W. Davis et al., EXTRACTING AND CHARACTERIZING BLADE-VORTEX INTERACTION NOISE WITH WAVELETS, Journal of the American Helicopter Society, 42(3), 1997, pp. 264-271
Applications of a discrete implementation of tile wavelet transform (W
T) to the analysis of blade-vortex interaction (BVI) noise are present
ed, The method decomposes a signal into a series of orthogonal subband
s logarithmically spaced in frequency while simultaneously preserving
temporal information, A BVI detection algorithm was developed which ta
kes advantage of the prominence of BVI noise in certain subbands, A me
thod for extracting BVI noise from other noise sources is described. T
hree metrics are tested for suitability as BVI estimators. One of thes
e, a root-mean square (RMS) metric, characterizes BVI noise severity,
hut requires the added computational effort of inverting the transform
, The other two metrics are computed using the information available f
rom the WT. The first of these, computed from the amplitudes of BVI ev
ents in a single subband, correlates with peak-to-peak pressure and is
relatively insensitive to noise, The second of these, based on the ex
ponential behavior of peak amplitudes across subbands, is apparently u
nable to characterize BVI noise severity and is highly sensitive to no
ise.