Numerical prediction of the fluctuating noise source of waterjet in full scale

Abstract

Fluctuating noise sources of the full-scaled waterjet equipped on the transom of a trimaran at 18 kn are analyzed by hybrid method coupling Scale-Adaptive Simulation (SAS) of periodic pulsating pressure on blades with boundary element acoustic models (BEM) for acoustic field. Numerical self-propelled tests of the full-scaled trimaran–waterjet system using $$k - \varepsilon$$ explicit algebraic Reynolds stress turbulent model (EARSM) with rotation-curvature correction are completed to output the non-uniform inflow into waterjet. The total propulsive efficiency is predicted satisfactorily, and local flow details are reasonably reproduced. Transient simulations of the fluctuating pressure of waterjet pump with non-uniform inflow at self-propelled rotating speed reveal that: pulsating pressure of the monitoring points located at the back of the rotor and before the stator presents the most dominant second blades passing frequency (BPF) line spectrum in frequency domain to reflect the rotor–stator interaction. When 0.95 times of span is used to represent the most heaviest loading section on rotor blades, the averaged pulsating pressure coefficient at BPF per unit chord is far more smaller than that on propeller blades. The acoustic highlights of the sound intensity distribution in the pump are located in the axial region between rotor with stator at BPF and its harmonics. The most-dominated tonal noise at 2BPF is 136.2 dB, and the total sound pressure level over the range of 1 kHz is 148.8 dB with scattering effect of the hull stern involved. Comparing to the propeller with a comparative absorbed power, smaller non-uniformity of inflow and smaller pulsating pressure benefits the waterjet about 16 dB quieter noise.