Tone Noise Radiation from a Ducted Subsonic Fan

An analytical/computational method of computing radiated noise from ducted rotor due to inflow distortion and turbulence is presented. Analytical investigations include an appropriate description of sources, the cut-off conditions imposed on the modal propagation of the pressure waves in the annular duct, and reflections at the upstream end of the duct. Far field sound pressure levels at blade passing frequency due to acoustic radiation from a small scale low speed fan are computed. Theoretical productions are in reasonable agreement with experimental measurements.