Sound source radiation in two-dimensional shear flow

Candel, Sébastien

doi:10.2514/3.8057

Cited by 9 publications

(2 citation statements)

References 17 publications

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“…3(a)), in an area defined by x < 0 and jyj 6 1:5b j , the acoustic field presents an axisymmetric interference pattern. As pointed out by Candel [31], the existence of such stationary waves is due to the interaction between the waves directly emitted by the source and those reflected upstream by the flow. This phenomenon is reduced when the latter is heated, as can be observed on the snapshot in Fig.…”

Section: Jet Flowmentioning

confidence: 94%

Array processing for the localisation of noise sources in hot flows

Rakotoarisoa

Marx

Prax

et al. 2019

Mechanical Systems and Signal Processing

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This paper investigates the problem of localizing a sound source in a heated flow using a microphone array. Applications are found in studies dealing with the identification of sound sources in hot turbulent jets, or with the sound radiation from installed turbofans. Two configurations have been investigated: a shear layer flow (wind-tunnel type) and a jet flow. In the present study acoustic data are generated using a simulation based on the Linearized Euler Equations. For heated flows, refraction by temperature gradients is superimposed with refraction by velocity gradients, and the objective of this study is to assess whether this effect is important and how it can be accounted for in different source localisation methods. For this purpose, a time-reversal-based imaging method has been compared with a beamforming-based method in which the time-delays are computed based on ray tracing. For the shear flow, the results show that for high subsonic Mach numbers and steep thermal gradients, the thermal stratification must be taken into account to ensure a satisfactory precision of localisation for both methods. However, including the gradients of velocity and temperature is less crucial for imaging sound sources in the jet flow. The results indicate also that the localisation error is lower with the beamforming and ray-tracing technique than with the time-reversal technique, the latter being more sensitive to the limited array aperture.

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Section: Jet Flowmentioning

confidence: 94%

Array processing for the localisation of noise sources in hot flows

Rakotoarisoa

Marx

Prax

et al. 2019

Mechanical Systems and Signal Processing

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“…For the case η 0 ̸ = 0 the mean shear layer slope is simply added to b 0 and b 1 . Modeling the shear layer geometry in this manner differs from, e.g., the approach of Candel 84 , who assumed the interfaces parallel to the flow direction. The numerical model is compared to the solution from Amiet who used a vortex sheet to model the velocity field.…”

Section: Self-similar Görtler Solutionmentioning

confidence: 99%

Sound propagation corrections in open jet wind tunnels

Biesheuvel

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Noise produced by aircraft, wind turbines or drones is an increasing societal challenge. In order to develop more silent technology new silent designs are tested in wind tunnels. The wind tunnel environment, however, is different from the real world. Therefore, corrections are made to properly predict the acoustics of the application in the real world. Acoustic corrections, specifically aimed to be used in acoustic imaging techniques, are the topic of this thesis. The work is split into two parts. The first part concerns efficient mean flow corrections. The second part presents a method to improve the resolution of acoustic images when the acoustic waves propagate through a turbulent medium. The thesis begins with a background on sound propagation, including common correction models used within acoustic imaging techniques. Furthermore, the fundamentals of acoustic imaging by means of the beamforming method are described.Localization of aeroacoustic sound sources in open jet wind tunnel experiments is often performed using acoustic imaging techniques. These techniques require the evaluation of the acoustic propagation time between the sound source and observer, which depends on the flow topology. Most conventional predictions use either a ray-tracer, coupled with a modeled continuous velocity field, or use ray diffraction and a discretization of the velocity field by means of vortex sheets. A novel method is proposed in which the continuous velocity field is discretized into blocks of constant velocity separated by velocity discontinuities, thus removing the requirement for the velocity to be parallel to the surface that separates the blocks. The acoustic ray is solved by minimization of the acoustic propagation time. The computational effort is low compared to ray-tracing methods, while maintaining an improvement in accuracy compared to methodologies using vortex sheets. An empirical continuous velocity field is derived that models a selfsimilar shear layer expanding asymmetrically from a rectangular nozzle. Subsequently, this velocity field is discretized to compute the acoustic rays. Experimental results with a loudspeaker source placed in the open jet of a large industrial wind tunnel showed a decrease in source localization uncertainty compared to techniques based on vortex sheets. This is attributed to the inclusion of the shear layer slanting.A similar method is applied to an open jet wind tunnel experiment in which sound sources on high-lift devices are localized using acoustic imaging techniques. The lift force deflects the wind tunnel jet and therefore affects the flow topology. A method is presented to evaluate the propagation time when the jet is deflected. The deflected flow is modeled using potential flow theory and used as input for a ray-tracer to obtain the propagation time. Although accurate, a ray-tracer significantly increases the computational effort of acoustic imaging. Therefore, approximate ray solutions are again computed using the principle of least propagation time, significantly lowerin...

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A Review of Numerical Methods in Acoustic Wave Propagation

Candel

1986

Recent Advances in Aeroacoustics

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Sound source radiation in two-dimensional shear flow

Cited by 9 publications

References 17 publications

Array processing for the localisation of noise sources in hot flows

Array processing for the localisation of noise sources in hot flows

Sound propagation corrections in open jet wind tunnels

A Review of Numerical Methods in Acoustic Wave Propagation

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