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A Theoretical Study of the Effect of Forward Speed on the Free-space Sound-pressure Field Around Propellers

出版	National Advisory Committee for Aeronautics, 1954
URL	http://books.google.com.hk/books?id=816zSgAACAAJ&hl=&source=gbs_api

註釋The sound-pressure field of a rotating propeller in forward flight in free space is analyzed by replacing the normal-pressure distribution over the propeller associated with thrust and torque by a distribution of acoustic pressure doublets acting at the propeller disk and subject to uniform rectilinear motion. The basic element used to synthesize the field is the pressure field of a concentrated force moving uniformly at subsonic speeds, for which an expression generalizing one of Horace Lamb's for the moving and for the fixed observer. The strength of the doublet distribution is related to the thrust and torque distribution in a convenient but approximate way. The sound field is expressed by integration over the propeller disk, and also by integration over an effective ring, and is given both for the near pressure field and, in a simpler form, for the far field. Known results for the zero-forward-speed case present themselves in the special case for Mach number M = ). Some illustrative examples are calculated and discussed.