-Fan Li, and Ren Zhao. "Hawking radiation from a rotating acoustic black hole." Physics Letters B 698, no. 5 (April 2011): 438–42. http://dx.doi.org/10.1016/j.physletb.2011.03.034.
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Visser, Matt. "Acoustic black holes: horizons, ergospheres and Hawking radiation." Classical and Quantum Gravity 15, no. 6 (June 1, 1998): 1767–91. http://dx.doi.org/10.1088/0264-9381/15/6/024.
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Fagnocchi, Serena. "Correlations of Hawking radiation in acoustic black holes." Journal of Physics: Conference Series 222 (April 1, 2010): 012036. http://dx.doi.org/10.1088/1742-6596/222/1/012036.
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Kim, Wontae, and Hyeonjoon Shin. "Anomaly analysis of Hawking radiation from acoustic black hole." Journal of High Energy Physics 2007, no. 07 (July 27, 2007): 070. http://dx.doi.org/10.1088/1126-6708/2007/07/070.
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BÉCAR, RAMÓN, PABLO GONZÁLEZ, GUSTAVO PULGAR, and JOEL SAAVEDRA. "HAWKING RADIATION VIA ANOMALY AND TUNNELING METHOD BY UNRUH'S AND CANONICAL ACOUSTIC BLACK HOLE." International Journal of Modern Physics A 25, no. 07 (March 20, 2010): 1463–75. http://dx.doi.org/10.1142/s0217751x10048081.
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We study the Hawking radiation by Unruh's and canonical acoustic black hole from the viewpoint of anomaly cancelation method developed by Robinson and Wilczek and by the simple and physically intuitive picture given by the tunneling mechanism.
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Liberati, Stefano, Giovanni Tricella, and Andrea Trombettoni. "Back-Reaction in Canonical Analogue Black Holes." Applied Sciences 10, no. 24 (December 11, 2020): 8868. http://dx.doi.org/10.3390/app10248868.
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We study the back-reaction associated with Hawking evaporation of an acoustic canonical analogue black hole in a Bose–Einstein condensate. We show that the emission of Hawking radiation induces a local back-reaction on the condensate, perturbing it in the near-horizon region, and a global back-reaction in the density distribution of the atoms. We discuss how these results produce useful insights into the process of black hole evaporation and its compatibility with a unitary evolution.
Dissertations / Theses on the topic "Acoustic Hawking radiation"
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De, Vito Marco. "Analytic aspects of analogue Hawking radiation in Bose-Einstein condensates." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022. http://amslaurea.unibo.it/25570/.
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We present a theoretical study of analogue Hawking effect in stepwise models of Bose-Einstein condensates. We focus on subsonic-supersonic configuration, where two stationary homogeneous condensates are connected by a step-like discontinuity in the local speed of sound. We provide a detailed analysis of the scattering processes of fluctuation modes at the sonic horizon based on microscopic Bogoliubov theory of dilute BECs. Spontaneous phonon emission is predicted to occur at the
horizon as a conversion of vacuum fluctuations into on-shell real particles. The condensed-matter analogue of Hawking radiation arises as a thermal Bose spectrum to low frequency order in the subsonic region. Stepwise BEC configurations with an extended sonic region are also taken into account in order to address more
general and realistic velocity flow profiles.
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LUNA, Gabriela Coutinho. "Radiação Hawking de um buraco negro acústico não-comutativo." Universidade Federal de Campina Grande, 2016. http://dspace.sti.ufcg.edu.br:8080/jspui/handle/riufcg/2139.
