Numerical investigation of BPF noise for flexible submarine propeller design including inertial force coupling

Constructing a low-noise propeller requires the development of an adequate noise design method for a flexible propeller. This paper introduces a method to analyze the blade passing frequency (BPF) noise of a flexible propeller with inertial force coupling and derive noise characteristics for flexible propeller design. The deformation with coupling is applied to the object propeller and validated, because it matches well with the experimental results of the pitch-and-rake deformation. The coupled mode is derived through modal analysis, and the difference from the uncoupled mode is revealed in terms of pitch deformation. Noise analysis is performed for various flow velocity conditions and validated by comparing the analysis result for simple marine propeller model with the experimental results as well as by comparing the noise change due to deformation with the experimental results. The validated noise analysis method is used to analyze the characteristics of the BPF noise at various flow velocities, and noise change due to a decrease in hydrodynamic loading by the deformation with coupling is numerically confirmed for a flexible propeller compared with a rigid propeller. The results indicate the usefulness of this noise analysis method for the design of low-noise, flexible propellers.