Improved Phased Array Imaging of a Model Jet

Dougherty, Robert P.; Podboy, Gary G.

doi:10.2514/6.2009-3186

Cited by 56 publications

(46 citation statements)

References 22 publications

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“…A more expansive jet-noise array study is reported by Dougherty and Podboy 4 . A planar array was used in the Small Hot Jet Acoustic Rig (SHJAR) in the Aero-Acoustic Propulsion Laboratory at the NASA-Glenn Research Center.…”

Section: Introductionmentioning

confidence: 99%

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DAMAS Processing for a Phased Array Study in the NASA Langley Jet Noise Laboratory

Brooks

Humphreys

Plassman

2010

16th AIAA/CEAS Aeroacoustics Conference

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A jet noise measurement study was conducted using a phased microphone array system for a range of jet nozzle configurations and flow conditions. The test effort included convergent and convergent/divergent single flow nozzles, as well as conventional and chevron dual-flow core and fan configurations. Cold jets were tested with and without wind tunnel co-flow, whereas, hot jets were tested only with co-flow. The intent of the measurement effort was to allow evaluation of new phased array technologies for their ability to separate and quantify distributions of jet noise sources. In the present paper, the array post-processing method focused upon is DAMAS (Deconvolution Approach for the Mapping of Acoustic Sources) for the quantitative determination of spatial distributions of noise sources. Jet noise is highly complex with stationary and convecting noise sources, convecting flows that are the sources themselves, and shock-related and screech noise for supersonic flow. The analysis presented in this paper addresses some processing details with DAMAS, for the array positioned at 90° (normal) to the jet. The paper demonstrates the applicability of DAMAS and how it indicates when strong coherence is present. Also, a new approach to calibrating the array focus and position is introduced and demonstrated.

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Section: Introductionmentioning

confidence: 99%

“…TIDY (not fully documented at the time of Ref. 4) is stated to be similar philosophically to CLEAN-SC 5 , but operates in the time, rather than frequency, domain. The algorithms iteratively remove (by decomposition) side lobes and parts of the beamform solutions that are spatially coherent with the apparent peak sources.…”

Section: Introductionmentioning

confidence: 99%

DAMAS Processing for a Phased Array Study in the NASA Langley Jet Noise Laboratory

Brooks

Humphreys

Plassman

2010

16th AIAA/CEAS Aeroacoustics Conference

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“…Noise source locations, and the effect of jets thereupon, were investigated briefly by the phased-array technique [12]. The data acquisition system consisted of 48 microphones flushmounted to a 1 m x 1 m aluminum plate.…”

Section: Methodsmentioning

confidence: 99%

Effect of Microjet Injection on Supersonic Jet Noise

Zaman

Podboy

2010

16th AIAA/CEAS Aeroacoustics Conference

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The effect of microjet ( jet) injection on the noise from supersonic jets is investigated. Three convergent-divergent (C-D) nozzles and one convergent nozzle, all having the same exit diameters, are used in the study. The jets are injected perpendicular to the primary jet close to the nozzle lip from six equally-spaced ports having a jet-to-primary-jet diameter ratio of 0.0054.Effects in the overexpanded, fully expanded as well as underexpanded flow regimes are explored. Relative to the effect on subsonic jets, larger reductions in the overall sound pressure level (OASPL) are achieved in most supersonic conditions. The largest reductions are typically associated with suppression of screech and transonic tones. For a shock-free, fully expanded case, the OASPL reductions achieved are comparable to that in the subsonic case; the same correlation, found for subsonic jet noise reduction at shallow observation angle, applies.

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“…For broadband noise, of which the acoustic energy is more equally distributed over the mode orders, this may not be the most appropriate approach. This paper proposes a strategy based on deconvolution, using lessons learned from methods that were developed over the past decade for microphone array measurements [13][14][15][16][17][18][19] , and exploiting the fact that the DFT method for azimuthal mode detection is exactly the same as Conventional Beamforming (CB) with microphone arrays 20 . Deconvolution methods start with CB and aim at retrieving source amplitudes using the known CB response of individual sources.…”

Section: Nomenclaturementioning

confidence: 99%

Deconvolution of Azimuthal Mode Detection Measurements

Sijtsma¹,

Brouwer

2017

23rd AIAA/CEAS Aeroacoustics Conference

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Unequally spaced transducer rings make it possible to extend the range of detectable azimuthal modes. The other side of the coin is that the response of the mode detection algorithm to a single mode is distributed over all detectable modes, similarly to the Point Spread Function of Conventional Beamforming with microphone arrays. With multiple modes the response patterns interfere, leading to a relatively high "noise floor" of spurious modes in the detected mode spectrum, in other words, to a low dynamic range. In this paper a deconvolution strategy is proposed for increasing this dynamic range. It starts with separating the measured sound into shaft tones and broadband noise. For broadband noise modes, a standard Non-Negative Least Squares solver appeared to be a perfect deconvolution tool. For shaft tones a Matching Pursuit approach is proposed, taking advantage of the sparsity of dominant modes. The deconvolution methods were applied to mode detection measurements in an AneCom fan rig. An increase in dynamic range of typically 10 to 15 dB was found.

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Improved Phased Array Imaging of a Model Jet

Cited by 56 publications

References 22 publications

DAMAS Processing for a Phased Array Study in the NASA Langley Jet Noise Laboratory

DAMAS Processing for a Phased Array Study in the NASA Langley Jet Noise Laboratory

Effect of Microjet Injection on Supersonic Jet Noise

Deconvolution of Azimuthal Mode Detection Measurements

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