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Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-11-06T20:40:37Z
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O estudo do buraco negro acústico, ou análogo acústico, se assemelha ao gravitacional da seguinte forma: verifi ca-se o fenômeno da radiação Hawking, apresença de um horizonte de eventos, a possibilidade de se calcular a sua temperatura, também chamada de temperatura Hawking, e obtêm-se uma métrica que descreve a geometria do buraco negro. Inserimos na métrica acústica a teoria não-comutativa, a fim de vericar as correções que resultam desta teoria. Neste trabalho, consideramos o princípio da incerteza generalizado, no formalismo de tunelamento via método de Hamilton-Jacobi, para determinar a temperatura Hawking e a entropia quântica corrigida para buracos negros acústicos não comutativo sem 2+1 dimensões. Em nossos resultados obtemos uma entropia de área, comum termo de correção logarítmica em ordem dominante um termo, em ordem menor, proporcional à temperatura de radiação associada com os buracos negros acústicos comutativos e um termo extra que depende de uma carga conservada. Assim, como no caso gravitacional, não há necessidade de apresentar o corte ultravioleta e as divergências são eliminadas.
Acoustic black hole study resembles the gravitational black hole as follows: we verify Hawking radiation phenomenon the presence of an event horizon, the possibility to calculate its temperature, also known as Hawking temperature, and we obtain a metric that describes the black hole geometry. We insert in the acoustic metric theory the non commutative theory in order to verify the corrections that result from this theory. In this study, we consider the generalized uncertainty principle in tunneling formalism by Hamilton-Jacobi method to determine Hawking temperature and quantum entropy corrected for non commutative acoustic black holes in 2+1 dimensions. In our results, we obtain an entropy are a with a termoflogarith mic correction in ruling order a termina smaller order, proportional to the radiation temperature associated with the commutative acoustic black holes and an extra term that depends on a conserved charge. Thus as in the gravitational case, there is noneed to present the ultraviolet cut-off and differences are eliminated.
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Ciliberto, Giorgio. "Non-locality and Back-reaction in Acoustic Black Holes and Non-linearity in Quantum Fluid Dynamics." Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASP174.
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Cette thèse porte essentiellement sur les corrélations quantiques et les fluctuations non-lineaires dans les fluides quantiques. Elle se concentre spéficiquement sur les fluctuations quantiques collectives, à savoir les ondes sonores, dans le flux stationnaire d'un quasi- condensat 1D de Bose-Einstein qui présente un horizon acoustique, c'est-à-dire une transition du flux d'un régime subsonique à un régime supersonique. Les phénomènes quantiques générés par la présence de l'horizon sont étudiés. La thèse présente également un bref excursus sur les turbulences dans un fluide quantique bidimensionnel.Nous étudions la non-séparabilité quantique, la non-localité et la rétro-action du rayonnement acoustique de Hawking émis par un trou noir analogue. L'intrication et les corrélations non locales au sein du système tri- partite de quasi-particules émises par l'horizon acoustique sont d'abord étudiées. Les équations de rétro-action qui régissent l'effet de ce rayonnement acoustique sur le fond inhomogène sont dérivées et des solutions stationnaires sont considérées. Enfin, une théorie phénoménologique basée sur des contraintes topologiques pour la création et l'annihilation de vortex est appliquée efficacement aux don- nées expérimentales, permettant ainsi de rendre compte des phases de croissance et de décroissance des turbulencesThis thesis is mainly about quantum correlations and non-linear fluctuations in quantum fluids. It focuses especially on collective quantum fluctuations, i.e. sound waves, in the stationary flow of a 1D Bose-Einstein quasi- condensate which exhibits an acoustic horizon, i.e. a transition from subsonic to supersonic flow. Quantum phenomena generated by the presence of the horizon are investigated. The thesis also presents a brief excursus on two- dimensional turbulence in a quantum fluid.We study quantum non-separability, non- locality and back-reaction of the acoustic Hawking radiation emitted by an analog black hole. The entanglement and nonlocal correlations within the tripartite system of quasi-particles emitted from the acoustic horizon are first investigated. Back-reaction equations govern- ing the effect of such acoustic radiation on the inhomogeneous background are derived and stationary solutions are considered. Finally, a phenomenological theory based on topological constraints for vortex creation and annihilation is effectively applied to experimental data, thus accounting for the growth and decay of turbulence
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Larré, Pierre-Élie. "Fluctuations quantiques et effets non-linéaires dans les condensats de Bose-Einstein : des ondes de choc dispersives au rayonnement de Hawking acoustique." Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00875349.
