Numerical investigation of nonlinear propagation distortion effects in helicopter rotor noise

Menounou, Penelope; Vitsas, Panagiotis A.

doi:10.1121/1.3203916

Cited by 7 publications

(3 citation statements)

References 17 publications

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“…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. These findings suggest that BWI contours based on average spectra for descent flight conditions can be misleading.…”

Section: Contribution Of Bvi Noise In the Bwi Spectrum Regionmentioning

confidence: 91%

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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Section: Contribution Of Bvi Noise In the Bwi Spectrum Regionmentioning

confidence: 91%

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

Vitsas

Menounou

2012

International Journal of Aeroacoustics

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“…28) can be as high as 7 dB for the affected frequency bands with the octave frequency bands of 1000 and 2000 Hz to be mostly affected. Receiver locations from 1801 to 2201 azimuth angle and from À 401 to À 701 elevation angle seem to be mostly affected [46,47].…”

Section: Nonlinear Propagation Distortion In Blade-vortex Interactionmentioning

confidence: 95%

Aeroacoustics research in Europe: The CEAS-ASC report on 2010 highlights

Nagy

2011

Journal of Sound and Vibration

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“…Menounou and Vitsas [19] used the Burgers equation model to predict nonlinear propagation of helicopter blade-vortex-interaction noise. They assumed that the noise is emitted from the rotor hub center so that r i and r f are measured from the hub center to the starting point and the observer, respectively.…”

Section: Helicopter High-speed Impulsive Noisementioning

confidence: 99%

Improved Algorithm for Nonlinear Sound Propagation with Aircraft and Helicopter Noise Applications

2010

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An efficient numerical method to solve nonlinear sound propagation is presented. The frequency-domain Burgers equation, which includes nonlinear steepening and atmospheric absorption, is formulated in the form of the real and imaginary parts of the pressure. The new formulation effectively eliminates possible numerical issues associated with zero amplitude at higher frequencies occurring in a previous frequency-domain algorithm. In addition, to circumvent a high-frequency error that can occur in the truncated higher frequencies, a split algorithm is developed, in which the Burgers equation is solved below a cutoff frequency and a recursive analytic expression is used beyond the cutoff frequency. Finally, the Lanczos smoothing filter is incorporated to remove the Gibbs phenomenon. The new method is found to successfully eliminate high-frequency numerical oscillations and to provide excellent agreement with the exact solution for an initially sinusoidal signal with only a few harmonics. The new method is applied to a broad range of applications with a comparison to other methods to assess the robustness and numerical efficiency of the method. These include sonic boom, broadband supersonic jet engine noise, and helicopter high-speed impulsive noise. It is shown that the new method provides the fastest and most accurate predictions compared to the other methods for all the application problems. Nomenclature A = amplitude of the Fourier transform pressure, Pa s B n = nth harmonic amplitude c = blade chord length, m c 0 = speed of sound, m s 1 D j = jet exit diameter, m f = frequency of the acoustic signal, Hz f c = cutoff frequency, Hz f 0 = fundamental frequency of the sinusoidal signal, Hz k = wave number, m 1 M = Mach number M a = u a =c 0 , u a is the peak particle velocity at the source, M a p a = 0 c 2 0 m = parameter for plane, cylindrical, and spherical waves n = index of harmonic p = acoustic pressure, Pã p = Fourier transform of the pressure, Pa s p a = initial pressure amplitude of the sinusoidal wave, Pa Q = amplitude of the Fourier transform of the pressure square, Pa 2 s q = acoustic pressure squared, Pa 2 q = Fourier transform of the pressure square, Pa 2 s R = rotor blade radius, m r = propagation distance, m r f = final distance for the sound propagation, m r i = initial or starting distance for the sound propagation, m U = real part of the Fourier transform of the pressure square, Pa 2 s V = imaginary part of the Fourier transform of the pressure square, Pa 2 s X = real part of the Fourier transform of the pressure, Pa s x = shock formation distance, m Y = imaginary part of the Fourier transform of the pressure, Pa s = atmospheric absorption, neper m 1 0 = atmospheric absorption and dispersion, i d , m 1 = coefficient of nonlinearity d = atmospheric dispersion, m 1 = ratio of the specific heats = diffusivity of sound, m 2 s 1 "= nonlinear coefficients, = 0 c 3 0 , kg 1 s 0 = density, kg m 3 = dimensionless propagation distance, x= x = retarded time, s = phase of the Fourier transform of the pressure,...

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Numerical investigation of nonlinear propagation distortion effects in helicopter rotor noise

Cited by 7 publications

References 17 publications

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

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

Aeroacoustics research in Europe: The CEAS-ASC report on 2010 highlights

Improved Algorithm for Nonlinear Sound Propagation with Aircraft and Helicopter Noise Applications

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