Computation of Helicopter Rotor Acoustics in Forward Flight

Strawn, Roger C.; Biswas, Rupak

doi:10.4050/jahs.40.66

Cited by 19 publications

(11 citation statements)

References 13 publications

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“…Many applications of the FW-H and Kirchhoff methods can be found in the area of rotorcraft acoustics. [4][5][6][7] The FW-H method has typically been applied AIAA-2002AIAA- -2580 by having the integration surface coincide with solid bodies, but the method is still applicable when the surface is off the body and permeable. The codes developed in this work are valid for both cases.…”

Section: Introductionmentioning

confidence: 99%

A Comparison of Ffowcs Williams-Hawkings Solvers for Airframe Noise Applications

Lockard

2002

8th AIAA/CEAS Aeroacoustics Conference &Amp;amp; Exhibit

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Section: Introductionmentioning

confidence: 99%

A Comparison of Ffowcs Williams-Hawkings Solvers for Airframe Noise Applications

Lockard

2002

8th AIAA/CEAS Aeroacoustics Conference &Amp;amp; Exhibit

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“…A non-rotating formulation uses a nonrotating control surface that encloses the entire rotor (e.g. Forsyth and Korkan, 79 Strawn and Biswas, 80 Baeder et al 81 ). A rotating Kirchhoff formulation allows the control surface to rotate with the blade aligning with the CFD lines, e.g.…”

Section: Rotating or Nonrotating Control Surfacementioning

confidence: 99%

Surface Integral Methods in Computational Aeroacoustics—From the (CFD) Near-Field to the (Acoustic) Far-Field

Lyrintzis¹

2003

International Journal of Aeroacoustics

237

124

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A review of recent advances in the use of surface integral methods in Computational AeroAcoustics (CAA) for the extension of near-field CFD results to the acoustic far-field is given. These integral formulations (i.e. Kirchhoff's method, permeable (porous) surface Ffowcs-Williams Hawkings (FW-H) equation) allow the radiating sound to be evaluated based on quantities on an arbitrary control surface if the wave equation is assumed outside. Thus only surface integrals are needed for the calculation of the far-field sound, instead of the volume integrals required by the traditional acoustic analogy method (i.e. Lighthill, rigid body FW-H equation). A numerical CFD method is used for the evaluation of the flow-field solution in the near field and thus on the control surface. Diffusion and dispersion errors associated with wave propagation in the far-field are avoided. The surface integrals and the first derivatives needed can be easily evaluated from the near-field CFD data. Both methods can be extended in order to include refraction effects outside the control surface. The methods have been applied to helicopter noise, jet noise, propeller noise, ducted fan noise, etc. A simple set of portable Kirchhoff/FW-H subroutines can be developed to calculate the far-field noise from inputs supplied by any aerodynamic near/mid-field CFD code.

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“…We have @ @ (V r) = ?! 2 @ @ + V r @ @ (11) where @=@ is the directional derivative in the (radial direction) and = j j. We also have…”

Section: Formulation and Solution Of The Problemmentioning

confidence: 99%

“…The cause of this noise has been identi ed since the late 1970's 1, 2] as the deterministic quadrupoles in the vicinity of the rotor, and, in the case of delocalization, beyond the sonic circle and the blade tip. Many schemes have been proposed by researchers based on the acoustic analogy 3{9] and the Kirchho method 10,11]. At present, most of these schemes are limited to subsonic quadrupole source motion, however, very recently several methods have been proposed for the prediction of noise from supersonic sonic sources 12{15].…”

Section: Introductionmentioning

confidence: 99%

Supersonic Quadrupole Noise Theory for High-Speed Helicopter Rotors

Farassat

Kenneth

1998

Journal of Sound and Vibration

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High-speed helicopter rotor impulsive noise prediction is an important problem of aeroacoustics. The deterministic quadrupoles have been shown to contribute significantly to high-speed impulsive (HSI) noise of rotors, particularly when the phenomenon of delocalization occurs. At high rotor-tip speeds, some of the quadrupole sources lie outside the sonic circle and move at supersonic speed. Brentner has given a formulation suitable for efficient prediction of quadrupole noise inside the sonic circle. In this paper, a simple formulation is presented based on the acoustic analogy that is valid for both subsonic and supersonic quadrupole noise prediction. Like the formulation of Brentner, the model is exact for an observer in the far field and in the rotor plane, and is approximate elsewhere. The full analytic derivation of this formulation is given in this paper. The method of implementation on a computer for supersonic quadrupoles using marching cubes for constructing the influence surface (S-surface) of an observer space-time variable (x, t) is presented. Then, several examples of noise prediction are given for both subsonic and supersonic quadrupoles. It is shown that in the case of transonic flow over rotor blades, the inclusion of the supersonic quadrupoles improves the prediction of the acoustic pressure signature. The equivalence is shown of the new formulation to that of Brentner for subsonic quadrupoles. It is shown that the regions of high quadrupole source strength are primarily produced by the shock surface and the flow over the leading edge of the rotor. The primary role of the supersonic quadrupoles is to increase the width of a strong acoustic signal.

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Computation of Helicopter Rotor Acoustics in Forward Flight

Cited by 19 publications

References 13 publications

A Comparison of Ffowcs Williams-Hawkings Solvers for Airframe Noise Applications

A Comparison of Ffowcs Williams-Hawkings Solvers for Airframe Noise Applications

Surface Integral Methods in Computational Aeroacoustics—From the (CFD) Near-Field to the (Acoustic) Far-Field

Supersonic Quadrupole Noise Theory for High-Speed Helicopter Rotors

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