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Cette thèse est dédiée à l'étude de l'analogue du rayonnement de Hawking dans les condensats de Bose-Einstein. Le premier chapitre présente de nouvelles configurations d'intérêt expérimental permettant de réaliser l'équivalent acoustique d'un trou noir gravitationnel dans l'écoulement d'un condensat atomique unidimensionnel. Nous donnons dans chaque cas une description analytique du profil de l'écoulement, des fluctuations quantiques associées et du spectre du rayonnement de Hawking. L'analyse des corrélations à deux corps de la densité dans l'espace des positions et des impulsions met en évidence l'émergence de signaux révélant l'effet Hawking dans nos systèmes. En démontrant une règle de somme vérifiée par la matrice densité à deux corps connexe, on montre que les corrélations à longue portée de la densité doivent être associées aux modifications diagonales de la matrice densité à deux corps lorsque l'écoulement du condensat présente un horizon acoustique. Motivés par des études expérimentales récentes de profils d'onde générés dans des condensats de polaritons en microcavité semi-conductrice, nous analysons dans un second chapitre les caractéristiques superfluides et dissipatives de l'écoulement autour d'un obstacle localisé d'un condensat de polaritons unidimensionnel obtenu par pompage incohérent. Nous examinons la réponse du condensat dans la limite des faibles perturbations et au moyen de la théorie de Whitham dans le régime non-linéaire. On identifie un régime dépendant du temps séparant deux types d'écoulement stationnaire et dissipatif : un principalement visqueux à faible vitesse et un autre caractérisé par un rayonnement de Cherenkov d'ondes de densité à grande vitesse. Nous présentons enfin des effets de polarisation obtenus en incluant le spin des polaritons dans la description du condensat et montrons dans le troisième chapitre que des effets similaires en présence d'un horizon acoustique pourraient être utilisés pour démontrer expérimentalement le rayonnement de Hawking dans les condensats de polaritons.
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Dargaud, Jean-Baptiste. "Simulation numérique de l'onde de souffle et du bruit de jet au décollage d'un lanceur." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2013. http://tel.archives-ouvertes.fr/tel-00995841.
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À l'allumage d'un lanceur spatial équipé de moteurs à propergol solide (MPS), une onde de souffle (ODS), caractérisée par un pic de grande amplitude et une large dépression, est générée pendant le transitoire de montée en pression. Puis le jet supersonique chaud rayonne un bruit de jet (BDJ) intense riche en composantes hautes fréquences. Cette thèse a été consacrée à la mise au point de méthodologies de simulation de ces phénomènes à l'aide de la plateforme de calcul CEDRE, en se comparant à des mesures expérimentales réalisées sur un petit MPS. Les phénomènes sont reproduits à l'aide de simulations aux grandes échelles (SGE). Les choix numériques (maillages, schémas) sont effectués à partir de cas-tests de validation. La méthodologie retenue pour l'ODS repose sur une approche directe simulant la génération et le transport de l'onde jusqu'aux capteurs expérimentaux. Ce calcul, qui estime aussi le transfert radiatif du jet, permet l'interprétation physique des phénomènes générateurs de l'ODS (effet piston du jet se développant). La prise en compte de la post combustion dans les premiers instants se révèle être un facteur de premier ordre concernant l'amplitude de l'ODS et son interaction avec le jet. Une approche hybride est adoptée pour le BDJ, chaînant une SGE du champ proche à la résolution des équations de Ffowcs Williams & Hawkings (FWH). Le bon accord du champ aérodynamique avec les mesures de la littérature incite à appliquer cette méthode au calcul de l'ODS. Finalement, celle-ci met en évidence le caractère fortement non-linéaire de l'ODS qui ne peut donc être rayonnée par FWH, et une interaction modèrée avec le jet, plus conforme aux observations expérimentales.
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Babb, James Patrick. "The derivation and quasinormal mode spectrum of acoustic anti-de sitter black hole analogues." Thesis, 2013. http://hdl.handle.net/1828/4484.
