Acoustic ray method derived with the concept of analogue gravity for the calculation of the sound field due to rotating sound sources

Ocker, Christof; Pannert, Wolfram

doi:10.1016/j.apacoust.2020.107422

Cited by 8 publications

(5 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…8b), but to greater radii, a cusp is formed. The cusp singularity is produced at the position r cusp = q s /M 0 = 0.67 m. A more detailed discussion on the Mach cone at circular motion is presented by Lowson and Jupe [22], Poletti [7], and Ocker and Pannert [23].…”

Section: Supersonic Rotationmentioning

confidence: 99%

Three-dimensional acoustic energy flow from rotating sound sources

Ocker

Pannert

2021

Acta Acust.

Self Cite

View full text Add to dashboard Cite

A detailed study of the three-dimensional sound fields around a monopole point source in subsonic and supersonic rotation is investigated. We calculate the sound pressure, the acoustic velocity, as well as the instantaneous and time-averaged acoustic intensity fields with the advanced time approach. The advanced time approach is applied for sound sources at subsonic and supersonic rotation and yield comparable results as those obtained from the spherical harmonic series expansion method or the solution of the retarded time equation. Further, the direction of the time-averaged acoustic energy flow is derived from the acoustic intensity vectors. It is shown, that the direction of the energy flow path differs from the radial direction and depends on the rotational direction and rotational velocity. Those findings are useful, for example, to improve the acoustic absorption performance of sound absorbers and acoustic liners around turbomachines.

show abstract

Section: Supersonic Rotationmentioning

confidence: 99%

Three-dimensional acoustic energy flow from rotating sound sources

Ocker

Pannert

2021

Acta Acust.

Self Cite

View full text Add to dashboard Cite

show abstract

“…Therefore, as a second step, the sound sources are localized with a microphone array. The sound field in the rotating frame of reference is calculated with the acoustic ray method (ARM) [34] and the modal decomposition method in combination with Daniell's method [35] is used to calculate microphone auto and cross spectra in the rotating frame of reference. Then, CLEAN-SC is applied to the beamformer output to improve the resolution and the dynamic range of the acoustic source maps [36].…”

Section: Sound Source Localizationmentioning

confidence: 99%

Aerodynamic and aeroacoustic properties of axial fan blades with slitted leading edges

et al. 2022

View full text Add to dashboard Cite

A detailed experimental analysis of the aerodynamic and aeroacoustic properties of flat-plate axial fans with slitted leading edges is performed. The sound emissions of five slitted leading edge designs are measured at a constant rotational speed and at a constant total-to-static pressure rise of the fans. For both cases, the fan blades with slitted leading edges reduce the turbulence interaction noise and lead to a reduction of the overall sound pressure level for volume flow rates above 0.6 m3 s−1 compared to an axial fan with solid leading edges. The far-field noise analysis shows that the slits result in a noise reduction for frequencies below 2 kHz and a noise increase above 2 kHz. In addition, sound source localization is conducted with a microphone array and rotating beamforming methods are applied. The identified sound source distributions prove that slitted leading edges reduce turbulence interaction noise, but generate broadband noise in the fan blades’ trailing edge regions. The maximum sound reduction due to the slits could be detected at a dimensionless frequency of $ fh/\bar{w}\approx 0.5$, where f is the frequency, h is the height of the slit and $ \bar{w}$ is the mean relative inflow velocity. The noise reduction mechanism on axial fan blades corresponds well to previous investigations on flat-plate airfoils with slits.

show abstract

“…The calculation of the sound field in the rotating frame of reference is based on the acoustic ray method and follows the descriptions by Ocker and Pannert. 24 The microphone auto spectra and cross spectra were calculated via Fourier interpolation 40 and were averaged using Daniell's method to give the CSM. 41 For the acoustic source maps, the Clean-SC deconvolution method was applied to the beamformer output to improve the resolution of the sound sources.…”

Section: Data Evaluationmentioning

confidence: 99%

“…the spherical harmonic series expansion of the free-field Green's function, the ARM shows a high computational performance especially for the calculation of broadband noise. In Ocker and Pannert, 24 the derivation of the ARM is presented and validated against benchmark cases for rotating sound sources based on generic and measured time-signals. It is shown, that the localization of the sound sources with the ARM is in good correspondence to the localization with the spherical harmonic series expansion method, but the computational effort is much less.…”

Section: Sound Field In the Rotating Frame Of Referencementioning

confidence: 99%

“…For the de-Dopplerisation of the rotating noise sources, the recently developed acoustic ray method is used. 24 Then, a highresolution beamforming deconvolution method is applied and integration regions around the leading edge and trailing edge subregions of the wind turbine blades are defined to calculate the sound pressure levels of the sound sources, which only originate from a specific subregion. Other sound sources, for example, from the wind tunnel, are excluded from the integration.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Localization of wind turbine noise using a microphone array in wind tunnel measurements

Ocker

Blumendeller²,

Berlinger³

et al. 2021

Wind Energy

Self Cite

View full text Add to dashboard Cite

An experimental investigation on scaled wind turbine models in a wind tunnel with a microphone array is presented. Our study focuses on the localization and quantification of aerodynamic noise sources on rotating wind turbine blades with the aim of identifying the contributing factors that have an impact on the source spectra. Therefore, wind tunnel measurements were conducted for three different blade geometries (NACA 4412 shape, Clark-Y shape, and sickle shape), five pitch angles between À2 and +8 and five wind velocities between 5 and 13 ms ^À1 . For the localization of rotating sound sources with a microphone array, a rotating beamforming method based on the acoustic ray method is used. The Clean-SC deconvolution method was used to improve the resolution of the acoustic sources, and integrated spectra were calculated for the individual blades. The sound sources were localized at the wind turbine blades and assigned to the leading edge and trailing edge subregions. The results show a high dependency on the sound source distribution and the source strength with regard to the observed one-third octave bands, wind velocity, and blade geometry. Hence, the localization of rotating sound sources with a microphone array is a suitable method for the development of wind turbine blades that emit less noise.

show abstract

Acoustic ray method derived with the concept of analogue gravity for the calculation of the sound field due to rotating sound sources

Cited by 8 publications

References 20 publications

Three-dimensional acoustic energy flow from rotating sound sources

Three-dimensional acoustic energy flow from rotating sound sources

Aerodynamic and aeroacoustic properties of axial fan blades with slitted leading edges

Localization of wind turbine noise using a microphone array in wind tunnel measurements

Contact Info

Product

Resources

About