Accession Number:

ADP011117

Title:

A Modal Concept for Active Noise Control in Circular or Annular Ducts

Descriptive Note:

Corporate Author:

INSTITUT FUER ANTRIEBSTECHNIK BERLIN (GERMANY)

Report Date:

2001-06-01

Pagination or Media Count:

8.0

Abstract:

Active control of sound propagation in ducts plays an important role in many technical applications e.g. the attenuation of noise in ventilating system or in the exhaust system of combustion engines. Today many control strategies exist for the simplest case, which is the noise control in the low frequency range in ducts the lateral dimensions of which are small compared to wavelength of sound. Up to the cut-on frequency of the first higher order mode a suppression of the propagating plane sound waves is possible in a broad frequency range. The situation is more difficult when the lateral duct dimensions become large compared to the wavelength as for example in the intake section of an aircraft engine With increasing rotor speed an increasing number of acoustical modes becomes present. This means. the system comprises all increasing number of degrees of freedom. As a consequence. control of the sound field is practicable just in a narrow frequency band or even limited to discrete frequencies.

Subject Categories:

  • Fluid Mechanics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE