Noise measured from a fan with conventional rotor blading for configurations both with and without a fan shroud plus inlet is compared with similar data for a fan with rotor blade leading edge serrations. Using the conventional fan as a reference, the test data show (1) an increase in high-frequency noise due to the serration pattern for both the shrouded and shroudless configuration, and (2) an increase in low- to middle-frequency range noise for the shroudless configuration. Possible causes for the noise increases are discussed based on results obtained from the configurations tested and on current theories in available literature.
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