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This paper presents the results of a theoretical and experimental study of the correlation of fluctuating forces on rigid flow spoilers with the resulting sound radiation. A system of force transducers was developed to measure simultaneously, yet independently, the drag and lift components of the fluctuating forces on flow spoilers confined within a jet-pipe system. A direct correlation of fluctuating forces with the radiated sound was found. A theory that considered the effect of the enclosure upon the sources and the effect of pipe-end reflection was developed to predict the sound power radiated to the free field from pipe-immersed flow spoilers. Both monopole and dipole sources were treated. An increase of the dipole sound-power output by a factor of 3 for frequencies below the pipe cutoff frequency was predicted and experimentally confirmed.

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