Acoustic analogies are applied mostly in numerical aeroacoustics to reduce aeroacoustic sound sources to simple emitter types. They are therefore often also referred to as aeroacoustic analogies.
In general, aeroacoustic analogies are derived from the compressible
Navier-Stokes equations(NSE). The compressible NSE are rearranged into various forms of the inhomogeneous acoustic wave equation. Within these equations, source terms describe the acoustic sources. They consist of pressure and speed fluctuation as well as stress tensorand force terms. Approximationsare introduced to make the source terms independent of the acoustic variables. In this way, linearized equations are derive which describe the propagation of the acoustic waves in a homogeneous, resting medium. The latter is excited by the acoustic source terms, which are determined from the turbulent fluctuations. Since the aeroacoustics are described by the equations of classical acoustics, the methods are called aeroacoustic analogies.
The Lighthill-Analogy considers a free flow, as for example with an engine jet. The nonstationary fluctuations of the stream are represented by a distribution of
quadrupolesources in the same volume.
The Curle-Analogy is a formal solution of the Lighthill Analogy, which takes hard surfaces into consideration.
The Ffowcs Williams-Hawkings-Analogy is valid for aeroacoustic sources in relative motion with respect to a hard surface, as is the case in many technical applications for example in the automotive industry or in air travel. The calculation involves
quadrupole, dipoleand monopoleterms.
* Blumrich, R.: "Berechnungsmethoden für die Aeroakustik von Fahrzeugen". Tagungsband der ATZ/MTZ-Konferenz Akustik 2006, Stuttgart, 17-18.5.2006..
* Lighthill, M. J.: "On sound generated aerodynamically. I. General theory". Proc. Roy. Soc. 211(A) S. 564-587, London, 1952.
* Lighthill, M. J.: "On sound generated aerodynamically. I. General theory". Proc. Roy. Soc. 222(A) S. 1-34, London, 1954.
* Ffowcs Williams, J. E. and Hawkings, D. L.: "Sound Generation by Turbulence and Surfaces in Arbitrary Motion". Philosophical Transactions of the Royal Society, Vol. A264, Nr. 1151, 1969, S. 321-342
* Curle, N.: "The Influence of solid boundaries upon aerodynamic sound". Proc. Roy. Soc. Lond., A23, 505-514. 1955
* [http://www.ias.et.tu-dresden.de/akustik/Publikationen/Stroemungsakustik/koe2004_3.pdf Contribution of the Technical University of Dresden to the modeling of flow sound sources with elementary emitters.]
* [http://www.ias.et.tu-dresden.de/akustik/Publikationen/Stroemungsakustik/koe2000-1.pdf Contribution of the Technical University of Dresden to the history of aeroacoustics.]
Wikimedia Foundation. 2010.
Look at other dictionaries:
Acoustic metric — In mathematical physics, a metric describes the arrangement of relative distances within a surface or volume, usually measured by signals passing through the region – essentially describing the intrinsic geometry of the region. An acoustic metric … Wikipedia
Acoustic impedance — The acoustic impedance Z (or sound impedance) is a frequency f dependent parameter and is very useful, for example, for describing the behaviour of musical wind instruments. Mathematically, it is the sound pressure p divided by the particle… … Wikipedia
acoustic ohm — any one of several units measuring sound resistance. These units got their name by analogy with electric resistance, which is measured in ohms. The sound resistance across a surface in a given medium is defined to be the pressure of the… … Dictionary of units of measurement
Acoustic reflex — The acoustic reflex (stapedius reflex, attenuation reflex, or auditory reflex) is an involuntary muscle contraction that occurs in the middle ear of mammals in response to high intensity sound stimuli.When presented with a high intensity sound… … Wikipedia
acoustic impedance — Acoustics. the total reaction of a medium to the transmission of sound through it, expressed as the ratio of sound pressure to particle velocity at a given point in the medium. * * * ▪ physics absorption of sound in a medium, equal to the… … Universalium
Computational Aeroacoustics — While the discipline of Aeroacoustics is definitely dated back to the first publication of Sir James Lighthill in the early 1950s, the origin of Computational Aeroacoustics can only very likely be dated back to the middle of the 1980s.… … Wikipedia
Quartz crystal microbalance — A quartz crystal microbalance (QCM) measures a mass per unit area by measuring the change in frequency of a quartz crystal resonator. The resonance is disturbed by the addition or removal of a small mass due to oxide growth/decay or film… … Wikipedia
Aeroacoustics — is a branch of acoustics that studies noise generation via either turbulent fluid motion or aerodynamic forces interacting with surfaces. Noise generation can also be associated with periodically varying flows. Although no complete scientific… … Wikipedia
List of numerical analysis topics — This is a list of numerical analysis topics, by Wikipedia page. Contents 1 General 2 Error 3 Elementary and special functions 4 Numerical linear algebra … Wikipedia
List of mathematics articles (A) — NOTOC A A Beautiful Mind A Beautiful Mind (book) A Beautiful Mind (film) A Brief History of Time (film) A Course of Pure Mathematics A curious identity involving binomial coefficients A derivation of the discrete Fourier transform A equivalence A … Wikipedia