Accession Number : ADA095080

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

Descriptive Note : Technical memo.,

Corporate Author : PENNSYLVANIA STATE UNIV UNIVERSITY PARK APPLIED RESEARCH LAB

Personal Author(s) : Lee,C. S.

Report Date : 15 SEP 1980

Pagination or Media Count : 135

Abstract : By using distortion screens, plane (0,0) and spinning (-1,0) acoustic modes were generated in an axial flow research fan. The unsteady lift on the rotor blade and the acoustic pressure along the duct were measured simultaneously by a lift gage sensor and a flush-mounted microphone respectively. The screens were calibrated by circumferentially traversing a five-hole probe. The typical background noise of unsteady lift and acoustic pressure was well below the desired signals. A phase-locked ensemble averaging technique was used to obtain the amplitude and phase of the periodic unsteady signals. The measured acoustic pressures were decomposed into modal pressures and compared with theoretical prediction; a reasonable trend was reached, but the discrepancies were large. The unsteady lift measurements of (-1,0) mode generation agreed with predictions except near the cutoff frequency indicating a back-reaction effect of considerable magnitude. The predictions overestimated the unsteady lift for the condition of 'aerodynamic resonance' when the plane wave was generated. (Author)

Descriptors :   *MATHEMATICAL MODELS, *FAN BLADES, *NOISE REDUCTION, *JET ENGINE NOISE, *AXIAL FLOW FANS, EXPERIMENTAL DATA, MATHEMATICAL PREDICTION, DUCTS, PRESSURE, ACOUSTICS, LIFT, AIRCRAFT NOISE.

Subject Categories : NUMERICAL MATHEMATICS
      ACOUSTICS
      JET AND GAS TURBINE ENGINES

Distribution Statement : APPROVED FOR PUBLIC RELEASE

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