Helicopter impulsive noise: Theoretical and experimental status

Schmitz, Fredric H.; Yu, Yong

doi:10.1016/s0022-460x(86)80378-9

Cited by 75 publications

(46 citation statements)

References 13 publications

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“…The first theory of aerodynamic noise applies equally [18][19][20][21][22][23] well to the to thickness (monopole), loading (dipole) and turbulence (quadrupole) noise of aircraft propellers [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] (Section 2.1.1), helicopter rotors [41][42][43][44][45][46][47][48][49][50][51][52][53][54][55] (Section 2.1.2) and turbomachinery [56][57][58][59][60][61] requiring that the aerodynamic problem be solved first to specify the sources. The blade-vortex interaction noise (BVI) involves sound radiation by noise sources convected in a non-uniform flow, that does not match so well the assumptions of the first theory of aerodynamic sound of an unbounded medium at rest or in uniform motion with static or moving sources.…”

Section: Helicopter Rotor Noisementioning

confidence: 99%

On Physical Aeroacoustics with Some Implications for Low-Noise Aircraft Design and Airport Operations

Campos

2015

Aerospace

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Air traffic is growing at a steady rate of 3% to 5% per year in most regions of the world, implying a doubling every 15-25 years. This requires major advances in aircraft noise reduction at airports, just not to increase the noise exposure due to the larger number of aircraft movements. In fact it can be expected, as a consequence of increased opposition to noise by near airport residents, that the overall noise exposure will have to be reduced, by bans, curfews, fines, and other means and limitations, unless significantly quieter aircraft operations are achieved. The ultimate solution is aircraft operations inaudible outside the airport perimeter, or noise levels below road traffic and other existing local noise sources. These substantial noise reductions cannot come at the expense of a degradation of cruise efficiency, that would affect not just economics and travel time, but would increase fuel consumption and emission of pollutants on a global scale. The paper reviews the: (i) current knowledge of the aircraft noise sources; (ii) the sound propagation in the atmosphere and ground effects that determine the noise annoyance of near-airport residents; (iii) the noise mitigation measures that can be applied to current and future aircraft; (iv) the prospects of evolutionary and novel aircraft designs towards quieter aircraft in the near term and eventually to operations inaudible outside the airport perimeter. The 20 figures and 1 diagram with their legends provide a visual summary of the review.

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Section: Helicopter Rotor Noisementioning

confidence: 99%

On Physical Aeroacoustics with Some Implications for Low-Noise Aircraft Design and Airport Operations

Campos

2015

Aerospace

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“…These transonic effects can result in the formation of a shock on the blade surface, which can extend past the tip of the blade and into the far-field (also known as "delocalization") 4,5 . However, tail rotors are often designed to operate at tip Mach numbers and aspect ratios low enough to avoid HSI 6,7,8 and other compressibility related effects.…”

Section: Tail Rotor Noisementioning

confidence: 99%

In-Flight Array Measurements of Tail Rotor Harmonic Noise

Sargent¹,

Schmitz²,

Sim³

2010

j am helicopter soc

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Acoustic data that utilized a unique flying microphone boom array was analyzed using a time domain averaging technique, based on a theoretical tail rotor one-per-rev signal, to obtain tail rotor acoustic time histories for forward and descending flight. This flying microphone array approach provides useful insight into the directivity and noise mechanisms associated with the periodic harmonic noise generated by the Bell 206B tail rotor. Comparisons between linear harmonic noise theory and the time averaged data show good agreement, indicating that the average harmonic noise of the 206B is dominated by thickness noise near the tip-path-plane of the tail rotor and by loading noise at the out-of-plane microphone positions. The measured data also provides trends in the overall sound pressure level (OASPL) with respect to both forward velocity and descent angle. A significant deviation from the average SPL of the harmonic noise levels at high frequencies is also shown.

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“…Boxwell [9,8,68] consists of a fixed wing aircraft flying in formation with the helicopter being tested ( Fig. 1.11).…”

Section: Experimental Approachesmentioning

confidence: 99%

“…Since the "delocalized" 7 shock wave tends to radiate in-plane, this sound source is mostly focused in and slightly below the plane of the rotor and is particularly important for military detection. In the recent past, several flight tests [8] and pioneering experiments conducted in wind tunnels and hover chambers [6,7,9] have been conducted to characterize and understand this particular source. Some of the solutions including lower rotor tip speeds and/or innovative blade designs, like the BERP tip [10] have been incorporated in modern helicopters.…”

mentioning

confidence: 99%

A New Experimental Approach to Study Helicopter Blade-Vortex Interaction Noise

Koushik

2008

14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference)

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A unique and novel experimental approach has been developed to study the aerodynamics and acoustics of the helicopter Blade-Vortex Interaction in a controlled hover environment. This is achieved by having a non-lifting single-bladed rotor with a rigid hub interact with a carefully controlled gust disturbance that replicates the essential characteristics of the vortex velocity. This experimental approach termed the Blade-Controlled Disturbance-Interaction or the BCDI, decouples the rotor parameters from the charactersitics of the incident disturbance velocity, thus providing an ideal setup for studying the blade's aerodynamics and acoustic response in detail. Moreover, the angle of interaction between the disturbance field and the rotor blade can be controlled by orienting the gust, providing the ability to study both parallel and oblique interactions. The noise data was recorded at thirty different microphone locations.A series of experiments at various rotor tip Mach numbers and interaction angles, replicating many of the conditions of helicopter BVI, were performed. The results show that the the directionality of the BVI noise is strongly determined by the interaction angle. A small change in interaction angle results in the radiation of noise over a larger azimuthal area compared to the parallel interaction. Moreover, as the interaction becomes more oblique, the peak noise elevation angle approaches closer to the rotor plane.A linear unsteady lifting-line aerodynamic theory (corrected for chord-wise non-compactness )was used to estimate the blade aerodynamics during the interaction and hence the radiated noise.Although the theory under-predicted the noise levels for most of the cases, and did not replicate exactly the general pulse shape, the general directionality trends were predicted reasonably well.The theory was used to separate the contribution to the acoustics, from different spanwise blade sections, providing significant insights into the phasing mechanism of BVI noise.

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Helicopter impulsive noise: Theoretical and experimental status

Cited by 75 publications

References 13 publications

On Physical Aeroacoustics with Some Implications for Low-Noise Aircraft Design and Airport Operations

On Physical Aeroacoustics with Some Implications for Low-Noise Aircraft Design and Airport Operations

In-Flight Array Measurements of Tail Rotor Harmonic Noise

A New Experimental Approach to Study Helicopter Blade-Vortex Interaction Noise

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