Journal ArticleDOI
The near pressure field of co-axial subsonic jets
Charles E. Tinney,Peter Jordan +1 more
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In this paper, an analysis of the axial, temporal and azimuthal structure of the pressure field of a co-axial jet with and without serrations on the secondary nozzle lip is presented.Abstract:
Results are presented from pressure measurements performed in the irrotational near field of unbounded co-axial jets. Measurements were made for a variety of velocity and temperature ratios, and configurations both with and without serrations on the secondary nozzle lip. The principal objective of the study is to better understand the near pressure field of the jet, what it can tell us regarding the underlying turbulence structure, and in particular how it can be related to the source mechanisms of the flow.A preliminary analysis of the axial, temporal and azimuthal structure of the pressure field shows it to be highly organized, with axial spatial modes (obtained by proper orthogonal decomposition) which resemble Fourier modes. The effects of serrations on the pressure fluctuations comprise a global reduction in level, a change in the axial energy distribution, and a modification of the evolution of the characteristic time scales.A further analysis in frequency–wavenumber space is then performed, and a filtering operation is used to separate the convective and propagative footprints of the pressure field. This operation reveals two distinct signatures in the propagating component of the field: a low-frequency component which radiates at small angles to the flow axis and is characterized by extensive axial coherence, and a less-coherent high-frequency component which primarily radiates in sideline directions. The serrations are found to reduce the energy of the axially coherent propagating component, but its structure remains fundamentally unchanged; the high-frequency component is found to be enhanced. A further effect of the serrations involves a relative increase of the mean-square pressure level of the acoustic component – integrated over the measurement domain – with respect to the hydrodynamic component. The effect of increasing the velocity and temperature of the primary jet involves a relative increase in the acoustic component of the near field, while the hydrodynamic component remains relatively unchanged: this shows that the additional acoustic energy is generated by the mixing region which is produced by the interaction of the inner and the outer shear layers, whereas the hydrodynamic component of the near field is primarily driven by the outer shear layer.read more
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Journal ArticleDOI
Spectral proper orthogonal decomposition and its relationship to dynamic mode decomposition and resolvent analysis
TL;DR: In this article, the spectral proper orthogonal decomposition (SPOD) has been studied in the context of the analysis of the Ginzburg-Landau equation and a turbulent jet.
Journal ArticleDOI
Instability wave models for the near-field fluctuations of turbulent jets
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Wavepackets in the velocity field of turbulent jets
TL;DR: In this article, the velocity field of unforced, high Reynolds number, subsonic jets, issuing from round nozzles with turbulent boundary layers, is measured using a hot-wire anemometer and a stereoscopic, time-resolved PIV system.
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Axisymmetric superdirectivity in subsonic jets
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Jittering wave-packet models for subsonic jet noise
TL;DR: In this paper, three simplified wave-packet models of the coherent structures in subsonic jets are presented, and the dependence of the radiated sound on the temporal variations of the amplitude and spatial extent of the modulations are studied separately in the first two model problems, being considered together in the third.
References
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Velocity dependence of the near pressure field of subsonic jets: understanding the associated source mechanisms.
TL;DR: In this paper, an empirical relationship is established which demarcates the space-frequency limits of the hydrodynamic and acoustic components as a function of the exit velocity of a subsonic jet.
Proceedings ArticleDOI
Computation of the Flow and Noise of Round and Beveled Nozzles
TL;DR: In this article, numerical simulations of the flow field and the noise generated by round and beveled nozzles are carried out, with the goal of gaining insights into the flow features that are responsible for noise generation.
Proceedings ArticleDOI
Low-dimensional signatures of the sound production mechanisms in subsonic jets: Towards their identification and control
TL;DR: In this article, the low-dimensional building-blocks of the pressure and velocity fields of a subsonic jet were extracted by means of joint Proper Orthogonal, Fourier- azimuthal Decompositions, and studied with a view to understanding their respective roles in the production of jet noise.
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