Status of Research on Propeller Noise and Its Reduction

Fundamental concepts in the theory of noise from propellers are reviewed. Comparisons between experiment and theory are given for conditions of both subsonic and supersonic tip speeds. It is shown, for example, that the trend toward increasing sound energy in the higher harmonics with increased propeller tip speed is in accord with the theory. Noise of dual rotating propellers including blade interference and the associated directional effects is also discussed, and brief mention is made of tandem and shrouded configurations. Since the existence of intense oscillating pressure fields may be of importance both from acoustical and structural considerations, the sound field near the propeller in the vicinity of the wing and fuselage is discussed. The concluding section of the paper deals with some aspects of the propeller noise problem with reference to future high powered transport type aircraft. Results of recent analytical studies of acoustical and aerodynamic aspects of this problem are summarized. The noise intensity and spectrums of some proposed designs are compared with available tentative tolerance criteria.