Measurements of the distribution of sound source intensities in turbulent jets

Grosche, F.-R.; Jones, Jonathan E.; Wilhold, G. A.

doi:10.2514/6.1973-989

Cited by 13 publications

(13 citation statements)

References 11 publications

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“…Thus, the physical extents of gridz60A, gridz40A, gridz40B and gridz25B are respectively equal to Lz=60r0, 40r0, 40r0 and 25r0 in the axial direction, and to Lr=20r0, 15r0, 15r0 and 9r0 in the radial direction. According to experimental results, 31–37 the jet noise sources are expected to be fully captured on the first three grids, but it might not be the case for low-frequency sources typically below StD=0.2 on gridz25B, due to the limited extent in the axial direction in this case. For all grids, the number of points nθ in the azimuthal direction can be set to 256, 512 or 1024.…”

Section: Grid Parametersmentioning

confidence: 93%

“…Hence, the solutions obtained using the fifth grid of 251 million points were shown to be nearly converged with respect to the grid in the shear layers up to z=4r0 in the downstream direction, but no solid evidence of their accuracy further downstream was given. This is a pity because in subsonic jets, according to experiments, 31–37 high-frequency sound sources are located near the nozzle exit, whereas low-frequency sources lie farther downstream. In cold jets, 36 for instance, peak source locations are noted around z=6r0 for Strouhal number St D=fD/uj=2, where f is the frequency, but around z=12r0 for St D=0.5, and z=22r0 for StD=0.15, that is approximately the peak Strouhal number in the spectra measured in the jet direction.…”

Section: Introductionmentioning

confidence: 99%

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Grid sensitivity of flow field and noise of high-Reynolds-number jets computed by large-eddy simulation

Bogey

2018

International Journal of Aeroacoustics

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Three isothermal round jets at a Mach number of 0.9 and a diameter-based Reynolds number of 10 5 are computed by large-eddy simulation using four different meshes in order to investigate the grid sensitivity of the jet flow field and noise. The jets correspond to two initially fully laminar jets and one initially strongly disturbed jet considered in previous numerical studies. At the exit of a pipe nozzle of radius r 0 , they exhibit laminar boundary-layer mean-velocity profiles of thickness 0:2r 0 ; 0:025r 0 and 0:15r 0 , respectively. For the third jet, a peak turbulence intensity close to 9% is also imposed by forcing the boundary layer in the nozzle. The grids contain up to one billion points, and, compared to the grids used in previous simulations, they are finer in the axial direction downstream of the nozzle and in the radial direction on the jet axis and in the outer region of the mixing layers. The main flow field and noise characteristics given by the simulations, including the mixing-layer thickness, the centerline mean velocity, the turbulence intensities on the nozzle lip line and the jet axis, spectra of velocity and far-field pressure obtained from the jet near field by solving the isentropic linearized Euler equations, are presented. With respect to those from previous studies, the results are very similar for the initially laminar jet with thick boundary layers, but they differ significantly for the initially laminar jet with thin boundary layers and for the initially disturbed jet. For the latter two jets, using a finer grid leads to a faster flow development, to higher turbulence intensities in the shear layers and at the end of the potential core, to stronger large-scale structures, and to the generation of more low-frequency noise.

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Section: Grid Parametersmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Grid sensitivity of flow field and noise of high-Reynolds-number jets computed by large-eddy simulation

Bogey

2018

International Journal of Aeroacoustics

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“…So again the agreement may be partly fortuitous. But here also the parameter estimate has some rationale: the Davies et al value is an average along the jet from y / D = 1.5 to 4.5, but a better average would cover the major noise generating region, measured with an acoustic mirror technique as y / D = 4 to about 8 by Grosche, Jones & Wilhold (1973). This average should come to substantially less than 65 YO of the jet Mach number, since the jet centreline speed is down to about 82 Yo of the nozzle velocity at v / D = 8.…”

Section: Issue Of Convective Amplijicationmentioning

confidence: 99%

Effects of jet flow on jet noise via an extension to the Lighthill model

Ribner

1996

J. Fluid Mech.

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The Lighthill formalism for jet noise prediction is extended to accommodate wave transport by the mean jet flow. The extended theory combines the simplicity of the Lighthill approach with the generality of the more complex Lilley approach. There is full allowance for ‘flow-acoustic’ effects: shielding, as well as the refractive ‘cone of (relative) silence’. A source term expansion yielda a convected wave equation that retains the basic Lighthill source term. This leads to a general formula for power spectral density emitted from unit volume as the Lighthill-based value multiplied by a squared ‘normalized’ Green's function. The Green's function, referred to a stationary point source, delineates the refraction dominated ‘cone of silence’. The convective motion of the sources, with its powerful amplifying effect, also directional, is accounted for in the Lighthill factor. Source convection and wave convection are thereby decoupled, in contrast with the Lilley approach: this makes the physics more transparent. Moreover, the normalized Green's function appears to be near unity outside the ‘cone of silence’. This greatly reduces the labour of calculation: the relatively simple Lighthill-based prediction may be used beyond the cone, with extension inside via the Green's function. The function is obtained either experimentally (injected ‘point’ source) or numerically (computational aeroacoustics). Approximation by unity seems adequate except near the cone and except when there are coaxial or shrouding jets: in that case the difference from unity will quantify the shielding effect. Further extension yields dipole and monopole source terms (cf. Morfey, Mani, and others) when the mean flow possesses density gradients (e.g. hot jets).

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“…The experimental investigation of aeroacoustic sound sources began in the 1970-s. Back then, the standard measurement device was an elliptic mirror [21]. However, the application of microphone arrays soon found its way into the field.…”

Section: Introductionmentioning

confidence: 99%

Uniqueness of an inverse source problem in experimental aeroacoustics

2020

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This paper is concerned with the mathematical analysis of experimental methods for the estimation of the power of an uncorrelated, extended aeroacoustic source from measurements of correlations of pressure fluctuations. We formulate a continuous, infinite dimensional model describing these experimental techniques based on the convected Helmholtz equation in R 3 or R 2 . As a main result we prove that an unknown, compactly supported source power function is uniquely determined by idealized, noise-free correlation measurements. Our framework further allows for a precise characterization of state-of-the-art source reconstruction methods and their interrelations.

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Measurements of the distribution of sound source intensities in turbulent jets

Cited by 13 publications

References 11 publications

Grid sensitivity of flow field and noise of high-Reynolds-number jets computed by large-eddy simulation

Grid sensitivity of flow field and noise of high-Reynolds-number jets computed by large-eddy simulation

Effects of jet flow on jet noise via an extension to the Lighthill model

Uniqueness of an inverse source problem in experimental aeroacoustics

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