77-09: The Sound of Low-Speed Fans

A general view of reported studies and prediction techniques for cooling tower noise is given. Fan noise generation is discussed with respect to the control of low to mid-frequency noise from mechanical draft cooling towers. An exploratory aerodynamic analysis of fan noise generation is provided leading to empirical relationships for trailing-edge turbulent boundary layer noise, a major noise source in propeller fans. Aeroacoustics means for reducing the sound power output of a fan are discussed.