A CAA Based Approach to Tone Haystacking

Ewert, Roland; Kornow, Oliver; Delfs, Jan; Yin, Jianping; Röber, Thomas; Rose, Marco

doi:10.2514/6.2009-3217

Cited by 16 publications

(19 citation statements)

References 9 publications

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“…The two results are very similar, which tend to confirm Ewert et al hypothesis. As a consequence, the PIANO computations realized in section IV with a convected vortex will only account for the velocity fluctuations induced by the vortex in the unsteady base flow, as it is done by Ewert et al 12,13 when solving similar equations. ) without enforcing the vortex pressure and density fields (ρ t = p t = 0) and ( ) with the pressure and density fields decribed in Eq.…”

Section: Iiia Validation On a Reference Case By Colonius Et Almentioning

confidence: 99%

“…Apart from this, a very good agreement is found between the two methods and the reference results. The hypothesis of Ewert et al 12,13 that the pressure and density fields induced by the vortex have a very low influence on the scattering can be assessed for this case in performing calculations with and without taking these pressure and density fields into account. When they are discarded, only the uniform pressure and density fields remains (ρ = ρ ∞ and p = p ∞ ).…”

Section: Iiia Validation On a Reference Case By Colonius Et Almentioning

confidence: 99%

“…Ewert et al 12,13 suffered from growing numerical instabilities when trying to solve these equations, because of the terms of Eq. (2) involving mean flow gradients.…”

Section: Iia Description Of the Configuration Studiedmentioning

confidence: 99%

“…(12). In the far-field (far from any flow perturbation due to the vortex), the scattered pressure can be expressed using a multipole expansion with modes amplitudes A m deduced from the pressure field calculated over the arrayȓ.…”

Section: Iic1 Equations Solved For a Steady Vortexmentioning

confidence: 99%

“…This model is able to consider frozen or evolving turbulence, and the variations of the source/flow parameters show behaviors of the spectra agreeing with existing experimental results. Ewert et al 12,13 perfomed first attempts of numerical calculations for such configurations solving the linearized Euler equations (LEE) in the time domain with a finite difference solver and using the stochastic RPM method in order to synthesize and introduce the turbulence in the numerical domain. The method showed promising results in its ability to recover features of the spectral broadening and its evolution with several parameters of the source or the flow.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Iiia Validation On a Reference Case By Colonius Et Almentioning

confidence: 99%

Section: Iiia Validation On a Reference Case By Colonius Et Almentioning

confidence: 99%

“…Ewert et al 12,13 suffered from growing numerical instabilities when trying to solve these equations, because of the terms of Eq. (2) involving mean flow gradients.…”

Section: Iia Description Of the Configuration Studiedmentioning

confidence: 99%

Section: Iic1 Equations Solved For a Steady Vortexmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Numerical assessment of the scattering of acoustic waves by turbulent structures

Clair

Gabard

2015

21st AIAA/CEAS Aeroacoustics Conference

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Aeroacoustics of High Fidelity URANS Simulations of Distributed Electric Propellers

Wickersheim,

Keßler,

Krämer

2023

Notes on Numerical Fluid Mechanics and Multidisciplinary Design

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Spectral broadening of acoustic waves by convected vortices

Clair¹,

Gabard²

2018

J. Fluid Mech.

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The scattering of acoustic waves by a moving vortex is studied in two dimensions to bring further insight into the physical mechanisms responsible for the spectral broadening caused by a region of turbulence. When propagating through turbulence, a monochromatic sound wave will be scattered over a range of frequencies, resulting in typical spectra with broadband sidelobes on either side of the tone. This spectral broadening, also called ‘haystacking’, is of importance for noise radiation from jet exhausts and for acoustic measurements in open-jet wind tunnels. A semianalytical model is formulated for a plane wave scattered by a vortex, including the influence of the convection of the vortex. This allows us to perform a detailed parametric study of the properties and evolution of the scattered field. A time-domain numerical model for the linearised Euler equations is also used to consider more general sound fields, such as that radiated by a point source in a uniform flow. The spectral broadening stems from the combination of the spatial scattering of sound due to the refraction of waves propagating through the vortex, and two Doppler shifts induced by the motion of the vortex relative to the source and of the observer relative to the vortex. The fact that the spectrum exhibits sidebands is directly explained by the directivity of the scattered field which is composed of several beams radiating from the vortex. The evolution of the acoustic spectra with the parameters considered in this paper is compared with the trends observed in previous experimental work on acoustic scattering by a jet shear layer.

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A CAA Based Approach to Tone Haystacking

Cited by 16 publications

References 9 publications

Numerical assessment of the scattering of acoustic waves by turbulent structures

Numerical assessment of the scattering of acoustic waves by turbulent structures

Aeroacoustics of High Fidelity URANS Simulations of Distributed Electric Propellers

Spectral broadening of acoustic waves by convected vortices

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