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Dumb holes (also known as acoustic black holes) are fluid flows which include an "acoustic horizon:" a surface, analogous to a gravitational horizon, beyond which sound may pass but never classically return. Soundwaves in these flows will therefore experience "effective geometries" which are identical to black hole spacetimes up to a conformal factor. By adjusting the parameters of the fluid flow, it is possible to create an effective geometry which is conformal to the Anti-de Sitter black hole spacetime- a geometry which has recieved a great deal of attention in recent years due to its conjectured holographic duality to Conformal Field Theories. While we would not expect an acoustic analogue of the AdS-CFT correspondence to exist, this dumb hole provides a means, at least in principle, of experimentally testing the theoretical properties of the AdS spacetime. In particular, I have calculated the quasinormal mode spectrum of this acoustic geometry.Graduate
0986
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jpbabb@yahoo.ca
Conference papers on the topic "Acoustic Hawking radiation"
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Zhang, Xinwen, Changchun Liu, and Bing Lin. "Prediction of Engine Intake Noise with Discontinuous Least-Square Finite Element Method in Frequency Domain Acoustics." In GPPS Xi'an21. GPPS, 2022. http://dx.doi.org/10.33737/gpps21-tc-195.
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In the frame of efficient passive treatment, intake noise prediction needs improving. This paper presents a novel numerical method for predicting acoustic propagation from axisymmetric ducted fans of high bypass ratio turbofan engine. Non-uniform mean flow convection and acoustic liner treatment is included. The linearized Euler equations are solved in the frequency domain. The spatial discretization is conducted with the discontinuous least-square finite element method so that the resulting algebraic equation is Hermitian conjugate symmetric. Moreover, the high-order accuracy and hp refinement is obtained while memory shared parallel computing strategy is used for convergence acceleration. Based on the near field acoustics, the porous Ffowcs Williams-Hawkings equation is solved for far field sound pressure level. Benchmark problems including monopole radiation in uniform mean flow and acoustic propagation in sheared mean flow are used to validate the capability. Simulations of the JT15D static test intake noise are performed, where the far field angle of peak sound pressure level, about 60° agrees well with experimental data and numerical data available in the literature.
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Gruber, Mathieu, Timothée Lonfils, Chloé Dumont, Laurence Vion, Adrien Dubois, and Timothy Delteil Mc Williams. "On the Fast Prediction of Open Rotor Tonal Interaction Noise." In ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-42579.
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This paper discusses the noise prediction of Contra Rotating Open Rotors (CROR) in the context of a multi-disciplinary rotor design. Propeller noise is believed to be one of the dominant sources of noise on CROR engines in all flight conditions that require high thrust. It is therefore important to consider acoustics as early as possible in the design process. At Snecma, blade design is tackled as a multi-disciplinary approach that involves among others; mechanics, dynamics, aerodynamics, acoustics and engine integration constraints. In this context, accurate prediction methods based on unsteady Computational Fluid Dynamics (CFD) cannot be used to predict tonal noise radiation because of the prohibitive time required for convergence. This paper focuses on the prediction of far field tonal interaction noise using the fast prediction platform Sandra, which complies with the timescale of a rotor design project. Sandra is composed of an aerodynamic module and an acoustic module. As a first approximation, the aerodynamic module uses either a lifting-line method or a lifting-surface method to compute the pressure fluctuations on the blades. A map of the flow velocity, which contains the velocity gradients of the wake and of the tip vortex behind the front rotor, is extracted from a Reynolds Averaged Navier-Stokes (RANS) CFD simulation downstream of the front rotor. A quasi-stationary approach, which uses the space and time symmetry of the isolated rotors CFD, allows the flow field to be decomposed along the azimuthal angle. The pressure fluctuations on the rear blade are finally computed for each position. The acoustic propagation is then performed in the time domain using Farassat’s formulation 1A of the Ffowcs Williams and Hawkings equation. It is shown that the physics of the interaction between the front and the rear rotor is well captured. Direct comparisons with the far field noise computed from a uRANS solution, and with experimental data, show very good agreement of the position of the angles of maximum noise radiation for harmonics of order 2 or lower. It is also shown that the relative noise radiation between various rotor geometries is reasonably well captured, which is a requirement to provide a fast and relevant method for multi-disciplinary propeller blade design.
