Nonlinear interaction model of subsonic jet noise

2008 ◽  
Vol 366 (1876) ◽  
pp. 2745-2760 ◽  
Author(s):  
Neil D Sandham ◽  
Adriana M Salgado
Keyword(s):  
Near Field ◽  
Sound Radiation ◽  
Jet Noise ◽  
Interaction Model ◽  
Simplified Model ◽  
Nonlinear Interactions ◽  
Radiation Characteristics ◽  
Instability Modes ◽  
Field Sound ◽  
Subsonic Jet

Noise generation in a subsonic round jet is studied by a simplified model, in which nonlinear interactions of spatially evolving instability modes lead to the radiation of sound. The spatial mode evolution is computed using linear parabolized stability equations. Nonlinear interactions are found on a mode-by-mode basis and the sound radiation characteristics are determined by solution of the Lilley–Goldstein equation. Since mode interactions are computed explicitly, it is possible to find their relative importance for sound radiation. The method is applied to a single stream jet for which experimental data are available. The model gives Strouhal numbers of 0.45 for the most amplified waves in the jet and 0.19 for the dominant sound radiation. While in near field axisymmetric and the first azimuthal modes are both important, far-field sound is predominantly axisymmetric. These results are in close correspondence with experiment, suggesting that the simplified model is capturing at least some of the important mechanisms of subsonic jet noise.

scholarly journals Near-field sound radiation of fan tones from an installed turbofan aero-engine

2015 ◽  
Vol 138 (3) ◽  
pp. 1313-1324 ◽  
Author(s):  
Alan McAlpine ◽  
James Gaffney ◽  
Michael J. Kingan
Keyword(s):  
Near Field ◽  
Sound Radiation ◽  
Aero Engine ◽  
Near Field Sound ◽  
Field Sound

scholarly journals Near-field Wavepackets and the Far-field Sound of a Subsonic Jet

2013 ◽  
Author(s):  
David E. Breakey ◽  
Peter Jordan ◽  
Andre Cavalieri ◽  
Olivier Léon
Keyword(s):  
Near Field ◽  
Far Field ◽  
Field Sound ◽  
Subsonic Jet

scholarly journals A coherence-matched linear source mechanism for subsonic jet noise

2015 ◽  
Vol 776 ◽  
pp. 235-267 ◽  
Author(s):  
Yamin B. Baqui ◽  
Anurag Agarwal ◽  
André V. G. Cavalieri ◽  
Samuel Sinayoko
Keyword(s):  
Linear Models ◽  
Hydrodynamic Instability ◽  
Near Field ◽  
Jet Noise ◽  
Turbulent Jets ◽  
Single Frequency ◽  
Linear Wave ◽  
Far Field ◽  
Potential Core ◽  
Subsonic Jet

We investigate source mechanisms for subsonic jet noise using experimentally obtained datasets of high-Reynolds-number Mach 0.4 and 0.6 turbulent jets. The focus is on the axisymmetric mode which dominates downstream sound radiation for low polar angles and the frequency range at which peak noise occurs. A linearized Euler equation (LEE) solver with an inflow boundary condition is used to generate single-frequency hydrodynamic instability waves, and the resulting near-field fluctuations and far-field acoustics are compared with those from experiments and linear parabolized stability equation (LPSE) computations. It is found that the near-field velocity fluctuations closely agree with experiments and LPSE computations up to the end of the potential core, downstream of which deviations occur, but the LEE results match experiments better than the LPSE results. Both the near-field wavepackets and the sound field are observed directly from LEE computations, but the far-field sound pressure levels (SPLs) obtained are more than an order of magnitude lower than experimental values despite close statistical agreement of the near hydrodynamic field up to the potential core region. We explore the possibility that this discrepancy is due to the mismatch between the decay of two-point coherence with increasing distance in experimental flow fluctuations and the perfect coherence in linear models. To match the near-field coherence, experimentally obtained coherence profiles are imposed on the two-point cross-spectral density (CSD) at cylindrical and conical surfaces that enclose near-field structures generated with LEEs. The surface pressure is propagated to the far field using boundary value formulations based on the linear wave equation. Coherence matching yields far-field SPLs which show improved agreement with experimental results, indicating that coherence decay is the main missing component in linear models. The CSD on the enclosing surfaces reveals that the application of a decaying coherence profile spreads the hydrodynamic component of the linear wavepacket source on to acoustic wavenumbers, resulting in a more efficient acoustic source.

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