Abstract
One of the major noise producing mechanisms in a fan stage for a turbofan engine is the interaction of the rotor wakes with the downstream stator vanes. Previous work has indicated that the rotor tip flow irregularities (vortices and velocity defects) may be as large or larger a source of blade passage tone noise as the usually considered mean rotor wake. Flow was removed between the rotor and stator of an existing fan stage by an outer wall slot and noise measurements were made to investigate the rotor tip flow irregularity‐stator interaction as a noise source. Farfield noise data taken in an inlet arc showed little tone noise reduction with flow removal, probably the result of rotor‐stator interaction noise not propagating upstream through the rotor. In‐duct measurements behind the fan stator did show noise reduction with flow removal and proportionally more reduction occurred with the first increment of flow removal than with subsequent amounts. Since the tip flow irregularities were assumedly removed with the first increment of flow, the duct measurements indicate that the tip flow irregularity‐stator interaction is probably as large a noise producing mechanism as the normally considered rotor wake‐stator interaction.
Published Version
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