Continuation of Near-Acoustic Fields of Jets to the Far Field. Part I: Theory

Tam, Christopher K. W.; Pastouchenko, Nikolai; Viswanathan, K.

doi:10.2514/6.2010-3728

Cited by 16 publications

(14 citation statements)

References 32 publications

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“…Harker et al [6] confirmed this to be true by demonstrating that the negative loops are present in the autocorrelation function obtained from the analytical similarity spectrum associated with the large-scale structures. A limited analysis of the autocorrelation of select F-22A waveforms indicated the presence of negative loops at downstream distances, similar to those seen in laboratory-scale cases [1,3,19]. However, there are features in the full-scale data that are not seen in the laboratoryscale cases.…”

Section: Autocorrelation Measurementsmentioning

confidence: 62%

“…First, the width of the peak in the autocorrelation is considerably narrower to the sideline than in the aft direction. This argument was used by Kumar et al [19] and by Tam et al [1,3] to indicate that large-scale turbulent structures generated the noise at the aft angles and that the randomness at sideline angles is indicative of fine-scale structures. However, it has been shown [6] that the autocorrelation-function width is strongly dependent on the spectral peak frequency, and scaling of the temporal axis by peak frequency causes the gross differences in the width of the autocorrelation function to disappear.…”

Section: Autocorrelation Measurementsmentioning

confidence: 99%

“…Furthermore, because jet-noise-source characteristics are imprinted on the radiated sound field [1], the spatiotemporal features found in the pressure field complement spectral analyses by providing a more complete understanding of the acoustic source, thereby assisting those who seek to more accurately replicate these environments analytically, numerically, and experimentally. For example, both two-point space-time pressure correlation functions [2][3][4][5] and the shape of single-point autocorrelation functions have been used to distinguish between the fine-vs large-scale nature of the jet-noise radiation [1,6]. These measurements have also been used to provide spatiotemporal length scales, either broadband [1] or band limited [7], which are useful in validating and improving jet-noise models [8][9][10].…”

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confidence: 99%

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Spatiotemporal-Correlation Analysis of Jet Noise from a High-Performance Military Aircraft

et al. 2016

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Correlation analyses of ground-based acoustic-pressure measurements of noise from a tethered F-22A provide insights into the sound-field characteristics with position and engine condition. Time-scaled single-point (auto) correlation functions show that, to the side of the nozzle exit, the temporal-correlation envelope decays rapidly, whereas the envelope decays more slowly in the maximum radiation region and farther downstream. This type of spatial variation has been previously attributed to a transition from fine-to large-scale mixing noise in laboratoryscale jets. Two-point space-time (cross) correlation functions demonstrate that noise from a single engine operating at intermediate power is similar to that from a heated, convectively subsonic laboratory-scale jet, whereas additional features are seen at afterburner, relative to supersonic laboratory jets. A complementary coherence analysis provides estimates of coherence lengths as a function of frequency and location. Acoustic coherence lengths across the ground microphone array are used to analyze one-dimensional, equivalent-source-coherence lengths obtained from the DAMAS-C beamforming algorithm. The source coherence reaches its maximum downstream of the maximum source level, suggesting that uncorrelated sources meaningfully contribute to the dominant source region. In addition to revealing further the nature of the sound field near an advanced tactical engine, the characteristics seen should be useful as a phenomenological comparison point for those trying to model military-scale results both experimentally and numerically.

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Section: Autocorrelation Measurementsmentioning

confidence: 62%

Section: Autocorrelation Measurementsmentioning

confidence: 99%

mentioning

confidence: 99%

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Spatiotemporal-Correlation Analysis of Jet Noise from a High-Performance Military Aircraft

et al. 2016

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“…Space limitation does not allow the inclusion of these materials in this paper. Interested readers may consult the recent work of Tam et al [20], [21].…”

Section: Introductionmentioning

confidence: 97%

Extension of the near acoustic field of a jet to the far field

Tam¹,

Pastouchenko²,

Viswanathan³

2010

Procedia Engineering

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“…a constant phase difference) between two points in the field. Correlation and coherence has been used to illustrate the fine-scale and large-scale nature of jet noise sources [12][13][14][15][16]. Figure 6(a) shows the cross-correlation between the 70° waveform with itself (the autocorrelation) and waveforms from the other two measurement locations.…”

Section: Cross Correlationmentioning

confidence: 99%