Acoustical Nonlinearities in Aircraft Flyover Data

Sally, M; Gee, Kent L.; Downing, Micah; James, Michael M.; Ridge, Blue

doi:10.2514/6.2007-3654

Cited by 21 publications

(23 citation statements)

References 21 publications

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“…(21) and (22). The forward difference estimate of the slope of the discretely sampled Khokhlov solution at Àp < s < p, which is needed to solve the integrals in Eqs.…”

Section: Khokhlov Solutionmentioning

confidence: 99%

“…Rudenko and Chirkin 17 and Webster and Blackstock 18 showed that the probability density function of the waveform remains stationary until shocks form, which suggests that useful measures might be based on the temporal rates of change of the pressure. The statistics (i.e., skewness and/or kurtosis) of the waveform time derivative have been used to characterize the nonlinearity for initial sinusoids, 19 noise in a plane-wave tube, 20 and jet 10,[21][22][23][24][25][26] and rocket 27,28 noise. Baars and Tinney 11 have recently investigated a shock detection algorithm in the context of supersonic jet noise propagation for such metrics as number of shocks per unit time.…”

Section: Introductionmentioning

confidence: 99%

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Evolution of the average steepening factor for nonlinearly propagating waves

Muhlestein

Gee

Neilsen

et al. 2015

The Journal of the Acoustical Society of America

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Difficulties arise in attempting to discern the effects of nonlinearity in near-field jet-noise measurements due to the complicated source structure of high-velocity jets. This article describes a measure that may be used to help quantify the effects of nonlinearity on waveform propagation. This measure, called the average steepening factor (ASF), is the ratio of the average positive slope in a time waveform to the average negative slope. The ASF is the inverse of the wave steepening factor defined originally by Gallagher [AIAA Paper No. 82-0416 (1982)]. An analytical description of the ASF evolution is given for benchmark cases-initially sinusoidal plane waves propagating through lossless and thermoviscous media. The effects of finite sampling rates and measurement noise on ASF estimation from measured waveforms are discussed. The evolution of initially broadband Gaussian noise and signals propagating in media with realistic absorption are described using numerical and experimental methods. The ASF is found to be relatively sensitive to measurement noise but is a relatively robust measure for limited sampling rates. The ASF is found to increase more slowly for initially Gaussian noise signals than for initially sinusoidal signals of the same level, indicating the average distortion within noise waveforms occur more slowly.

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“…(21) and (22). The forward difference estimate of the slope of the discretely sampled Khokhlov solution at Àp < s < p, which is needed to solve the integrals in Eqs.…”

Section: Khokhlov Solutionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Evolution of the average steepening factor for nonlinearly propagating waves

Muhlestein

Gee

Neilsen

et al. 2015

The Journal of the Acoustical Society of America

View full text Add to dashboard Cite

show abstract

“…[1][2][3] In particular, the appearance of multiple peaks in the acoustic far-field spectra of the jet mixing noise is predominantly a characteristic of full-scale tactical jets. [1][2][3][4][5][6][7][8][9] The acoustical nature of the radiation lobes that generate these peaks is the focus of the current paper.…”

Section: Introductionmentioning

confidence: 99%

Investigation of multi-lobed fighter jet noise sources using acoustical holography and partial field decomposition methods

Wall

Gee

Neilsen

et al. 2015

21st AIAA/CEAS Aeroacoustics Conference

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Full-scale tactical aircraft noise exhibits multiple radiation lobes not seen in laboratoryscale jets. These lobes have different radiation directions yet appear to have similar, overlapping source regions. Near-field acoustical holography (NAH) source reconstructions, in conjunction with partial field decomposition (PFD) methods that produce physically meaningful partial fields, are used in the current work to investigate the nature of these radiation patterns. First, it is shown that the two main radiation lobes are highly incoherent, suggesting independent partial sources. Second, these lobes are isolated as mutually orthogonal partial fields. In this representation, the lobes seem to be generated by independent yet spatially coincident extended partial sources. Source comparisons are made between non-afterburner and afterburner engine powers to investigate whether afterburner combustion produces any sources that are fundamentally different from those of nonafterburner operations. The current results show no qualitative changes occur due to the addition of the afterburner thrust aside from minor variations in source distribution, level, and the nature of the overlap between the multiple lobes.

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“…The effect has been studied in jet aircraft noise propagation, where it has been demonstrated that nonlinear effects are responsible for the higher values measured at high frequencies compared to the values predicted using linear propagation theory. [1][2][3][4] Literature on nonlinear propagation of helicopter noise is far less extensive. Nonlinear distortion has been considered insignificant for helicopter noise, as the noise field produced by a helicopter rotor is, in general, of relatively low intensity ͑compared to the noise field produced by a jet aircraft͒.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigation of nonlinear propagation distortion effects in helicopter rotor noise

Menounou

Vitsas

2009

The Journal of the Acoustical Society of America

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The effect of nonlinear propagation distortion on helicopter rotor noise is presented based on measured data for low-speed descent and numerical calculations that predict the noise level away from the helicopter with and without nonlinear effects. It is shown that for some frequency bands the difference between linear and nonlinear calculations can be as high as 7 dB. Blade vortex interaction (BVI) noise, the dominant noise contributor during descent, is mainly examined. It is shown that advancing side BVI noise is affected by nonlinear distortion, while retreating side BVI noise is not. Based on signal characteristics at source, two quantities are derived. The first quantity (termed polarity) is based on the pressure gradient of the source signal and can be used to determine whether a BVI signal will evolve as an advancing or a retreating side signal. The second quantity (termed weighted rise time) is a measure of the impulsiveness of the BVI signal and can be used to determine at which frequency nonlinear effects start to appear. Finally, polarity and weighted rise time are shown to be applicable in cases of BVI noise generated from different blade tips, as well as in cases of non-BVI noise.

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Acoustical Nonlinearities in Aircraft Flyover Data

Cited by 21 publications

References 21 publications

Evolution of the average steepening factor for nonlinearly propagating waves

Evolution of the average steepening factor for nonlinearly propagating waves

Investigation of multi-lobed fighter jet noise sources using acoustical holography and partial field decomposition methods

Numerical investigation of nonlinear propagation distortion effects in helicopter rotor noise

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