The acoustic field of a point source in a uniform boundary layer over an impedance plane

Zorumski, W. E.; Willshire, William L.

doi:10.2514/6.1986-1923

Cited by 2 publications

(3 citation statements)

References 2 publications

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“…11 An extensive experimental study of propagation of wind turbine noise at the 10-Hz one-third octave band out to 20 km has also been carried out together with a theoretical analysis. 12,13 However, as far as we know, there have not yet been published any results of comparison of experiments and FFP predictions of propagation of impulse, infrasound frequencies at the ranges studied here ͑out to 1400 m͒. To give reliable predictions of propagation of sound in the frequency range studied here is of practical interest, since atmospheric absorption is weak, about 0.1 to 0.5 dB/km.…”

Section: Introductionmentioning

confidence: 88%

Effects of strong sound velocity gradients on propagation of low-frequency impulse sound: Comparison of fast field program predictions and experimental data

Hole

Lunde

Gjessing³

1997

The Journal of the Acoustical Society of America

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As part of a large outdoor sound propagation experiment series, propagation of low-frequency impluse sound at ranges from 100 to 1400 m was studied at Haslemoen, Norway in February 1995. Sound sources were charges of 1 and 8 kg C4 explosives. Experiments were carried out in both a uniform forest and above a flat and uniform open field. Extensive meteorological measurements were carried out. Both automatic weather stations mounted in permanent towers and a tethered balloon were employed. The measurements resulted in a manifold set of sound velocity profiles. Occasionally, profiles were pure downwind or upwind, but mostly they were complex, often with large vertical gradients. One conclusion is that one should not uncritically use simple profile parameterizations, e.g., logarithmic, in sound propagation models. A fast field program (FFP), CAPROS, handles the complex sound-speed profiles well, predicting propagation of sound at 8, 16, 32.5, and 63 Hz. In this model, ground is considered a viscoelastic medium. At 63 Hz, the forest seems to cause an excess attenuation. At the lower frequencies, distinct effects of forest are not observed. There is no evidence that FFP predictions are less accurate in periods with high turbulence levels, which is here characterized with dynamical instability. However, variability of meteorological profiles causes predictions to be less accurate. This investigation suggests that it is sufficient to sample atmospheric variables up to 300 m above ground to predict sound propagation at the ranges studied here.

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Section: Introductionmentioning

confidence: 88%

Effects of strong sound velocity gradients on propagation of low-frequency impulse sound: Comparison of fast field program predictions and experimental data

Hole

Lunde

Gjessing³

1997

The Journal of the Acoustical Society of America

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“…To this end, our purposes here will be to integrate the analyses of Wenzel 3 and Chunchuzov 23 and to see if the generalized result is consistent with data from the Medicine Bow wind turbine. 25 …”

Section: Nomenclaturementioning

confidence: 97%

“…The source field expressed in terms of elementary waves with variable amplitude is . s yikz\z-Zs\ (25) As the wind speed approaches zero, the wave amplitudes approach unity, and the source field expression reduces to its known form without flow. As a function of wave number, the source field expression has poles at the integer values of v. The Bessel function solutions show these poles clearly.…”

Section: Source Fieldmentioning

confidence: 98%

Downwind sound propagation in an atmospheric boundary layer

Zorumski

Willshire

1989

AIAA Journal

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A theoretical analysis is given for an acoustic monopole in an atmospheric boundary layer. The analysis is based on the Obukhov quasipotential function (which defines both acoustic pressure and velocity) and assumes an isothermal atmosphere, an exponential boundary-layer flow profile, and a ground impedance function. It is shown that acoustic waves in the boundary layer can be represented by plane waves with variable amplitude. The wave amplitudes are given by the generalized hypergeometric function oFj. The present work is an extension of previous work by Wenzel, who studied surface waves associated with a ground plane without flow, and by Chunchuzov, who identified a discrete mode spectrum in an exponential boundary layer over a hard surface. It is shown that downwind propagation of low-frequency sound can be represented by these discrete modes, which spread as cylindrical waves. The downwind attenuation of the fundamental mode is proportional to frequency squared, wind speed, boundary-layer displacement thickness, and the real part of the ground admittance. The analysis is supported by acoustic data from a wind turbine at Medicine Bow, Wyoming. Nomenclaturetraveling wave amplitude c = speed of sound / = frequency F = upward-traveling wave, Ae + ikzZ &Fi = generalized hypergeometric function G = downward-traveling wave, Be~i kzZ J v -Bessel function of the first kind k -plane wave number co/c k x ,k y ,k z = wave numbers in x, y, and z directions L = boundary condition operator M = Mach number p -acoustic pressure p v = first Bessel function cross product q v = second Bessel function cross product Q = volumetric source strength r, 6,z = cylindrical coordinates R = spherical radius SPL = sound pressure level t = time u t v, w = acoustic velocities in x, y, and z directions, respectively U -wind velocity W[F,G} = Wronskian of F and G x,y,z = rectangular coordinates, downwind, cross wind, and vertical, respectively Y v = Bessel function of the second kind a. = plane wave attenuation coefficient or downwind attenuation j8 = specific ground admittance T(z) = complex gamma function d\ -boundary-layer displacement thickness e = strip width parameter f = waveguide coordinate 9 = standing wave function v = Wronskian p = density £ = strip coordinatê = Obukhov quasipotential co = circular frequency toy = boundary-layer vorticity Subscripts m n 5 x,r 0 oo-mode index = harmonic number = source position = in the respective coordinate direction = on the ground, z = 0 = above the boundary layer, z^°°I ntroduction T HIS paper will analyze the acoustic field of a source in an atmospheric boundary layer and compare the analysis to the downwind propagation of noise from a wind turbine. The dependent acoustic variable used is the Obukhov quasipotential function, 1 an extension of the conventional acoustic potential 2 which accounts for the effect of steady flow vorticity in the acoustic momentum equation. The analytical model is that of an acoustic monopole above a ground plane with a finite acoustic impedance. 2 The wind boundary ...

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The acoustic field of a point source in a uniform boundary layer over an impedance plane

Cited by 2 publications

References 2 publications

Effects of strong sound velocity gradients on propagation of low-frequency impulse sound: Comparison of fast field program predictions and experimental data

Effects of strong sound velocity gradients on propagation of low-frequency impulse sound: Comparison of fast field program predictions and experimental data

Downwind sound propagation in an atmospheric boundary layer

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