An iterative method for predicting turbofan inlet acoustics

Horowitz, S. J.; Sigman, R. K.; Zinn, B. T.

doi:10.2514/3.8006

Cited by 10 publications

(4 citation statements)

References 16 publications

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“…In the non-resonant case k l ≠ k lmn , the inversion of (47) specifies the coefficients D lmn in (41), so that 48is the acoustic field forced by the source distribution (42,43). Solving (35) for the eigenvalues of the radial wavenumber leads to (49) comparing with (5), it follows that (50) that can be simplified:…”

Section: Wave Field Due To Initial Conditions or Sourcesmentioning

confidence: 99%

“…In this case the natural frequencies (37) are real and so are the amplitudes of the forced motion. In the case of impedance walls, uniform or not, the radial wavenumbers (49) are generally complex (21) as well as the natural frequencies (35). In this case resonances can occur for real excitation frequency ω only for modes with real frequency ω lmn that is: (i) exceptionally for impedance walls; (ii) for rigid walls at a natural frequency (37) corresponding to (55d).…”

Section: L'hôpital Rule For Simple or Multiple Resonancementioning

confidence: 99%

“…Recently, multiple scales methods have been used to find solutions valid for duct with slowly varying cross-section and liner acoustic impedance [40,41], and methods based on geometric acoustics have also been applied [42][43][44][45][46]. Acoustic liners have been extensively used as a mean to reduce noise radiated from jet engine exhausts [47,48] and inlets [49,50]. The quest for more effective sound absorption mechanisms in cylindrical ducts has led to the consideration of non-uniform liners, with impedance varying circumferentially [34,[51][52][53][54], or axially or in both directions [55].…”

Section: Introductionmentioning

confidence: 99%

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On Sound Generation in Cylindrical Flow Ducts with Non-Uniform Wall Impedance

Campos

Oliveira

2013

International Journal of Aeroacoustics

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The use of acoustic liners is a common means of noise reduction in jet engine exhausts. The quest for more effective sound absorption mechanisms in cylindrical ducts has led to the consideration of non-uniform liners, with impedance varying circumferentially, axially, or in both directions. The present paper is based on the theory of mode coupling in a non-uniformly lined cylindrical duct and considers the complementary problem of generation of sound or excitation of coupled modes by a source distribution. The sound field due to an arbitrary source distribution is obtained as a superposition of eigenfunctions corresponding to complex eigenvalues for the radial wavenumbers and natural frequencies taking into account that the radial, axial and azimuthal modes are coupled by the non-uniform wall impedance, and including resonant and non-resonant cases. The waveforms are illustrated for point monopole, dipole and quadrupole sources and a continuous monopole distribution. It is shown that a non-uniform liner provides a greater attenuation than a uniform liner with the same average impedance if it is 'well-matched' to the sound field, that is, if it has higher impedance at the peaks and lower at the nodes of the standing modes.

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Section: Wave Field Due To Initial Conditions or Sourcesmentioning

confidence: 99%

Section: L'hôpital Rule For Simple or Multiple Resonancementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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On Sound Generation in Cylindrical Flow Ducts with Non-Uniform Wall Impedance

Campos

Oliveira

2013

International Journal of Aeroacoustics

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“…In a cylindrical nozzle noise can be absorbed in its interior by vortical flow [1][2][3][4][5][6][7][8][9][10] and at the walls by acoustic liners, which may have uniform [11][12][13][14][15][16] or non-uniform [17][18][19][20][21][22][23][24] impedances. The sound field received by an observer in the farfield is determined by radiation out of the open end of the nozzle [25][26][27][28][29][30][31][32] or inlet of a fan [33,34]. In the case of nozzle there is a refraction effect which can be represented either by a vortex sheet [35] or an irregular shear layer [1,2] issuing from the lip.…”

Section: Introductionmentioning

confidence: 99%