The noise emitted from turbofan engines on an aircraft under approach conditions is dominated by a subjectively unpleasant high frequency whine from the compressor. An in-duct sensor error array has been described which permits the active control of sideline radiation to be performed with nearly the same effectiveness as if the error sensors were actually located in the radiated field. One of the appeals of this technique is its simplicity since it requires only the frequency and the speed of the free stream flow as input parameters. The line arrays operate independently of each other and it is envisaged that each receiver array will be implemented off-line by an independent processor whose outputs are then sent to a main processor for real time adaptation of the secondary sources. The presence of aerodynamic boundary layers at the duct wall, or shear velocity profiles across the duct, are not anticipated to invalidate the technique. Essentially, the technique works by estimating the axial wavenumbers from a number of pressure measurements axially along the duct wall. The axial modal wavenumbers remain constant across the duct's cross sectional area since the wave trace velocities on either side of an axial mean velocity stratification down the duct must match exactly.


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    Title :

    An in-duct sensors array for the active control of sound radiated from circular flow ducts


    Additional title:

    Eine kanalinterne Sensoranordnung für die aktive Schalldämpfung des von Luftströmungskanälen runden Querschnitts ausgestrahlten Geräusches


    Contributors:
    Joseph, P. (author) / Nelson, P.A. (author) / Fisher, M.J. (author)


    Publication date :

    1996


    Size :

    6 Seiten, 3 Bilder, 6 Quellen



    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English