This paper reports on quantitative tests of passive techniques for rotor-tip noise control in low-speed axial flow fans, based on blade-tip modifications involving the addition of anti-vortex appendages as end-plates. The end-plate thickness chord-wise distribution is determined to control the chord-wise evolution of the leakage vortex rotation number. The results confirm that the new end-plate configurations provide a mechanism by which leakage vortex bursting can be avoided. As such, the modified rotors represent an effective means of passive control of vortex breakdown.

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