Spatial waves of higher modes in an axisymmetric turbulent jet

Chan, Y. Y.

doi:10.1063/1.861404

Cited by 10 publications

(9 citation statements)

References 4 publications

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“…Section 3 describes experiments where the jet is excited internally by a very low level acoustic wave, which appears to act as a trigger for vortex formation and so produce regular structure, locked to the excitation. The behaviour of this structure is like that of a natural disturbance on the jet and is not inconsistent with the motions described by the shear-layer stability theory of Michalke (197 1 a, b, 1972) and Chan (1975). At higher levels of excitation the instability wave on the shear layer becomes nonlinear.…”

Section: Introductionsupporting

confidence: 70%

The role of shear-layer instability waves in jet exhaust noise

1977

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Large-scale structures in the form of instability waves are an inherent part of a shearlayer mixing process. Such structures are shown to be present in an acoustically and aerodynamically well behaved jet even at high Mach numbers. They do not directly radiate significant acoustic power in a subsonic jet, but do govern the production of the turbulent fluctuations which radiate broad-band jet noise. Over the whole subsonic Mach number range, a significant increase in jet noise can be produced by exciting the shear layer with a fluctuating pressure at the nozzle of only 0·08 % of the jet dynamic head but with the correct Strouhal number. Such excitation by internal acoustic, aerodynamic or thermal fluctuations could explain the variability of jet noise measurements between different rigs and could also be responsible for some components of ‘excess’ noise.

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Section: Introductionsupporting

confidence: 70%

The role of shear-layer instability waves in jet exhaust noise

1977

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“…For a heated subsonic jet with exit Mach number 0.7 and exit temperature 9 0 0 K , Dahan & alias (1976) determined that noise was radiated from large-scale motions of the jet which had the local characteristics of wavelike instabilities of the jet. Chan (1974a, b ;1976) and Moore (1977) have demonstrated that it is possible to excite instability waves in the shear layer of a turbulent subsonic jet. Further, when the amplitudes of the excited waves were small, they found that most of their characteristics agreed quite well with the predictions of classical linear inviscid hydrodynamic-instability theory.…”

Section: Introductionmentioning

confidence: 99%

“…I n recent years a number of workers have examined the jet flow or free shear-layer instability problem. Some of the more recent works, such as those by Morris (1974Morris ( , 1976aMorris ( , 1977, Liu (1974), Tam (1975), Chan (1975), Merkine & Liu (1975), and others emphasized the slight nonlinear aspects of the problem. On the other hand, a number of papers such as those by Bouthier (1972Bouthier ( , 1973, Gaster (1974), Saric & Nayfeh (1975) and Crighton & Gaster (1976) discuss the modification to classical instability theory due to slight flow divergence which is inevitable in unbounded shear flows.…”

Section: Introductionmentioning

confidence: 99%

The radiation of sound by the instability waves of a compressible plane turbulent shear layer

1980

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The problem of acoustic radiation generated by instability waves of a compressible plane turbulent shear layer is solved. The solution provided is valid up to the acoustic far-field region. It represents a significant improvement over the solution obtained by classical hydrodynamic-stability theory which is essentially a local solution with the acoustic radiation suppressed. The basic instability-wave solution which is valid in the shear layer and the near-field region is constructed in terms of an asymptotic expansion using the method of multiple scales. This solution accounts for the effects of the slightly divergent mean flow. It is shown that the multiple-scales asymptotic expansion is not uniformly valid far from the shear layer. Continuation of this solution into the entire upper half-plane is described. The extended solution enables the near-and far-field pressure fluctuations associated with the instability wave to be determined. Numerical results show that the directivity pattern of acoustic radiation into the stationary medium peaks at 20 degrees to the axis of the shear layer in the downstream direction for supersonic flows. This agrees qualitatively with the observed noise-directivity patterns of supersonic jets.

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“…These eddies or waves would occur and interact randomly in space and time in a natural flow (without excitation). Their detection would thus require conditional sampling or straightforward Fourier decomposition (Wills 1964; Morrison & Kronauer 1970;Clark 1979). I n either case, interpretations of the results are not free from ambiguity.…”

Section: Introductionmentioning

confidence: 99%

“…Parenthetically, recognizing some of the limitations of the shear wave representation of the jet near-field flow structure, investigations based on flow-visualization and conditionally sampled hot-wire measurements were started in parallel Hussain & Zaman 1975Sokolov et al 1980;Clark 1979). It is believed that these two complementary approaches have unveiled significant new information on the physics of jet flows.…”

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confidence: 99%

Controlled symmetric perturbation of the plane jet: an experimental study in the initial region

Hussain

Thompson

1980

J. Fluid Mech.

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The response of the near field of a free, plane air jet (aspect ratio 44:1) to a controlled, sinusoidal perturbation was investigated by hot-wire measurements. The experiments were carried out at an exit excitation amplitude of 1·4 % for the Strouhal number range 0·15 [les ] StH [les ] 0·6 and the Reynolds-number range 8 × 103 [les ] ReH [les ] 3·1 × 104. The influence of the excitation, introduced with a loudspeaker attached to the jet settling chamber, on the mean and fluctuating velocity fields is much weaker than that in the circular jet. The amplitude and phase profiles of the fundamental, educed through phase-locked measurements, show that the induced symmetric mode remains symmetric as it travels downstream. The wave growth rate is much higher and the wavelength much smaller in the shear layer than on the centre-line of the jet. The wave fundamental attains its maximum amplitude at StH ≃ 0·18 on the jet centre-line and at StH ≃ 0·45 in the shear layer. The amplitude profiles of the fundamental in the shear layer agree quite well with the spatial stability theory of Michalke (1965b); however, the phase data do not agree well with the theoretical predictions. The growth rate and the disturbance wavenumber increase monotonically with the StH both in the shear layer and on the centre-line but tend to approach constant values at higher StH. The phase velocity data show that, in the lower Strouhal-number range, the plane jet acts as a non-dispersive waveguide.

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Spatial waves of higher modes in an axisymmetric turbulent jet

Abstract: It is shown theoretically that higher modes of wave-like disturbances can be propagated in the turbulent shear layer of an axisymmetric jet. Both the amplitudes and the extent of the spatially growing waves decrease as the order of the mode increases.

Cited by 10 publications

References 4 publications

The role of shear-layer instability waves in jet exhaust noise

The role of shear-layer instability waves in jet exhaust noise

The radiation of sound by the instability waves of a compressible plane turbulent shear layer

Controlled symmetric perturbation of the plane jet: an experimental study in the initial region

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