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Accession Number:
ADA191751
Title:
A Propeller Skew Optimization Method
Descriptive Note:
Professional paper
Corporate Author:
NAVAL OCEAN SYSTEMS CENTER SAN DIEGO CA
Report Date:
1987-11-01
Pagination or Media Count:
13.0
Abstract:
A propeller operating in the turbulent wake of an axisymmetric body with appendages encounters wake non-uniformities which result in spatial and temporal fluctuations of blade angle-of-attack. These angle-of-attack fluctuations result in unsteady blade loadings and the generation of propeller noise, and the noise sources are characterized by three types of unsteady force mechanisms a turbulence injestion b vortex shedding and c blade-rate. The first two mechanisms typically generate continuous spectrum broadband radiated noise levels while blade-rate forces generate discrete frequency noise levels at various blade-passage frequencies and harmonics. This paper will address the reduction of blade-rate noise. The hull boundary layer behind an appendage is characterized by a complex velocity field typically having velocity excesses at inner radii and velocity defects at the outer radii. This type of velocity field has a complex harmonic content distribution and its effect on blade-rate noise cannot be predicted without detailed examination of the wake and the radial distribution of propeller blade forces. The reduction of blade-rate noise and thus vehicle vibration provides the motivation for the application of skew in propeller design. Keywords Turbulence injestion, Vortex shedding, Blade passage frequencies and harmonics, Blade rate.
Distribution Statement:
APPROVED FOR PUBLIC RELEASE