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Williams, Robert, Joana Rocha, Edgar Matida, and Fred Nitzsche. "Assessment of Surface-Based Aeroacoustic Noise From Blades of a Vertical-Axis Wind Turbine." In ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-38199.
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Surface-based sources of aerodynamically-generated noise for the 17-m troposkien shape vertical-axis wind turbine are predicted using Farassat’s Formulation 1A of the Ffowcs Williams-Hawkings equation. By discretizing the three-dimensional turbine blades over the height of the turbine into constant-radius sections, the blades were aerodynamically modeled in two-dimensions in the horizontal plane by an unsteady panel method to obtain results for surface pressures and velocities. The acoustic pressure generated by the blades throughout their rotations was determined by the combination of loading and thickness noise sources on the surface of the blade sections in the time-domain. The simulation results were compared to experimental results for the acoustic pressure power spectral density. The sound pressure level around the turbine was found to have a slight dipole radiation pattern, caused primarily by the loading acoustic pressure on the blades.
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Shao, Weidong, and Jun Li. "Analytical and Numerical Investigations on the Aeroacoustical Oscillation of Flow Past the Cavity." In ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-42551.
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Noise radiated by aeroacoustical oscillation of low Mach number flow past a two-dimensional cavity has been investigated analytically and numerically using electro-acoustical analogy and a hybrid scheme combining CFD with an implementation of the porous Ffowcs Williams-Hawkings equation. The noise generation mechanism is illustrated and the interaction between flow and cavity as well as key factors of resonant frequency is discussed. The 2D compressible unsteady Reynolds averaged Navier-Stokes equations (URANS) are solved to obtain near field acoustic source and unsteady characteristics of cavity flow. A buffer domain is exerted along all external boundaries to suppress boundary wave reflection. Computed tonal frequency and amplitude of pressure oscillations demonstrate good agreement with previous computational simulations and experiments. The influences of the length and shape of the neck and porous inserts on the noise radiated to the far field are also investigated. The 3D far field numerical results show that at a certain incoming flow velocity and shear layer thickness the frequency of the dominant oscillation increases with the length of the neck and the magnitude in the downstream far field is 8dB greater than that in the upstream far field. The increasing chamfer decreases the resonance frequency and changes the effective streamwise opening length resulting in significant differences in acoustic pressure fluctuation. The porous inserts on the floor of the cavity reduce the mass flow flux through the cavity neck and accordingly suppress the amplitude of dominant oscillation. The preliminary simulations reveal promising methods for sound radiation control.
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Tellier, G., D. Fedala, S. Kouidri, and R. Rey. "Numerical Study of Time Domain Approach Applied to the Prediction of Noise Radiation From Rotating Blades." In ASME 2007 International Mechanical Engineering Congress and Exposition. ASMEDC, 2007. http://dx.doi.org/10.1115/imece2007-43494.
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Aeroacoustic formulations in time domain are frequently used to model the aerodynamic sound of airfoils, the time data being more accessible. The formulation 1A developed by Farassat, integral solution of the Ffowcs Williams and Hawkings equation, holds great interest because of its adequacy for surfaces in arbitrary motion. The aim of this work is to study the numerical sensitivity of this model to specified parameters and the geometry used in the calculation. The numerical algorithms, spatial and time discretizations, and approximations used for far-field acoustic simulation are presented. A parametrical study of the relevant criteria is carried out based on the Isom’s and Tam’s test cases. A helicopter blade airfoil as defined by Farassat to investigate the Isom’s case is used in this work. According to Isom, the acoustic response of a dipole source with a constant aerodynamic load ρ0c02 is equal to the thickness noise contribution. In practice, this observation is subject to numerical errors that are not systematically well controlled. Variations of these errors depending on the time step, Mach number and the source-observer distance are studied. The analysis is then extended to the Tam’s test case. Tam test case has the advantage of providing an analytical solution for the first harmonic.
