Calculations of far-field and near-field jet noise

1975 ◽  
Author(s):  
C.-Y. CHEN
Keyword(s):  
Near Field ◽  
Jet Noise ◽  
Far Field

Simultaneous Noise and Performance Measurements for High-Speed Jet Noise Reduction Technologies

2009 ◽  
Author(s):  
Dean Long ◽  
Steven Martens
Keyword(s):  
Noise Reduction ◽  
High Speed ◽  
Near Field ◽  
Jet Noise ◽  
Source Distribution ◽  
Test Facility ◽  
Wave Radiation ◽  
Far Field ◽  
Shock Cell ◽  
Field Noise

Model scale tests are conducted to assess the Noise/Performance trade for high speed jet noise reduction technologies. It is demonstrated that measuring the near field acoustic signature with a microphone array can be used to assess the far field noise using a procedure known as acoustic holography. The near field noise measurement is mathematically propagated producing an estimate of the noise level at the new location. Outward propagation produces an estimate of the far field noise. Propagation toward the jet axis produces the source distribution. Tests are conducted on convergent/divergent nozzles with three different area ratios, and several different chevron geometries. Noise is characterized by two independent processes: Shock cell noise radiating in the forward quadrant is produced when the nozzle is operated at non-ideally expanded conditions. Mach wave radiation propagates into the aft quadrant when the exhaust temperature is elevated. These results show good agreement with actual far field measurements from tests in the GE Cell 41 Acoustic Test Facility. Simultaneous performance measurement shows the change in thrust coefficient for different test conditions and configurations. Chevrons attached to the nozzle exit can reduce the noise by several dB at the expense of a minimal thrust loss.

On the Connection Between Near-Field and Far-Field Solutions of High-Speed Jet Noise

2008 ◽  
Author(s):  
Foluso Ladeinde ◽  
Xiaodan Cai ◽  
Ken Alabi ◽  
Ramons Reba ◽  
Robert Schlinker ◽  
...  
Keyword(s):  
High Speed ◽  
Near Field ◽  
Jet Noise ◽  
Far Field

Experimental Study of the Properties of Near-Field and Far-Field Jet Noise

2006 ◽  
Author(s):  
Sébastien Barré ◽  
Vincent Fleury ◽  
Christophe Bogey ◽  
Christophe Bailly ◽  
Daniel Juve
Keyword(s):  
Experimental Study ◽  
Near Field ◽  
Jet Noise ◽  
Far Field

scholarly journals Experimental Study of the Spectral Properties of Near-Field and Far-Field Jet Noise

2007 ◽  
Vol 6 (2) ◽  
pp. 73-92 ◽  
Author(s):  
Christophe Bogey ◽  
Sébastien Barré ◽  
Vincent Fleury ◽  
Christophe Bailly ◽  
Daniel Juvé
Keyword(s):  
Experimental Study ◽  
Spectral Properties ◽  
Near Field ◽  
Jet Noise ◽  
Far Field

A Surface-Integral Formulation for Jet Noise Prediction Based on the Pressure Signal Alone

1998 ◽  
Vol 06 (03) ◽  
pp. 307-320 ◽  
Author(s):  
R. R. Mankbadi ◽  
S. H. Shih ◽  
D. R. Hixon ◽  
J. T. Stuart ◽  
L. A. Povinelli
Keyword(s):  
Cylindrical Surface ◽  
Large Scale ◽  
Near Field ◽  
Jet Noise ◽  
Normal Derivative ◽  
Integral Formulation ◽  
Noise Prediction ◽  
Far Field ◽  
Surface Integral ◽  
Large Scale Simulation

While large-scale simulation of jet noise is the most thorough technique currently available for jet noise prediction, three-dimensional direct computation of both the near and far field requires prohibitive computational capability. In this work we propose to limit large-scale simulation to the near field to provide the pressure distribution over a cylindrical surface surrounding the jet. A surface-integral formulation is presented herein in which the calculated pressure on the cylindrical surface is used to obtain the far-field sound, without the need for the normal derivative of the pressure. The results are compared to that of direct large-scale simulation and to the zonal approach in which linearized Euler equations are used as an extension tool.

Simultaneous Noise and Performance Measurements for High Speed Jet Noise Reduction Technologies: Part II—Near Field Array Calibration

2011 ◽  
Author(s):  
Dean Long ◽  
Steve Martens
Keyword(s):  
Noise Reduction ◽  
High Speed ◽  
Near Field ◽  
Jet Noise ◽  
Source Distribution ◽  
Wave Radiation ◽  
Far Field ◽  
Performance Measurements ◽  
Shock Cell ◽  
Field Noise

Part I of this paper describes a methodology for assessing the far field jet noise from high speed exhaust nozzles using a microphone array in the near field of the exhaust plume. The near field noise measurement is mathematically propagated producing an estimate of the noise level at the new location. Outward propagation produces an estimate of the far field noise. Propagation toward the jet axis produces the source distribution. Part II described here provides a direct validation of this process using a generic CD nozzle in a facility where both the near field and the far field are measured simultaneously. Comparison of these data sets show good agreement over the typical operating range for this type of nozzle. The far field noise is characterized by two independent processes: Shock cell noise radiating in the forward quadrant is produced when the nozzle is operated at non-ideally expanded conditions. Mach wave radiation propagates into the aft quadrant when the exhaust temperature is elevated. Subsequent tests in an acoustically treated nozzle thrust stand demonstrate the value of the near field array allowing immediate feedback on the noise/performance tradeoff for high speed jet noise reduction technologies.

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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