A comparison is made between the conventional compact source prediction for airfoil sound radiation and the rigorous prediction based on distributed sources along the airfoil chord. The theoretical analysis performed is for a single airfoil and cascaded airfoils immersed in a sinusoidally varying convected gust field. The pressure field around a single airfoil in supersonic gust flows is also studied. In subsonic flows the phase change of unsteady lift along the chord of a single airfoil reduces the sound radiation significantly in the upstream direction and increases the downstream radiation compared to the compact source prediction. In supersonic flows the compact source prediction gives substantial error in the region just behind the Mach wedge originating from the leading edge, while it approaches the noncompact source results far downstream from the airfoil. In the case of cascaded airfoils the compact source prediction overestimates the upstream radiation by as much as 20 dB depending on frequency and interblade phase.
Noncompact source effect on the prediction of tone noise from a fan rotor
American Institute of Aeronautics and Astronautics, Aero-Acoustics Conference ; 1975 ; Hampton, VA
1975-03-01
Conference paper
No indication
English
Contra-Rotating Open Rotor Tone Noise Prediction
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