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Lyrintzis, Anastasios S. "Some Recent Advances in the Use of Kirchhoff’s Method in Computational Aeroacoustics." In ASME 1998 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/imece1998-0541.
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Abstract A review of recent advances in the use of Kirchhoff’s method in Computational AeroAcoustics (CAA) is given. Kirchhoff’s integral formulation allows the radiating sound to be evaluated based on quantities on an arbitrary control surface if the wave equation is assumed outside. Thus only surface integrals are needed for the calculation of the far-field sound, instead of the volume integrals required by the traditional acoustic analogy method (i.e. Lighthill, Ffowcs Williams-Hawkings equation). A numerical CFD method is used for the evaluation of the flow-field solution in the near field and thus on the control surface. However, diffusion and dispersion errors associated with wave propagation in the far-field are avoided. The surface integrals and the first derivatives needed can be easily evaluated from the near-field numerical aerodynamic data. The equivalence of Kirchhoff’s method and Acoustic Analogy methods was recently proven rigorously. Kirchhoff’s integral formulation was also extended to include nonlinear source regions as well as refraction effects outside the Kirchhoff control surface. The method has been applied to helicopter noise, jet noise, propeller noise, ducted fan noise, etc. A simple set of portable Kirchhoff/Acoustic Analogy subroutines can be developed to calculate the far-field noise from inputs supplied by any aerodynamic near/mid-field code.
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Kendall-Torry, Christofer, and Florian Danner. "Investigations on Direct and Hybrid Sound Predictions." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-57612.
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As a result of dissipative and dispersive properties of numerical methods the accuracy of direct noise prediction degrades with increasing distance from the source. Hybrid approaches are hence applied to predict the acoustic farfield, which rely on an integration of disturbance quantities extracted from the nearfield flow solutions. In order to elaborate the influence of the integration limits on sound prediction, different approaches of the Ffowcs Williams and Hawkings method are systematically applied to an advanced counter rotating propfan configuration within the present study. The solutions of various permeable and impermeable integration surfaces are analysed with respect to nearfield sound radiation and compared against direct sound predictions from the compressible Reynolds-averaged Navier-Stokes solutions which likewise serve as input for the extrapolation routine. Due to the flexibility of the routine, source terms and zones can be selectively excluded from the surface integration, allowing a systematic identification of the origin of dissimilar sound prediction. Subsequent farfield analyses are used to conclude on the propagation and persistency of differences identified in the nearfield predictions.
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Gennaretti, Massimo, Claudio Testa, Giovanni Bernardini, and Alessandro Anobile. "An Analytical–Numerical Aerodynamic Formulation for Efficient Aeroacoustics Analysis of Rotorcraft." In ASME 2012 Noise Control and Acoustics Division Conference at InterNoise 2012. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/ncad2012-1081.
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This paper presents an analytical-numerical aerodynamic/aeroacoustic formulation for the analysis of the tonal noise emitted by helicopter rotors and propellers. It is particularly suited for those configurations dominated by local high-frequency changes (both in time and space) of blades inflow velocity. The solution of the Ffowcs Williams-Hawkings equation for noise radiation prediction is combined with the frequency-domain Küssner-Schwarz formulation that yields the sectional, unsteady aerodynamic loads, starting from the knowledge of the downwash on the airfoil due to blade motion and inflow induced on it by any external source of perturbation. Here, the blade inflow is assumed to be evaluated through a 3D, unsteady, panel method formulation suited for the analysis of rotors operating in a complex aerodynamic environment. This aerodynamic/aeroacoustic model gives a computationally efficient solution procedure that may be conveniently applied in preliminary design/multidisciplinary optimization applications. The proposed approach is validated through comparison with the (accurate, but computationally expensive) acoustic field obtained through the blade pressure loads directly evaluated by the time-marching panel-method solver. The results are provided in terms of blade loads, noise signatures and sound pressure level contours.
