Accession Number : ADA124819

Title :   Investigation of the Coupling of Unsteady Lift to Low Order Acoustic Duct Modes in an Axial Flow Fan.

Descriptive Note : Master's thesis for period ending Nov 82,

Corporate Author : PENNSYLVANIA STATE UNIV UNIVERSITY PARK APPLIED RESEARCH LAB

Personal Author(s) : Cowan,James Philip

Report Date : 17 JUN 1982

Pagination or Media Count : 145

Abstract : By using flow distortion screens, the plane wave (0,0) and first higher order (-1,0) and (1,0) spinning modes were generated in a low-speed axial flow fan. The perpendicular unsteady lift force on a segment of a nine-bladed rotor and the acoustic pressure along the duct were measured simultaneously by a strain gage sensor and a flush-mounted microphone, respectively. The total pressure field downstream of the screens was measured by circumferentially traversing a Kiel probe. The typical signal-to-noise ratio was sufficiently high for the desired signal isolation with a spectrum analyzer. A phase-locked ensemble averaging technique was used to obtain amplitude and phase measurements of the periodic unsteady signals. Standing waves set up in the duct between the rotor and duct inlet seemed to cause a back-reaction effect which resulted in an increase and reduction of the unsteady lift force above and below expected levels. If these effects are taken into account, theoretical predictions coupling unsteady lift to acoustic far field pressure levels conform to measured data. Therefore, it is concluded that there is a definite coupling between unsteady lift and acoustic pressure in the duct, yet determination of an unambiguous coupling factor would require more extensive data acquisition.

Descriptors :   *LIFT, *AXIAL FLOW FANS, *ROTOR BLADES(TURBOMACHINERY), *COMPRESSOR NOISE, COUPLING(INTERACTION), SIGNAL TO NOISE RATIO, LOW VELOCITY, TAKEOFF, CALIBRATION, NOISE REDUCTION, SOUND PRESSURE, PLANE WAVES, ACOUSTIC FIELDS, SPECTRUM ANALYZERS, WAVE EQUATIONS, STANDING WAVES, DUCT INLETS, JET ENGINE NOISE, AXIAL FLOW TURBINE ROTORS.

Subject Categories : ACOUSTICS
      FLUID MECHANICS

Distribution Statement : APPROVED FOR PUBLIC RELEASE

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