Direct Calculation of Sound Radiated From Bodies in Nonuniform Flows

Atassi, Hafiz M.; Fang, J.; Patrick, Sheryl M.

doi:10.1115/1.2910182

Cited by 37 publications

(12 citation statements)

References 6 publications

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“…The effects of aerofoil geometrical parameters, such as angle of attack, aerofoil thickness, camber, etc. on the generation of leading-edge turbulence interaction noise has also been the subject of some theoretical works (Goldstein & Atassi 1976;Goldstein 1978;Myers & Kerschen 1995, 1997Atassi et al 1993;Devenport et al 2010;Roger & Carazo 2010).…”

Section: Introductionmentioning

confidence: 99%

On the noise prediction for serrated leading edges

Lyu

Azarpeyvand

2017

J. Fluid Mech.

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An analytical model is developed for the prediction of noise radiated by an aerofoil with leading edge serration in a subsonic turbulent stream. The model makes use of the Fourier Expansion and Schwarzschild techniques in order to solve a set of coupled differential equations iteratively and express the far-field sound power spectral density in terms of the statistics of incoming turbulent upwash velocity. The model has shown that the primary noise reduction mechanism is due to the destructive interference of the scattered pressure induced by the leading edge serrations. It has also shown that in order to achieve significant sound reduction, the serration must satisfy two geometrical criteria related to the serration sharpness and hydrodynamic properties of the turbulence. A parametric study has been carried out and it is shown that serrations can reduce the overall sound pressure level at most radiation angles, particularly at downstream angles close to the aerofoil surface. The sound directivity results have also shown that the use of leading edge serration does not particularity change the dipolar pattern of the far-field noise at low frequencies, but it changes the cardioid directivity pattern associated with radiation from straight-edge scattering at high frequencies to a tilted dipolar pattern. † Email address for correspondence: bl362@cam.ac.uk arXiv:1706.04509v1 [physics.flu-dyn]

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Section: Introductionmentioning

confidence: 99%

On the noise prediction for serrated leading edges

Lyu

Azarpeyvand

2017

J. Fluid Mech.

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“…where 0(x) is the mean velocity, and the boundary conditions 0 0 (7) (8) along the surface of the body £ and its wake W. The potential function </ > satisfies the equation (9) Numerical solutions using this approach were obtained for a three-dimensional periodic gust in subsonic flow for a single airfoil by Scott and Atassi [15] and [16], and for a two-dimensional cascade geometry by Hall and Verdon [17], Fang and Atassi [18], and Atassi et al [19]. The computation time required for these solutions is less than a minute on scientific workstations.…”

Section: Mean Potential Flowsmentioning

confidence: 97%

Aeroacoustics of nonuniform flows

Atassi

1997

35th Aerospace Sciences Meeting and Exhibit

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“…More complete discussions of the theoretical development are given by Sears, 1 von Kármán and Sears, 3 Atassi, 4 and Atassi et al 5 The equations governing an inviscid, compressible ow past an airfoil at zero angle of attack to a stream with uniform upstream velocity U 1 are the Euler equations. If it is assumed that the unsteady ow component is small, then the upstream ow can be linearized about the mean ow as…”

Section: Theoretical Developmentmentioning

confidence: 99%

Experimental Investigation of Unsteady Aerodynamics and Aeroacoustics of a Thin Airfoil

Minniti

Mueller

1998

AIAA Journal

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An experimental investigation of the unsteady problem for a thin, symmetric airfoil exposed to periodic gusting was performed in a free-jet anechoic wind-tunnel facility. The gusting events were created upstream such that there was a small longitudinal, i.e., spanwise, wave number and the gust could be approximated as two dimensional. Measurements of the unsteady velocity eld, the unsteady pressure at the airfoil surface, and the acoustic eld were made for two values of axial and normal reduced frequency. The unsteady pressure distributionalong the airfoil was computed using the Sears method and unsteady velocity data. In addition, the pressure distribution was computed using acoustic data as input to a numerical inversion technique. The results of each technique were compared with the experimentally obtained unsteady pressure distribution. The inversion technique showed good agreement with the Sears method. However, comparison with experimental results illustrated that the theoretical estimates, although exhibitingtrends similar to the experimental data, consistently underestimated the experimental unsteady pressure distribution at the lower reduced frequency, indicating the presence of viscous effects. Better agreement between experimental and theoretical results was obtained at the higher reduced frequency where viscous effects were less prominent. Nomenclature a = gust velocity vector C p 0 = unsteady pressure coef cient, p 0 =½a 2 U 1 c = airfoil chord f k = single discrete value within the frequency range of spectral analysis f RPF = primary rod passage frequency H .2/ v = vth-order Hankel function of the second kind K = Helmholtz operator k = wave number vector M 1 = freestream Mach number m = harmonic (mode) number P. y/ = acoustic pressure measured at observation location S.k 1 / = Sears function U .t / = axial velocity component U.x; t / = total velocity eld U D = velocity de cit in stationary frame U G = gust velocity vector U m = velocity de cit in wake behind the rod U R = rotational velocity of rod U 0 = relative velocity seen by rotating rod U 1 = freestream velocity vector u.x; t / = unsteady portion of velocity eld u a .x; t / = acoustic portion of unsteady velocity u 1 .x; t / = rotational portion of unsteady velocity V .t / = normal velocity component x = source position vector y = acoustic eld observation position vector 1p 0 .x ¤ 1 ; k ¤ 1 / = unsteady pressure jump on airfoil ½ = density of air ! = gust frequency

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Direct Calculation of Sound Radiated From Bodies in Nonuniform Flows

Cited by 37 publications

References 6 publications

On the noise prediction for serrated leading edges

On the noise prediction for serrated leading edges

Aeroacoustics of nonuniform flows

Experimental Investigation of Unsteady Aerodynamics and Aeroacoustics of a Thin Airfoil

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