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Chen, Jiandong, Beibei Sun, Jianrun Zhang, Fei Xue, and Xin Liu. "Experimental and Numerical Investigation of the Aerodynamic Noise Radiated From a Centrifugal Blower." In ASME 2015 Noise Control and Acoustics Division Conference at InterNoise 2015. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/ncad2015-5916.
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Centrifugal blowers are widely used as garden machines, however, the aerodynamic noise generated by these machines cause serious problems. Although many researches focus on the generation mechanism and prediction method of centrifugal fan noise, most of these researches analysis the simplified centrifugal fan models and ignore the diffraction and scattering effect. In this paper, both experimental and numerical methods are carried out to analysis and measure the aerodynamic noise of the centrifugal blower. In order to calculate the flow field, a CFD (Computational Fluid Dynamics) numerical model is established, and the LES (Large Eddy Simulation) model is used to solve the three-dimensional unsteady flow, while the FW-H (Ffows Williams-Hawkings) model is used to calculate the acoustic source. To consider the diffraction and scattering effect, a BEM method is used to predict the sound radiated from the blower. A parallel experiment is carried out to measure the aerodynamic noise in a semi-anechoic room, and the numerical result shows a good agreement with the experiment result. The effect of outlet and inlet ducts on the sound radiation of the centrifugal blower is also investigated in this paper.
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Cai, Jian-Cheng, Jie Pan, and Andrew Guzzomi. "A Numerical Study of the Unsteady Flow Field and Tonal Hydrodynamic Sound of a Centrifugal Pump." In ASME 2015 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/imece2015-53163.
Full textAbstract:
In this paper, the 3-D unsteady turbulent flow inside a centrifugal pump is investigated by computational fluid dynamics (CFD) in ANSYS CFX, using Detached Eddy Simulation (DES) as the turbulence approach. The pump has a single end-suction and a single volute discharge. The impeller is semi-open (unshrouded with baseplate) and has five backswept blades and pump-out back blades. The CFD model of the pump consists of the inlet, the impeller, and the volute. A sliding mesh technique has been applied to the interfaces in order to allow unsteady interactions between the rotating impeller and the stationary parts. These unsteady interactions generate pressure fluctuations over the volute casing and blade surfaces that are hydroacoustic dipoles according to Lighthill’s acoustic analogy theory. The pressure fluctuation spectra at the volute tongue show that pressure fluctuations are generated mainly by the discrete components related to the impeller rotation at low frequencies, especially the blade-passing frequency (BPF) component. This component is approximately 1% of the reference dynamic pressure 0.5ρν22 where ν2 is the circumferential velocity at the impeller outlet. The discrete components with frequency larger than 4 times BPF are no longer obvious in the spectra. Compared to the experimental results, the CFD simulation predicts much lower amplitudes for the broad band pressure fluctuations. This is reasonable, because DES combines a classical Reynolds averaged Navier Stokes (RANS) simulation with elements of Large Eddy Simulation (LES), and both RANS and LES use average methods which filter out the high frequency fluctuations. Nevertheless, CFD is capable of accurately predict the BPF component. The pressure fluctuations on the casing and blade surfaces are extracted and modelled as the stationary and rotary dipoles, respectively, according to the Ffowcs Williams and Hawkings (FW-H) equation of the acoustic analogy theory. After Fast Fourier Transform, the spectra of the pressure fluctuations are obtained, and are used to predict the tonal hydrodynamic sound radiation at BPF and its low order harmonics. The sound radiation of casing surface dipoles is calculated by extracting the tonal components, and performing a surface integration with the fundamental solution to Helmholtz equation as the kernel. A frequency domain formulation of the FW-H equation with the moving surface dipole is employed to predict the tonal blade noise. The results from these acoustical simulations show that the sound power generated by the casing surface dipole is three orders of magnitude higher than that of the blade surface dipole, and the main hydroacoustic sources are located at the volute tongue.