Propeller Noise at Low Tip Speeds
Final rept. Nov 69-Mar 1971
WYLE LABS HAMPTON VA
Pagination or Media Count:
The study comprises an analytical and experimental investigation of the vortex noise generated by low-tip speed propellers. intially, the treatment of the subject is focussed on an examination of the origins of broadband noise and the methods by which these can be analytically represented. Subsequent noise measurements on simple-design propellers indicate how the typical spectra in the Strouhal frequency range are significantly influenced by an extensive range of high order harmonics of the blade passage frequency, and a treatment of this harmonic content is included in this study report. The broadband and harmonic components of noise data, obtained from propellers with blade number and blade angle variations, have been analyzed in detail and noise prediction methods have been derived for each. It is postulated that the noise source mechanisms may be associated with unstable laminar flow separation or transition at the blade surfaces. The report also includes a set of graphical procedures by which both harmonic and random spectral details of the radiated noise can be calculated by tip Mach numbers in the range 0.2 to 0.6.