A note on the tip noise of rotating blades

Farassat, F.; Martin, Ruth M.

doi:10.1016/0022-460x(83)90589-8

Cited by 12 publications

(4 citation statements)

References 6 publications

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“…where the term on the left side of equation ( 24) is recognized as the thickness source term in equation ( 19) and the term on the right side of equation ( 24) is the loading source term of equation ( 19) with with a constant pressure jump p − p o = ρ o c 2 . Although mathematically equivalent, the two formulations for thickness noise have quite different characteristics and robustness when integrated numerically [38]. More examples of the nonuniqueness of the source description are given by Ffowcs Williams [39] and Kanwal [32].…”

Section: Interpretation and Observationsmentioning

confidence: 99%

Modeling aerodynamically generated sound of helicopter rotors

Brentner

Farassat

2003

Progress in Aerospace Sciences

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416

209

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A great deal of progress has been made in the modeling of aerodynamically generated sound of rotors over the past decade. Although the modeling effort has focused on helicopter main rotors, the theory is generally valid for a wide range of rotor configurations. The Ffowcs Williams-Hawkings (FW-H) equation has been the foundation for much of the development. The monopole and dipole source terms of the FW-H equation account for the thickness and loading noise, respectively. Bladevortex-interaction noise and broadband noise are important types of loading noise, hence much research has been directed toward the accurate modeling of these noise mechanisms. Both subsonic and supersonic quadrupole noise formulations have been developed for the prediction of high-speed impulsive noise. In an effort to eliminate the need to compute the quadrupole contribution, the FW-H equation has also been utilized on permeable surfaces surrounding all physical noise sources. Comparisons of the Kirchhoff formulation for moving surfaces with the FW-H equation have shown that the Kirchhoff formulation for moving surfaces can give erroneous results for aeroacoustic problems. Finally, significant progress has been made incorporating the rotor noise models into full vehicle noise prediction tools.

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Section: Interpretation and Observationsmentioning

confidence: 99%

Modeling aerodynamically generated sound of helicopter rotors

Brentner

Farassat

2003

Progress in Aerospace Sciences

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416

209

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“…Nearly 30 chordwise divisions and 75 equally spaced spanwise divisions are needed for the computation to converge completely for this test case. After applying the consistency test, it is shown that in the numerical study, the calculated Isom noise and the monopole noise do not agree exactly in amplitude as already noticed by Farassat [16,17,18], (See Figure 13). Theoretically, the sources on the airfoil-shaped cut at the very tip and the inner radius of the blade, which were neglected in the previous calculations, must be included in noise prediction (See Figure 14).…”

Section: Tc4: Isom Thickness Noisementioning

confidence: 66%

Validation of a Time Domain Formulation for Propeller Noise Prediction

Ghorbaniasl

Hirsch

2006

International Journal of Aeroacoustics

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The present paper is oriented at the definition of a series of validation test cases for the far-field subsonic formulation of Farassat in the time domain, solving the Lighthill analogy for aeroacoustics in the Ffowcs William-Hawkings formulation for far-field noise predictions. The focus will be on the definition, validation and verification of four test cases for far-field acoustic propagation. The test cases are: (i) a rotating rotor with a pre-defined body force, (ii) a translating and rotating small disk case with a moving observer, (iii) a conventional helicopter rotor case, (iv) and the consistency test known as the Isom thickness noise. The acoustic pressure signature, sound pressure level and directivity have been calculated for each test case. Graphical outputs and comparisons of results with those of analytical solutions are presented.

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“…Aspects of helicopter rotor noise of particular interest include blade and tip noise [38,39,40] and blade vortex interaction (BVI) noise [41]; the latter accounts for the characteristic slapping noise of helicopters [42], heard by the human ear and recorded in experiments [33,43]. The helicopter rotor noise consists of discrete tones [44,45,46] plus a continuous broadband [47].…”

Section: Introductionmentioning

confidence: 99%

On a Generalized Multipole Expansion with Application to Propeller Design Synthesis

Campos

Lau

2014

International Journal of Aeroacoustics

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The radiation of sound by surfaces in motion in a non-uniform flow, including the effects of reflections from obstacles on noise, is specified by an extension of the Kirchhoff integral that leads to a generalized multipole expansion that extends the classical series of spherical harmonics to account for the effects of (i) the moving medium and (ii) the rotating sound sources. The corresponding radiation integrals are evaluated analytically for an arbitrary source distribution along the blades of a propeller at an angular inflow. The effects of the incident flow and propeller rotation on the amplitude and phase of sound, e.g. through the retarded time, lead to an extension of the generating function for Legendre polynomials; this provides the representation of the acoustic field as the generalized multipolar series. Each generalized multipole sound field is shown to consist of a fundamental blade passng frequency (BPF) plus all harmonics, with directivities specified by integrals of Bessel functions, that are evaluated analytically. The theory is validated by comparison with noise measurements using two different model propellers in two distinct aeroacoustic wind tunnels. The experimental results are used to illustrate the principle of propeller noise synthesis, relating the radiated sound field to the sound source distribution.

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A note on the tip noise of rotating blades

Cited by 12 publications

References 6 publications

Modeling aerodynamically generated sound of helicopter rotors

Modeling aerodynamically generated sound of helicopter rotors

Validation of a Time Domain Formulation for Propeller Noise Prediction

On a Generalized Multipole Expansion with Application to Propeller Design Synthesis

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