A Weak-Scattering Model for Turbine-Tone Haystacking outside the Cone of Silence

Powles, Christopher; Tester, Brian J.; McAlpine, Alan

doi:10.1260/1475-472x.10.1.17

Cited by 19 publications

(18 citation statements)

References 18 publications

(44 reference statements)

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“…some of the energy in the tone is scattered into adjacent frequency bands, but the total remains constant, then the out-of-flow microphones can be used to determine one-third octave band levels with good accuracy. Candel et al 10 gives some support for that assumption, at least for weak haystacking (Powles et al 11 ) where the scattered energy is small compared to that in the tone, but we are not aware of any theoretical or experimental proof that this is true in general. Figure 9, compares PWL measurements made using a representative microphone from the inflow traverse (black) and the out-of-flow fly-over array (red).…”

Section: Figure 8 Measured (Black) and Background (Green) Pwls Out-mentioning

confidence: 80%

Relative importance of open rotor tone and broadband noise sources

Kingan

Blandeau

Tester

et al. 2011

17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference)

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A study is made of the noise levels and spectral characteristics of three contra-rotating propeller rigs: rig 140 tested in 1989, rig 145 build 1 tested in 2008, and rig 145 build 2 tested in 2010. We use tone deletion techniques, applied to the inflow microphone data, to show the relative importance of propeller broadband noise to propeller tones with increasing frequency and, in particular, that by the time we reach only moderate frequencies, the one third octave spectra become dominated by the broadband noise components. We also show that the broadband noise continues to be important as blade speed and rig thrust are varied and that these spectral characteristics are present on both modern and older contra-rotating propeller designs -even those with a profusion of tones and strong tone protusion. We also show how the tone and broadband noise levels have reduced with more recent, and aeroacoustically improved, blade designs

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Section: Figure 8 Measured (Black) and Background (Green) Pwls Out-mentioning

confidence: 80%

Relative importance of open rotor tone and broadband noise sources

Kingan

Blandeau

Tester

et al. 2011

17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference)

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“…These configurations have also been studied analytically by Campos 5,6 who concluded that for an engine jet, widening the shear layer could significantly reduce tonal components propagating through the exhaust. Powles et al 25 and McAlpine et al 22 developed an analytical model to predict the haystacking of turbine tones. This model is able to consider frozen or evolving turbulence, and the variations of the source/flow parameters show behaviors of the spectra agreeing with existing experimental results.…”

Section: Introductionmentioning

confidence: 99%

Numerical assessment of the scattering of acoustic waves by turbulent structures

Clair

Gabard

2015

21st AIAA/CEAS Aeroacoustics Conference

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The scattering of harmonic sound waves by a single vortex is studied to provide some insight into the more complex problem of sound scattering by a turbulent layer. Two different methods are used to model the scattering by a steady vortex or by a vortex convected in a uniform mean flow. The first method is based on the linearized Euler equations in the frequency domain and is used to study the scattering by a steady vortex. The speed of this method allows to perform a study of the spatial scattering of a plane wave over a wide range of frequencies, where analytical models previously developed are restricted either to low or high frequencies. The second method uses a finite difference solver, also based on the linearized Euler equations but in the time domain. This method is used to study the scattering by a vortex convected in a uniform mean fow, where a spectral scattering occurs in addition to the spatial scattering. A parametric study is realized, focusing on four parameters including the source frequency and the convection velocity. The spectra deduced from this study show a pattern similar to the haystacking observed in existing studies of the scattering by a turbulent shear layer. Some of the trends deduced from the parametric study are also in agreement with these previous observations. Thus, the detailled study of the scattering by a single eddy is able to provide further understanding of the turbulence scattering.

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“…The apparent shift of source position at the scattered frequencies has not been investigated in detail before and is compared here with that obtained from the weak scattering relationship derived by Cargill, as noted by Powles et al 4 .…”

Section: Comparison Of Experimental Beamformer Results With Weak mentioning

confidence: 83%

“…The objective was to improve our understanding of the tone haystacking mechanisms with the aid of beamforming and the weak scattering theory proposed by Cargill 3 , as extended by Powles et al 4 and McAlpine et al 5 . Part II describes that experiment, Part III presents an analysis of the far-field and the beamformer data and Part IV describes a comparison of one aspect of the Cargill theory with the observations extracted from the processed beamformer data.…”

Section: Introductionmentioning

confidence: 99%

Measurement and analysis of phased array data on haystacked tones from a source located in a free jet

Tester

Sijtsma²

2017

23rd AIAA/CEAS Aeroacoustics Conference

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Significant spectral broadening of tone noise by jet shear-layer turbulence can occur if the tone frequency and the path length through the shear layer are sufficiently large. A typical example of spectral broadening or 'tone haystacking' are turbine aero-engine tones which exhibit little or no haystacking when measured inside the engine but are sometimes so strongly haystacked in the far-field that the original tone cannot be observed in the measured spectrum. This haystacking of turbine tones requires an engineering method that can predict both the far-field haystacking and the associated reduction in incident tone level. A previous published method, the so-called 'beta' correlation has displayed encouraging agreement with a number of experimental datasets but significant disagreement with others. In this paper another set of experimental data, which includes phased array data, is analysed. The objective is to improve our understanding of the tone haystacking mechanisms with the aid of beamforming and to compare with a prediction from weak scattering theory, in the form of a simple Doppler shift relationship between frequency and angle scattering, assuming a frozen turbulence model. The experimental data acquired by QinetiQ and CLEAN-SC beamformer results described herein begin to provide validation of that prediction, which may lead to resolution of the discrepancies previously observed between the beta correlation and the data acquired under a GARTEUR project.

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A Weak-Scattering Model for Turbine-Tone Haystacking outside the Cone of Silence

Cited by 19 publications

References 18 publications

Relative importance of open rotor tone and broadband noise sources

Relative importance of open rotor tone and broadband noise sources

Numerical assessment of the scattering of acoustic waves by turbulent structures

Measurement and analysis of phased array data on haystacked tones from a source located in a free jet

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