DETECTION OF STICK-SLIP OCCURRENCES THROUGH NEAR FIELD NOISE MEASUREMENTS

This paper examines a supersonic multi-jet interaction problem that we believe is likely to be important for mixing enhancement and noise reduction in supersonic mixer-ejector nozzles. We demonstrate that it is possible to synchronize the screech instability of four rectangular jets by precisely adjusting the inter-jet spacing. Our experimental data agree with a theory that assumes that the phase-locking of adjacent jets occurs through a coupling at the jet lip. Although synchronization does not change the frequency of the screech tone, its amplitude is augmented. The synchronized multi- jets exhibit higher spreading than the unsynchronized jets, with the single jet spreading the least. We compare the near-field noise of the four jets with synchronized screech to the noise of the sum of four jets operated individually. Our noise measurements reveal that the more rapid mixing of the synchronized multi-jets causes the peak jet noise source to move upstream and to radiate noise at larger angles to the flow direction. Based on our results, we have grounds to believe that screech synchronization is advantageous for noise reduction internal to a mixer-ejector nozzle, since the noise can now be suppressed by a shorter acoustically lined ejector.

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Visualization of Clear Echocardiographic Images with Near Field Noise Reduction Technique: Experimental Study and Clinical Experience

Journal of the American Society of Echocardiography ◽

10.1016/s0894-7317(98)70043-4 ◽

1998 ◽

Vol 11 (6) ◽

pp. 660-667 ◽

Cited By ~ 7

Author(s):

Takeshi Hozumi ◽

Kiyoshi Yoshida ◽

Yasuhiko Abe ◽

Ryoichi Kanda ◽

Takashi Akasaka ◽

...

Keyword(s):

Experimental Study ◽

Noise Reduction ◽

Clinical Experience ◽

Near Field ◽

Reduction Technique ◽

Field Noise ◽

Echocardiographic Images ◽

Noise Reduction Technique

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A cross-comparison of different post-processing and acoustic measurement devices for high speed near field noise on the S1MA BHCR open rotor test rig

20th AIAA/CEAS Aeroacoustics Conference ◽

10.2514/6.2014-3317 ◽

2014 ◽

Author(s):

Fabien Mery

Keyword(s):

High Speed ◽

Near Field ◽

Acoustic Measurement ◽

Post Processing ◽

Test Rig ◽

Open Rotor ◽

Measurement Devices ◽

Field Noise

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Ground Attenuation Factor Based on Measurements

INTER-NOISE and NOISE-CON Congress and Conference Proceedings ◽

10.3397/in-2021-2405 ◽

2021 ◽

Vol 263 (3) ◽

pp. 3436-3447

Author(s):

Dan Lin ◽

Andrew Eng

Keyword(s):

Near Field ◽

Attenuation Factor ◽

Measurement Data ◽

Low Frequency ◽

Sound Sources ◽

Frequency Sound ◽

Sound Levels ◽

Different Types ◽

Noise Measurements ◽

Field Sound

Assumptions made on the ground types between sound sources and receivers can significantly impact the accuracy of environmental outdoor noise prediction. A guideline is provided in ISO 9613-2 and the value of ground factor ranges from 0 to 1, depending on the coverage of porous ground. For example, a ground absorption factor of 1 is suggested for grass ground covers. However, it is unclear if the suggested values are validated. The purpose of this study is to determine the sound absorption of different types of ground by measurements. Field noise measurements were made using an omnidirectional loudspeaker and two microphones on three different types of ground in a quiet neighborhood. One microphone was located 3ft from the loudspeaker to record near field sound levels in 1/3 and 1 octave bands every second. The other microphone was located a few hundred feet away to record far field sound in the same fashion as the near field microphone. The types of ground tested were concrete, grass, and grass with trees. Based on the measurement data, it was found that grass and trees absorb high frequency sound well and a ground factor of 1 may be used for 500Hz and up when using ISO 9613-2 methodology. However, at lower frequencies (125 Hz octave band and below), grassy ground reflects sound the same as concrete surfaces. Trees absorb more low frequency sound than grass, but less than ISO 9613-2 suggested.

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