Acoustic intensity near a high-powered military jet aircraft

The Journal of the Acoustical Society of America

Neilsen

Sommerfeldt

et al. 2017

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The phase and amplitude gradient estimator (PAGE) method for active acoustic intensity uses pairwise microphone transfer functions to obtain the phase gradient, which improves the calculation bandwidth over the traditional weighted quadspectral method. Additionally, for broadband sources, the PAGE theory indicates that the transfer function phase can be unwrapped to further extend the usable frequency range to beyond the spatial Nyquist frequency. Here, two experiments demonstrate intensity bandwidth extension by more than an order of magnitude using phase unwrapping. First, plane-wave tube results show accurate one-dimensional intensity calculations with the microphones separated by five wavelengths, 30 times the traditional limit. Second, two-dimensional measurements of a laboratory-scale jet with a four-microphone probe yield physically reasonable calculations at frequencies 15 times the traditional limit.

Section: Introductionmentioning

confidence: 99%

Experimental validation of acoustic intensity bandwidth extension by phase unwrapping

The Journal of the Acoustical Society of America

Neilsen

Sommerfeldt

et al. 2017

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“…The rocket intensity field exhibits two important differences from the prior intensity work of Stout et al 25,26) on an installed, afterburning military jet engine. First, there is not a significant overall contraction in peak source region extent with increasing frequency.…”

Section: Gem-60 Intensity Analysismentioning

confidence: 69%

“…From the linear array of probes parallel to the shear layer, intensity vectors that have magnitudes within 3 dB of the maximum (the "3-dB down region") are ray-traced back to the centerline to find an estimated dominant source region (green box) and a peak directivity angular range, which is defined by the range of angles denoted by the red lines. This approach has been recently applied by Stout et al 25,26) in source characterization of F-22A Raptor noise and was adapted from jet noise intensity characterizations by Jaeger and Allen. 27) The results of the ray-tracing are compiled in Fig.…”

Section: Gem-60 Intensity Analysismentioning

confidence: 99%

Development of a Near-field Intensity Measurement Capability for Static Rocket Firings

AEROSPACE TECHNOLOGY JAPAN

Whiting

Neilsen

et al. 2016

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Near-field characterization of the acoustical environment near rockets has often involved extrapolating far-field measurements. However, because far-field amplitude data reveals only limited information about source characteristics, a vector intensity measurement system and analysis package has been developed to examine source features more directly. This paper describes the development of the measurement and analysis capability and its application to a horizontal firing of a GEM-60 solid propellant rocket motor firing conducted at ATK Space Systems near Promontory, Utah. An analysis of near-field intensity data provides insight both into the spatial extent and principal radiation lobe as a function of frequency. For 50 Hz, the far-field spectral peak frequency in the maximum radiation direction, the dominant source region derived from tracing the near-field intensity vectors spans 17-32 nozzle diameters, with peak radiation at ~68 o . At high frequencies, the radiation results from a more contracted region that occurs farther upstream and is directed at about ~85°. These results point to the potential utility of near-field vector intensity measurements, in part because the near-field environments represented do not agree with historical far-field data-based models.

“…It is important to note that the microphone separation used to obtain broadband intensity is relatively large; microphone separations of 25-50 mm have been used previously for full-scale military jet engines 22,23 and even largerscale solid rocket motor tests 19,20,21 . The ability to extract time-averaged phase relationships and produce intensity vectors in the near field from microphones that are ultimately multiple wavelengths apart is unique and shows the utility of phase unwrapping for extending probe bandwidth well beyond traditional limits for broadband sources.…”

Section: A Page Phase Unwrappingmentioning

confidence: 99%

“…This paper describes the application of the recently developed phase and amplitude gradient estimator (PAGE) method 17,18 for calculating vector acoustic intensity to the wideband near-field characterization of a laboratory-scale supersonic jet. The present study builds upon the original Jaeger and Allen study of unheated jets and more recent efforts to characterize full-scale rocket plume 19,20,21 and military jet engine 22,23 noise environments. The intensity method is first summarized, followed by a description of the experimental facilities and measurement performed.…”

Section: Introductionmentioning

confidence: 99%

Characterization of Supersonic Laboratory-Scale Jet Noise with Vector Acoustic Intensity

23rd AIAA/CEAS Aeroacoustics Conference

Akamine

Okamoto

et al. 2017

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A new method for the calculation of vector acoustic intensity from pressure microphone measurements has been applied to the aeroacoustic source characterization of an unheated, Mach 1.8 laboratory-scale jet. Because of the ability to unwrap the phase of the transfer functions between microphone pairs in the measurement of a radiating, broadband source, physically meaningful near-field intensity vectors are calculated up to the maximum analysis frequency of 32 kHz. The new intensity method is used to obtain a detailed description of the sound energy flow near the jet. The resulting intensity vectors have been used with a raytracing technique to identify the dominant source region over a broad range of frequencies. Additional aeroacoustics analyses provide insight into the frequency-dependent characteristics of jet noise radiation, including the nature of the hydrodynamic field and the transition between the principal lobe and sideline radiation. Nomenclature d = spacing between two microphones = nozzle exit diameter , = transfer function between microphones a and b I = time-averaged vector intensity p = acoustic pressure = acoustic pressure magnitude = acoustic pressure phase , ( ) = quadspectrum between microphones a and b 1 Associate Professor, Dept. of Physics and Astronomy, N283 ESC, AIAA Senior Member.