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Acoustic properties of supersonic helium/air jets at low Reynolds numbersExperiments have been performed with the objective of developing a greater understanding of the physics of hot supersonic jet noise. Cold helium/air jets are used to easily and inexpensively simulate the low densities of hot air jets. The experiments are conducted at low Reynolds numbers in order to facilitate study of the large-scale turbulent structures (instability waves) that cause most of the radiated noise. Experiments have been performed on Mach 1.5 and 2.1 jets of pure air, pure helium and 10 percent helium by mass. Helium/air jets are shown to radiate more noise than pure air jets due to the increased exit velocity. Microphone spectra are usually dominated by a single spectral component at a predictable frequency. Increasing the jet's helium concentration is shown to increase the dominant frequency. The helium concentration in the test chamber is determined by calculating the speed of sound from the measured phase difference between two microphone signals. Bleeding outside air into the test chamber controls the accumulation of helium so that the hot jet simulation remains valid. The measured variation in the peak radiated noise frequency is in good agreement with the predictions of the hot jet noise theory of Tam et al.
Document ID
19930035163
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Mclaughlin, Dennis K.
(NASA Langley Research Center Hampton, VA, United States)
Barron, W. D.
(NASA Langley Research Center Hampton, VA, United States)
Vaddempudi, Appa R.
(Pennsylvania State Univ. University Park, United States)
Date Acquired
August 15, 2013
Publication Date
January 1, 1992
Publication Information
Publication: In: DGLR(AIAA Aeroacoustics Conference, 14th, Aachen, Germany, May 11-14, 1992, Proceedings. Vol. 1 (A93-19126 05-71)
Publisher: Deutsche Gesellschaft fuer Luft- und Raumfahrt
Subject Category
Acoustics
Accession Number
93A19160
Funding Number(s)
CONTRACT_GRANT: NAG1-1047
Distribution Limits
Public
Copyright
Other

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