A Propeller Skew Optimization Method
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.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 1987
- Accession Number
- ADA191751
Entities
People
- Thomas S. Mautner