Numerical prediction of propeller-induced noise in open water and ship behind conditions

Abstract

In this article, the underwater noise of non-cavitating propellers is investigated using a boundary element method (BEM) coupled with the Ffowcs Williams–Hawkings (FW–H) formulation in the presence of the hull. The propeller is mounted on the vessel with an infinite plane assumed at the design draft to consider the free surface or tunnel wall effect. The hydrodynamic BEM solves the flow field for the analysis of propeller performance, then the time-dependent surface pressures are taken as the known noise sources for the FW–H equation in the form proposed by Farassat. The hull geometry and its disturbance to the medium are considered by solving the boundary integral equations, and the half-space medium is modeled by adding an additional term to the full space Green’s function for an image body beyond the infinite plane. The propeller performance in open water condition is first investigated to validate BEM predictions against experimental measurements. Along with the overall noise patterns in the flow field, decay rates of noise with the distance from the propeller and limited influence of the linear noise terms of the FW–H equation are discussed. Afterward, the propeller-induced hull pressure fluctuations are investigated, and the time history of acoustic pressures shows reasonable agreement with experimental measurements. Direct noise from the propeller, its scattered noise by the hull, and their sums as the total noise are discussed. This study identifies the dominating noise source around the hull, which could provide a basis for the noise control strategy for a ship propulsion system.