Spectral characteristics of rotor blade/vortex interaction noise

Martin, Ruth M.; Hardin, Jay C.

doi:10.2514/3.45542

Cited by 11 publications

(10 citation statements)

References 4 publications

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“…The filtering method was based on previous analytical research that showed BVI noise exists predominantly in the higher frequency range of a signal (Refs. 23,24). This was further confirmed in previous research, where it was shown that BVI noise is quite energetic relative to the overall pressure signal, when such noise is present (Ref.…”

Section: Discussionsupporting

confidence: 83%

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Extracting Blade–Vortex Interactions Using Continuous Wavelet Transforms

Stephenson¹,

Tinney²

2017

j am helicopter soc

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A framework for using continuous wavelet transforms to isolate and extract blade-vortex interaction noise from helicopter acoustic signals is described. The extraction method allows for the investigation of blade-vortex interactions independent of other sound sources. Experimentally acquired acoustic data from full-scale helicopter flyover tests are first transformed into time-frequency space through the wavelet transformation, with blade-vortex interactions identified and filtered by their high-amplitude, high-frequency impulsive content. The filtered wavelet coefficients are then used to create a pressure signal solely related to blade-vortex interactions. Analysis of a synthetic data set is conducted and shows that blade-vortex interactions can be accurately extracted so long as the blade-vortex interaction wavelet energy is comparable to the wavelet energy in the main rotor harmonic.

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Section: Discussionsupporting

confidence: 83%

“…The tail rotor noise signal is primarily identified in the midrange frequency, whereas the BVI noise signals are identified by their higher harmonics (Refs. 3,6,23,24).…”

Section: Blade-vortex Interaction Extraction Methodsmentioning

confidence: 99%

Extracting Blade–Vortex Interactions Using Continuous Wavelet Transforms

Stephenson¹,

Tinney²

2017

j am helicopter soc

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“…It can be observed that the frequency content of the BWI region [ Figure 9(b)], almost in its entire range, is arranged in equally spaced peaks, which also form some greater humps. These characteristics, which are seen over a large number of microphones in the advancing side region, reveal that the effect of BVI impulsive noise in the BWI frequency region is dominant [25]. Moreover, Menounou and Vitsas [26] have shown that nonlinear effects, which steepen BVI pulses with propagation distance, can transfer their energy to higher frequencies beyond the traditional BVI range and into BWI range.…”

Section: Contribution Of Bvi Noise In the Bwi Spectrum Regionmentioning

confidence: 92%

Analysis of the Helishape Descent Database with Regards to Blade-Wake Interaction Noise

Vitsas

Menounou

2012

International Journal of Aeroacoustics

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Helicopter rotor Blade Wake Interaction (BWI) noise is known to be significant during takeoff and level flight. Less attention has been given to descent flight conditions, where Blade Vortex Interaction (BVI) noise is dominant. The present study investigates BWI noise in descent flight conditions by analyzing the HELISHAPE descent case database. Through signal analysis of both acoustic waveforms and spectra, the rotor azimuthal region responsible for BWI noise is localized and the dominance of BVI noise in the BWI frequency region is shown. Coherence analysis of the blade pressure data indicate significant chordwise coherence in the 3 to 4 Strouhal number range and absence of acoustic dipoles in the BWI frequency range. Comparison with analysis of a swept-back blade-tip database showed that blade-tip shape does not affect BWI noise. The findings of this study support BWI prediction models based on Amiet's theory and suggest that BWI noise can be ignored for predictions of rotor noise in descent flight conditions.

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“…23 For the purposes of the present study, the rise time seems to be a more appropriate parameter. Consider a BVI signal idealized as a train of N-shaped pulses with DT Ͻ T / 2.…”

Section: B Effect Of Impulsiveness Of Advancing Side Bvi Noise-weighmentioning

confidence: 98%

Numerical investigation of nonlinear propagation distortion effects in helicopter rotor noise

Menounou

Vitsas

2009

The Journal of the Acoustical Society of America

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The effect of nonlinear propagation distortion on helicopter rotor noise is presented based on measured data for low-speed descent and numerical calculations that predict the noise level away from the helicopter with and without nonlinear effects. It is shown that for some frequency bands the difference between linear and nonlinear calculations can be as high as 7 dB. Blade vortex interaction (BVI) noise, the dominant noise contributor during descent, is mainly examined. It is shown that advancing side BVI noise is affected by nonlinear distortion, while retreating side BVI noise is not. Based on signal characteristics at source, two quantities are derived. The first quantity (termed polarity) is based on the pressure gradient of the source signal and can be used to determine whether a BVI signal will evolve as an advancing or a retreating side signal. The second quantity (termed weighted rise time) is a measure of the impulsiveness of the BVI signal and can be used to determine at which frequency nonlinear effects start to appear. Finally, polarity and weighted rise time are shown to be applicable in cases of BVI noise generated from different blade tips, as well as in cases of non-BVI noise.

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Spectral characteristics of rotor blade/vortex interaction noise

Cited by 11 publications

References 4 publications

Extracting Blade–Vortex Interactions Using Continuous Wavelet Transforms

Extracting Blade–Vortex Interactions Using Continuous Wavelet Transforms

Analysis of the Helishape Descent Database with Regards to Blade-Wake Interaction Noise

Numerical investigation of nonlinear propagation distortion effects in helicopter rotor noise

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