Numerical simulation of acoustic scattering by a plane turbulent shear layer: Spectral broadening study

Bennaceur, Iannis; Mincu, Daniel-Ciprian; Mary, Ivan; Terracol, Marc; Larchevêque, Lionel; Dupont, Pierre

doi:10.1016/j.compfluid.2016.08.012

Cited by 17 publications

(8 citation statements)

References 35 publications

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“…occurs downstream of the point of spanwise domain confinement, where A = 10. [17,19]. As noted above, Cases RMD1 and RMD2 reach a local aspect ratio of ten at x/θ i = 332, 781 respectively, but the peak u r.m.s.…”

Section: Mean Flow Statisticsmentioning

confidence: 60%

“…For mixing layers with a white noise inflow fluctuation environment the local aspect ratio of the flow, defined as the ratio of spanwise domain extent to local momentum thickness, must be greater than ten throughout the computational domain in order to prevent artificial confinement by the spanwise domain [17]. Artificial confinement of the flow has an adverse effect on the computed flow statistics [18,19], and leads to an alteration of the coherent structure dynamics [17]. As described above, simulations of the mixing layer with a white noise disturbance environment leads to oblique spanwise vortices that undergo localised interactions.…”

Section: Introductionmentioning

confidence: 99%

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Spanwise domain effects on streamwise vortices in the plane turbulent mixing layer

McMullan

2018

European Journal of Mechanics - B/Fluids

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Large Eddy Simulation is used to assess the influence of the spanwise domain extent on the evolution of the spatially stationary streamwise structure that exists in the simulated plane turbulent mixing layer. The mixing layers originate from a physically-correlated inflow condition, which produces accurate mixing layer mean flow statistics. For all three spanwise domains considered a spatially stationary streamwise structure is present. The streamwise structure is artificially confined when its wavelength matches that of the spanwise domain extent, and a criterion for confinement is postulated. The confinement has no significant negative impact on either the computed flow statistics, or the growth of the large-scale spanwise structures. These results demonstrate that the streamwise structure rides passively on the large-scale spanwise vortex structure. A simulation lacking in a spanwise direction produces poor turbulence statistics, and is not a reliable representation of the real mixing layer flow.

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Section: Mean Flow Statisticsmentioning

confidence: 60%

Section: Introductionmentioning

confidence: 99%

Spanwise domain effects on streamwise vortices in the plane turbulent mixing layer

McMullan

2018

European Journal of Mechanics - B/Fluids

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“…Despite issues in the choice of parameters, the method showed promising results in its ability to recover features of the spectral broadening. Recently, a Large Eddy Simulation of the scattering by a mixing layer was carried out by Bennaceur et al (2016). The results were compared against available experimental data with similar non-dimensional scattering parameters and good agreement was found for the shape and position of the sidebands.…”

Section: Introductionmentioning

confidence: 97%

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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“…Subsequently Clair and Gabard [13] carried out a numerical investigation of spectral broadening for radiation from a monopole source scattered by a layer of turbulence convected by a uniform flow. Furthermore, Bennaceur et al [14] carried out the first study of spectral broadening using the Large Eddy Simulation (LES) method. They compared their numerical results against measurements from Candel, Guedel & Julienne [1] and similar measurements from wind tunnel tests by Kröber, Hellmond & Koop [15].…”

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confidence: 99%

Spectral Broadening of Tonal Sound Propagating Through an Axisymmetric Turbulent Shear Layer

McAlpine

Tester

2020

AIAA Journal

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In aeroacoustics, spectral broadening refers to the scattering of tonal sound fields by turbulent shear layers, whereby the interaction of the sound with turbulent flow results in power lost from the tone and distributed into a broadband field around the tone frequency. Fan and turbine tone spectral broadening is known colloquially as "haystacking". Recently a new analytical model has been derived to predict weak spectral broadening of a tone radiated through a circular jet. A key part of the modeling is the choice of the two-point turbulent velocity cross-correlation function which is used to provide a statistical description of the turbulence in the shear layer. A new cross-correlation function for an axisymmetric turbulent shear layer formed by a circular jet, based on the theory for homogeneous axisymmetric turbulence, has been developed. Validation results of weak-scattering calculated using this correlation function show better agreement with measurements when compared to the results calculated using a correlation function based on the theory for homogeneous isotropic turbulence.Doppler factor, incident field [Hz] D = Doppler factor, scattered field [Hz] e (1) , e (2) = unit vectors defining orthogonal coordinate system f = frequency, incident field [Hz] F = frequency, scattered field [Hz] . AIAA Senior member.k = axial wavenumber, incident field [radm −1 ] K = axial wavenumber, scattered field [radm −1 ] L = integral lengthscale [m] m = azimuthal order, incident field M = azimuthal order, scattered field p = pressure [Pa] r c = jet radius [m] r = separation vector [m] R = specific gas constant [Jkg −1 K −1 ] R i j = turbulent velocity two-point cross-correlation R i j = turbulent velocity two-point cross-correlation (without temporal decay) s = azimuthal separation r µ φ [m] t = time [s] T = temperature [K] T = integral timescale [s] u = velocity (u, v, w) [ms −1 ] U c = turbulence convection velocity [ms −1 ] U J = core jet flow velocity [ms −1 ] U (r) = mean velocity profile [ms −1 ] (x,r, φ) = polar coordinate system (x, y, z) = Cartesian coordinate system Greek variables β = non-dimensional constant used to define temporal decay function γ = adiabatic constant C p /C V γ m = radial wavenumber, incident field [radm −1 ] Γ M = radial wavenumber, scattered field [radm −1 ] δ = shear layer thickness [m] θ = polar angle, incident field [rad] Θ = polar angle, scattered field [rad] 2 λ = unit vector defining axis of symmetry µ = spatial separation distance [m] ρ = density [kgm −3 ] τ = temporal separation time [s] Φ i j = turbulent velocity cross-spectrum ω = angular frequency, incident field [rads −1 ] Ω = angular frequency, scattered field [rads −1 ] Subscripts d = denotes directivity of the incident field D = denotes directivity of the scattered field i, j = indices denoting x, r or φ m = denotes azimuthal order of the incident field M = denotes azimuthal order of the scattered field s = denotes sound (acoustic) quantity t = denotes turbulent quantity ∞ = denotes value at infinity Superscripts = denotes pe...

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Numerical simulation of acoustic scattering by a plane turbulent shear layer: Spectral broadening study

Cited by 17 publications

References 35 publications

Spanwise domain effects on streamwise vortices in the plane turbulent mixing layer

Spanwise domain effects on streamwise vortices in the plane turbulent mixing layer

Spectral broadening of acoustic waves by convected vortices

Spectral Broadening of Tonal Sound Propagating Through an Axisymmetric Turbulent Shear Layer

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