Sinayoko, S and Joseph, PF and McAlpine, A (2008) *High frequency multimode radiation from ducts with flow.* 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference).

## Abstract

Multimode sound radiation from hard-walled semi-infinite ducts with uniform subsonic flow is investigated theoretically. An analytic expression, valid in the high frequency limit, is derived for the multimode directivity function in the forward arc for a general family of mode distribution functions. The multimode directivity depends on the amplitude and directivity function of each individual mode. The amplitude of each mode is expressed as a function of cut-off ratio for a uniform distribution of incoherent monopoles, a uniform distribution of incoherent axial dipoles and for equal power per mode. The modes' directivity functions are obtained analytically by applying a Lorentz transformation to the zero flow solution. The analytic formula for the multimode directivity with flow is derived assuming total transmission of power at the open-end of the duct. This formula is compared to the exact numerical result for an unflanged duct, computed utilizing a Wiener-Hopf solution. The agreement is shown to be excellent. Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Item Type: | Article |
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Subjects: | UNSPECIFIED |

Divisions: | Div A > Fluid Mechanics |

Depositing User: | Cron job |

Date Deposited: | 04 Feb 2015 23:05 |

Last Modified: | 05 Feb 2015 07:47 |

DOI: |