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Journal of the Acoustical Society of America

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Mar 2010

Volume 127, Issue 3, pp. EL87-2044

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Detecting blast-induced infrasound in wind noise

Wheeler B. Howard, Kevin L. Dillion, and F. Douglas Shields

J. Acoust. Soc. Am. Volume 127, Issue 3, pp. 1244-1250 (2010); (7 pages)

Online Publication Date: 23 Mar 2010

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Current efforts seek to monitor and investigate such naturally occurring events as volcanic eruptions, hurricanes, bolides entering the atmosphere, earthquakes, and tsunamis by the infrasound they generate. Often, detection of the infrasound signal is limited by the masking effect of wind noise. This paper describes the use of a distributed array to detect infrasound signals from four atmospheric detonations at White Sands Missile Range in New Mexico, USA in 2006. Three of the blasts occurred during times of low wind noise and were easily observed with array processing techniques. One blast was obscured by high wind conditions. The results of signal processing are presented that allowed localization of the blast-induced signals in the presence of wind noise in the array response.
Show PACS
43.28.Dm Infrasound and acoustic-gravity waves
43.28.Mw Shock and blast waves, sonic boom
43.60.Gk Space-time signal processing, other than matched field processing

A multi-mode screech frequency prediction formula for circular supersonic jets

J. H. Gao and X. D. Li

J. Acoust. Soc. Am. Volume 127, Issue 3, pp. 1251-1257 (2010); (7 pages)

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A time evolution analysis is presented for the interaction between the instability waves, shock cells, and screech tones based on the authors’ previous numerical simulation database. An attachment and reinforcement process of the upstream propagating screech waves with the downstream hydrodynamic waves is identified and recognized as part of the screech loop. The first five shock cells are recognized as the effective sound source region. Through an analysis of the phase variation in the dominant pressure fluctuations for several typical Mach number screeching jets, it is found that the total number of the instability waves and the upstream feedback sound waves in the effective source region can be identified as 5 for the A1, B, and D modes and 6 for A2 and C modes, respectively. A screech tone frequency prediction formula is thus proposed based on this relation. The predicted screech wavelengths or Strouhal numbers of cold and hot jets all agree well with the experimental data by other researchers, except for a small discrepancy for the B mode. It is also noticed that the measured two A0 modes by Ponton et al. [NASA Technical Memorandum No. 113137, Langley Research Center (1997) ] can be classified to A1 and A2 modes, respectively, according to the proposed formula.
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43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence
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