Helicopter Noise: State-of-the-Art

George, A. R.

doi:10.2514/3.58436

Cited by 82 publications

(13 citation statements)

References 47 publications

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“…1 Of these complex rotor flow problems, blade-vortex interaction has been an important research subject in fundamental rotor aerodynamics since it was identified as a helicopter impulsive noise source in addition to the high advancing blade Mach number. 2 occur when the helicopter is in powered descending motion. 3 To date, the acoustic formulation of the blade-vortex interaction noise has been well developed; however, the complex aerodynamic data for the input to the acoustic formulation are not provided sufficiently.…”

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confidence: 99%

Investigation of the parallel blade-vortex interaction at low speed

Seath

Kim

Wilson³

1989

Journal of Aircraft

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Low-speed wind-tunnel tests were conducted to investigate the parallel blade-vortex interaction. Flowvisualization tests of vortex generation performed before the pressure tests showed that a well-defined starting vortex was generated by an impulsively pitched wing. Time history of the pressure distribution on a pressuretapped wing model was acquired as the starting vortex passed over the wing. These pressure tests revealed that a substantial pressure change near the leading edge was induced by the encountering vortex. The effects of vortex proximity, reduced frequency, and maximum pitch angle of the vortex generator on the pressure change were also investigated. Nomenclature c = chord length of instrument wing c vg = chord length of vortex generator wing Q = section lift coefficient of instrumented wing C p = pressure coefficient of instrumented wing, (P-P*)/q k = reduced frequency, ctc vg / VP -local static pressure P ini = initial local static pressurê max = maximum local static pressurê min = minimum local static pressure Pa, = freestream static pressure q = freestream dynamic pressure Re = Reynolds number T = time elapsed after vortex generation V w = freestream velocity x = longitudinal distance from instrumented wing leading edge to pressure tap x v = longitudinal distance from instrumented wing leading edge to vortex center y v = vortex generator height above wing a. = pitch angle of vortex generator «max = maximum pitch angle of vortex generator a = pitch rate of vortex generator fi m = freestream viscosity F = vortex strength Po, = freestream density

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mentioning

confidence: 99%

Investigation of the parallel blade-vortex interaction at low speed

Seath

Kim

Wilson³

1989

Journal of Aircraft

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“…The list of possible rotor noise mechanisms is lengthy but in the absence of impulsive noise, broadband noise can be an important contribution. 2 ' 3 Design of helicopters with reduced broadband noise level requires the ability to predict the contribution from each broadband noise mechanism.…”

Section: Tmentioning

confidence: 99%

Rotor noise due to atmospheric turbulence ingestion. I - Fluid mechanics

Simonich¹,

Amiet²,

Schlinker³

et al. 1990

Journal of Aircraft

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An analysis has been developed to predict helicopter rotor noise due to ingestion of turbulence. The method incorporates an upstream isotropic turbulence model and a (rapid distortion) turbulence contraction description to determine the statistics of the anisotropic turbulence at the rotor plane. Ah important feature of the contraction process is the differential drift of fluid particles on adjacent streamlines, which leads to tipping and stretching of the vortex filaments associated with the turbulence. The analysis is applied to a main rotor operating in atmospheric turbulence. For mean-flow contraction ratios representative of hover and low-speed forward flight and vertical ascent, computations are carried out to show that accurate prediction of the vorticity components and hence nonisotropic turbulence at the rotor face requires accounting for this differential drift. A companion paper, 1 presented as Part II, describes the rotor acoustic model and the resulting atmospheric turbulence ingestion noise prediction based on the method. Although the predictions in both papers are limited to atmospheric turbulence, the method is applicable to isotropic upstream turbulence fields undergoing generalized distortions. NomenclatureC T = rotor thrust coefficient = T/picR 2 (QR ) 2 e -unit vector along one of the three upstream or downstream axes E(k) = wave-number energy spectrum g = gravitational acceleration k -wave number k = wave vector of turbulence L £ = integral length scale n = direction of the principle normal to the streamline q,Q = velocity field and magnitude of a Fourier component of turbulence R = rotor radius T = thrust u -turbulence fluctuation U = local time mean velocity C/oo = mean horizontal freestream velocity FOO = mean vertical freestream velocity .___ VQ = rotor-induced velocity = C T QR /2V\ 2 + /x 2 v___ = vertical turbulence fluctuations Vt^/C/oo = rms turbulence intensity x t = upstream Cartesian coordinate system, / = 1,2,3 X = vector location Z = height above ground a = rotor tip path plane angle of attack eyk = alternating tensor X = wavelength of Fourier component of turbulence, or rotor inflow ratio = (£/« sina-= rotor advance ratio = U^ cosa/(tiR) = downstream Cartesian coordinate system = density = wake skew angle = tan" 1 x [-I/. cosa/(£/oo sine*-V Q )\ = rotation rate = vorticity field and magnitude of a Fourier component of turbulence [see Eq. (6)] ij f k = specify either a vector (such as one of the vectors £1, ^2, £3) or a 1 , 2, 3 component of a vector (such as the first Cartesian component of the vector e 2 ) Superscripts U,D = upstream or downstream location, respectively

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“…Over the past few years, with the development of the civil aviation industry, helicopters have been used extensively in low-level operations. With the increasingly stringent airworthiness standards of aviation authorities around the world, how to reduce noise pollution has become an important consideration in the design of helicopters [1]. There are three main sources of noise in helicopter operations: rotor noise, engine noise, and transmission system noise [2][3][4][5].…”

Section: Introductionmentioning

confidence: 99%

Aerodynamic and Aeroacoustic Performance of Tail Rotor Investigation and Modification

Hao¹,

Jia²

2021

Preprint

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With the increasingly stringent airworthiness standards, the noise generated during the rotorcraft flight is gradually attracting people’s attention. It widely operated helicopters at low altitudes because of their maneuverability. The way to reduce the noise caused by the complex airflow of the helicopter rotor system has progressively become a hot topic for researchers. Using a hybrid acoustic analysis method, this paper investigates the improvement of the noise and thrust of the helicopter’s tail rotor through the tail rotor structural parameters. For the basic model, the turbulence simulation is performed using an incompressible detached eddy simulation (DES) method, and the Lighthill acoustic analog equation is calculated using the finite element method (FEM). We verified the accuracy of the method through wind tunnel tests. We chose a series of structural parameters for sound simulation and fluid simulation calculations. The results indicate that the modified tail rotor noise reduced by 16.5 dBA and the total thrust increased by 19.9% from the prototype model. This work can enhance the duct tail rotor design to improve aerodynamic and aeroacoustic performance.

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Helicopter Noise: State-of-the-Art

Cited by 82 publications

References 47 publications

Investigation of the parallel blade-vortex interaction at low speed

Investigation of the parallel blade-vortex interaction at low speed

Rotor noise due to atmospheric turbulence ingestion. I - Fluid mechanics

Aerodynamic and Aeroacoustic Performance of Tail Rotor Investigation and Modification

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