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The spectral characteristics of rotor blade-vortex interaction noise - Experimental and mathematical resultsThe BVI impulsive content of a rotor acoustic signal is shown to appear in the mid-frequency range of the power spectrum, between the fifth and thirtieth harmonics of the blade passage frequency, concentrated at the harmonics of the blade passage frequency. These harmonics exhibit a humped or scalloped shape in this mid-frequency spectral region. Increased energy at the harmonics of the shaft frequency appears when the BVI impulsive content demonstrates unsteadiness and blade-to-blade differences in the time domain. A mathematical model of a generalized BVI acoustic signal and its power spectrum shows that the power spectrum is scalloped and filtered by a comb function. The spectrum amplitude is defined by the impulse amplitude and emission time. The scalloping of the spectrum is related to the emission time of the impulse itself, and the spacing of the comb function is related to the repetition time (period) of the impulse. The decay rate of the spectral humps is governed by the inverse of frequency squared. The mathematical model validates the characteristics observed in the data and verify that these characteristics are due to blade-vortex interaction activity.
Document ID
19870035237
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Martin, Ruth M.
(NASA Langley Research Center Hampton, VA, United States)
Hardin, Jay C.
(NASA Langley Research Center Hampton, VA, United States)
Date Acquired
August 13, 2013
Publication Date
January 1, 1987
Subject Category
Acoustics
Report/Patent Number
AIAA PAPER 87-0251
Accession Number
87A22511
Distribution Limits
Public
Copyright
Other

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