The self noise generated by a low-speed, isolated, ducted rotor was investigated experimentally. The apparatus provided inflow conditions to the rotor that were circumferentially uniform and steady, such that the noise generated by the rotor was primarily a result of unsteady surface pressures convecting past the blade trailing-edges. The volume flow rate through the rotor was manipulated in order to vary the blade-relative incidence angle, or "blade loading." The rotor RPM was also varied in order to study the speed scaling of the radiated sound. The resulting spectra were found to exhibit a wide range of features including blade-rate tones, broadband sound, and stall noise. The broadband sound was predicted using a model based on wall pressures. The wall pressures, in turn, were measured using a microphone mounted to an airfoil, and were also modeled using an empirical spectrum for boundary layers. Both methods of predicting wall pressures were found to result in reasonable broadband noise estimates.
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