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Author: César Legendre
Publisher: Lulu.com
ISBN: 1326232851
Category : Science
Languages : en
Pages : 378
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Book Description
The effects of vortical mean flows on the propagation of acoustic waves are numerous, from simple convection effects to instabilities in the acoustic phenomena, including absorption, reflection and refraction effects. Therefore, the role of vorticity in acoustic propagation besides noise generation has been a subject of controversial discussions since the foundation of aeroacoustics. In this work, a theoretical study with subsequent industrial applications has been performed, concerning the derivation of a family of scalar operators for aeroacoustics based in total enthalpy terms and including mean vorticity effects in the propagation.
Author: César Legendre
Publisher: Lulu.com
ISBN: 1326232851
Category : Science
Languages : en
Pages : 378
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Book Description
The effects of vortical mean flows on the propagation of acoustic waves are numerous, from simple convection effects to instabilities in the acoustic phenomena, including absorption, reflection and refraction effects. Therefore, the role of vorticity in acoustic propagation besides noise generation has been a subject of controversial discussions since the foundation of aeroacoustics. In this work, a theoretical study with subsequent industrial applications has been performed, concerning the derivation of a family of scalar operators for aeroacoustics based in total enthalpy terms and including mean vorticity effects in the propagation.
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781720404453
Category :
Languages : en
Pages : 46
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Book Description
It is generally recognized that interaction of vortices with downstream blades is a major source of noise production. To analyze this problem numerically, a two-dimensional model of inviscid flow together with the method of matched asymptotic expansions is proposed. The method of matched asymptotic expansions is used to match the inner region of incompressible flow to the outer region of compressible flow. Because of incompressibility, relatively simple numerical methods are available to treat multiple vortices and multiple bodies of arbitrary shape. Disturbances from vortices and bodies propagate outward as sound waves. Due to their interactions, either constructive or destructive interference may result. When it is destructive, the combined sound intensity can be reduced, sometimes substantially. In addition, an analytical solution to sound generation by the cascade-vonex interaction is given.Kao, Hsiao C.Glenn Research CenterNUMERICAL ANALYSIS; AERODYNAMIC NOISE; TWO DIMENSIONAL MODELS; VORTICES; NOISE REDUCTION; COMPRESSIBLE FLOW; INCOMPRESSIBLE FLOW; SOUND WAVES
Author: Michael F. Hess
Publisher:
ISBN:
Category :
Languages : en
Pages : 65
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Book Description
Author: Herbert S. Ribner
Publisher:
ISBN:
Category :
Languages : en
Pages : 8
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Book Description
Author: w. r. johnson
Publisher:
ISBN:
Category :
Languages : en
Pages : 144
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Book Description
Author: M. S. Howe
Publisher: Cambridge University Press
ISBN: 9780521012232
Category : Mathematics
Languages : en
Pages : 236
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Book Description
Table of contents
Author: M. A. Hollingsworth
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Author: H. S. Ribner
Publisher:
ISBN:
Category : Noise
Languages : en
Pages : 11
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Book Description
Author: Y. Auregan
Publisher: Springer
ISBN: 3540458808
Category : Science
Languages : en
Pages : 302
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Book Description
The coupling between acoustic waves and fluid flow motion is basically nonlinear, with the result that flow and sound modify themselves reciprocally with respect to generation and propagation properties. As a result this problem is investigated by many different communities, such as applied mathematics, acoustics and fluid mechanics. This book is the result of an international school which was held to discuss the foundation of sound--flow interactions, to share expertise and methodologies, and to promote cross-fertilization between the different disciplines involved. It consists essentially of a set of pedagogical lectures and is meant to serve not only as a compact source of reference for the experienced researcher but also as an advanced textbook for postgraduate students, and nonspecialists wishing to familiarize themselves in depth, at a research level, with this fascinating subject.
Author: Tinghui Zheng
Publisher:
ISBN:
Category : Airframes
Languages : en
Pages : 0
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Book Description
This study was motivated by airframe noise in aircraft and blade-vortex interaction (BVI) noise in helicopters. In this thesis, the sound generated by vortical disturbances in a subsonic flow around solid surfaces, using different vortex velocity formulations, was investigated by numerically solving the linearized or non-linearized Euler equations. Analytical solutions for this general case are not available because the wavelength of the generated acoustic wave is comparable to the vortex size, which is at variance to the compact source assumption of the acoustic analogy. Numerical errors associated with the discretization and boundary conditions were kept small using a high-order scheme with accurate non-reflecting boundary conditions. Stagnation flow on a flat plate, flow around a stationary and rotating cylinder, and that about two cylinders were taken as prototypes of real-world flows with strong gradients of mean pressure and velocity. Single and periodic vortices were taken into consideration. In addition, the effect of vortex core size, the street distance, street frequency, and the Mach number of the mean flow on sound generation and propagation were examined. The sound wave strength was found to be proportional to the vortex strength. If the acoustic pressure is normalized by the vortex strength, then all the distinct acoustic pressure profiles will collapse into single curve. Sound generation by vortex interaction with a solid surface, as well as its propagation, were found to be totally different between the Taylor's and Vatistas's vortices. The vortex core size and vortex street distance have minor influences on the acoustic pressure profile for sound waves radiated by the Vatistas vortex. Nevertheless, the change of the core size or the distance between the vortex rows significantly affects the sound pressure profile and sound directivity radiated by a Taylor vortex. The effects of the non-linear terms on sound wave properties were also investigated. The non-linear influence was found to increase with the vortex strength. A lifting cylinder is shown not only to increase the sound wave amplitude, but also to shift its directivity. The developed methods and computer codes can be used in the future as platforms to more elaborate methods that will predict the noise generated by multi-element airfoils, and the undercarriage of an aircraft. This will help reduce the need of costly, time consuming, wind tunnel and field experiments.
