Radiation, refraction and scattering of acoustic waves in a free shear flow

Candel, Sébastien; Guedel, A.; Julienne, A.

doi:10.2514/6.1976-544

Cited by 34 publications

(41 citation statements)

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“…V. In region B, defined by the reflected characteristic C_ (1) and the shear layer, the direct and reflected waves interfere producing fringes. A transmitted wave is formed in region C between the characteristic C + (2) and the shear layer. Upstream of C+ (1) and C + (2) the field vanishes.…”

Section: Source Radiation In the Presence Of Supersonic Streamsmentioning

confidence: 99%

Direct Fourier Synthesis of Waves: Application to Acoustic Source Radiation

Candel

Crance

1981

AIAA Journal

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In numerous situations of current interest in aeroacoustics the sound field propagates in a nonhomogeneous medium. This is typically the case of jet noise radiation. A widely used model in that situation consists of a thin vortex sheet separating two uniformly moving fluids. This model may be treated as a layered medium, and acoustic source radiation may be analyzed by Fourier transform techniques. The inversion of the Fourier solution is however difficult and requires far-field approximations. This difficulty is here avoided by constructing the wave field by direct Fourier synthesis. This method was shown, in a previous work to be fast, reliable, and superior to the standard approximations. It is applied here to source radiation in the vicinity of a vortex sheet separating uniformly moving streams. Complete wave field maps are given for subsonic and supersonic flow combinations, providing new insights on jet noise radiation and refraction in open wind tunnels. Nomenclature c = sound speed C = characteristic lines G = line source field in free space J 0 = Bessel function of order zero //£ = Hankel function of order zero satisfying the radiation condition at infinity h = source-interface distance / = complex number, V -1 k = wave number L = spatial extension of the calculation domain M = Mach number N = number of points used in the discrete Fourier transform p = pressure p -Fourier transform of pressure U = mean-flow velocity x,z = Cartesian coordinates a = spatial frequency, argument of Fourier transform a j± = branch points of 7, (/ = 1,2) 7, = defined in text by Eq. (10) 6( ) = delta function dj = defined in text by Eq. (11) Ax = spatial sampling period Aa = elementary spatial frequency filter 77 = interfacial displacement 0 = polar angle measured with respect to the x axis X = wavelength co = angular frequency Subscripts *= reduced (dimensionless) quantity / = subscript used to distinguish variables pertaining to region 1 (z < 0) and region 2 (z > 0)

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Section: Source Radiation In the Presence Of Supersonic Streamsmentioning

confidence: 99%

Direct Fourier Synthesis of Waves: Application to Acoustic Source Radiation

Candel

Crance

1981

AIAA Journal

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“…In the same context, Goedecke et al 17 developed a semianalytical model based on the scattering by a single eddy, later coupled to a numerical computation in which a turbulent volume is successively split into cells of different sizes, each containing an eddy. The scattering of an acoustic radiation by a turbulent shear layer has been investigated experimentally by Candel et al 7,8 considering an harmonic source on the jet centerline. The results showed a specific shape of the acoustic spectra consisting in an attenuated peak at the source frequency surrounded by two sidebands (or haystacks).…”

Section: Introductionmentioning

confidence: 99%

Numerical assessment of the scattering of acoustic waves by turbulent structures

Clair

Gabard

2015

21st AIAA/CEAS Aeroacoustics Conference

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The scattering of harmonic sound waves by a single vortex is studied to provide some insight into the more complex problem of sound scattering by a turbulent layer. Two different methods are used to model the scattering by a steady vortex or by a vortex convected in a uniform mean flow. The first method is based on the linearized Euler equations in the frequency domain and is used to study the scattering by a steady vortex. The speed of this method allows to perform a study of the spatial scattering of a plane wave over a wide range of frequencies, where analytical models previously developed are restricted either to low or high frequencies. The second method uses a finite difference solver, also based on the linearized Euler equations but in the time domain. This method is used to study the scattering by a vortex convected in a uniform mean fow, where a spectral scattering occurs in addition to the spatial scattering. A parametric study is realized, focusing on four parameters including the source frequency and the convection velocity. The spectra deduced from this study show a pattern similar to the haystacking observed in existing studies of the scattering by a turbulent shear layer. Some of the trends deduced from the parametric study are also in agreement with these previous observations. Thus, the detailled study of the scattering by a single eddy is able to provide further understanding of the turbulence scattering.

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“…The different steps to obtain the cross-spectral matrices are not given in this section, but they are detailed in [25]. We would like to point out here that the correction of refraction and convection effects of the acoustic rays between the focus points on the aircraft model and the microphones of the array are taken into account in the model CSM [22,23]. In contrast, only the correction of convection effects are considered in the model CSM, when the data is measured in the closed test section.…”

Section: Resultsmentioning

confidence: 99%

“…It was positioned out of the flow at a distance of 2.4 m from the longitudinal axis of the aircraft model. Consequently, the correction of refraction and convection effects of the acoustic rays between the focus points on the aircraft model and the microphones of the array was taken into account [23,24] in the model CSM to obtain actual locations and levels of the acoustic sources.…”

Section: Experimental Set-up In Cepra 19 and Data Processingmentioning

confidence: 99%

Spectral Estimation Method with Additive Noise

Blacodon¹

2009

15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)

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Array processing represents an extremely important area in aero-acoustics, in particular in the development of methods to extract the useful characteristics of acoustic sources such as their locations and absolute levels, starting from the received sound field. Generally, the methods are based on a deconvolution operation to remove the undesirable effects of smearing produced by array response. This process should be carried out after the additive noise has been suitably attenuated and, ideally, the deconvolution operator should amplify the noise as little as possible. We show that when a reference of noise is known beforehand, and under certain assumptions, that it is possible both to remove the smearing effect produced by array response and to reduce the noise contamination of the results using a method called Spectral Estimation Method With Additive Noise. This method has been applied to computer and experimental simulations involving acoustic sources radiating in a noisy environment. The levels of the sources were found with a good accuracy and the background noise highly reduced, confirming the validity of the approach and the good performance of the proposed method. Nomenclature c = sound speed in the propagation medium f = frequency in Hertz s f = sampling frequency of the measurement signals in Hertz i , m G = mi jkR i , m R / e G mi = k = c / f 2π , acoustic wave number M = number of microphones in the array 0 P = 20 µPa mi R = the distance between the i th monopole source and the m th microphone q Ω = integrated power levels of the source area q)] f ( [ B Γ = cross spectral matrix resulting from the noise sources measurement )] f ( [ mod Γ = cross spectral matrix obtained with the model )] f ( [ mes Γ = cross spectral matrix resulting from the acoustic measurement )] f ( [ S Γ = cross spectral matrix obtained with the model

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Radiation, refraction and scattering of acoustic waves in a free shear flow

Cited by 34 publications

References 0 publications

Direct Fourier Synthesis of Waves: Application to Acoustic Source Radiation

Direct Fourier Synthesis of Waves: Application to Acoustic Source Radiation

Numerical assessment of the scattering of acoustic waves by turbulent structures

Spectral Estimation Method with Additive Noise

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