Numerical Prediction of Marine Propeller Noise in Non-Uniform Inflow

A numerical study on the acoustic radiation of a propeller interacting with non-uniform inflow has been conducted. Real geometry of a marine propeller DTMB 4118 is used in the calculation, and sliding mesh technique is adopted to deal with the rotational motion of the propeller. The performance of the DES （Detached Eddy Simulation） approach at capturing the unsteady forces and moments on the propeller is compared with experiment. Far-field sound radiation is predicted by the formation 1A developed by Farassat, an integral solution of FW-H （Ffowcs Williams-Hawkings） equation in time domain. The sound pressure and directivity patterns of the propeller operating in two specific velocity distributions are discussed.

Acoustic Scattering Performance for Sources in Arbitrary Motion

In this paper,an analytical time domain formulation based on Ffowcs Williams-Hawkings(FW-H)equation is derived for the prediction of the acoustic velocity field generated by moving bodies.This provides the imposition of the Neumann boundary condition on a rigid scattering surface.In order to calculate the scattering sound pressure of the duct,a thin-body boundary element method(BEM)has been proposed.The radiate sound pressure is calculated using the acoustic analogy FW-H equation.The scattering effect of the duct wall on the propagation of the sound wave is presented using the thin-body BEM.Computational results for a pulsating sphere,dipole source,and a tail rotor verify the method.The sound pressure directivity and scattering effect are shown to demonstrate the applicability and validity of the approach.

Numerical investigation of the cavitation noise around a marine propeller focusing on the influence of ventilation

Cavitation noise around propellers has many adverse effects.It is still very limited nowadays to inhibit propeller cavitation noise in engineering.In this study,the cavitation noise around a PPTC propeller is simulated using the large eddy simulation(LES)coupled with the porous Ffowcs Williams-Hawkings(PFW-H)equation.The investigation aims to find a strategy to suppress cavitation noise and analyze the noise suppression mechanism.The predicted hydrodynamic results agree well with the experimental data and are utilized in the hydroacoustic analysis.The hydroacoustic results indicate that the pseudo-thickness noise dominates the dominant frequency component of the total cavitation noise due to the effect of cavity evolution,which is one of the reasons why the pseudo-thickness noise dominates the total cavitation noise.A method is found to weaken the cavitation noise through ventilation at the generation location of the sheet cavity(SC).It is worth noting that ventilation inhibits the generation and development of SC by changing the pressure distribution on the suction surface of the blade and pushing away the cavities around the ventilation holes.Moreover,cavity evolution noise dominates the fluid volume evolution noise under the ventilated cavitating condition.Ventilation significantly attenuates the vapor volume pulsation and thus the cavity evolution noise,which leads to a reduction in pseudo-thickness noise and total cavitation noise.The ventilation mainly reduces noises at the dominant frequency of the pseudo-thickness noise and the total cavitation noise.

Hydroacoustic analysis of open cavity subsonic flow based on multiple parameter numerical models

The prediction of the flow-induced noise level is a key issue in the fluid–dynamic acoustics. In the hydroacoustics field, the complicated feedback induced by the flow past open cavities can amplify the convection instability in the shear layer which further leads to important noise radiations. The noise consists of intense narrowband and broadband components. In this paper, the level of the noise radiated by a subsonic cavity flow is calculated by using numerical flow computations based on the large eddy simulation（LES） and by solving the Ffowcs Williams-Hawkings equation. A series of three-dimensional open cavity models with overset grids and appropriate boundary conditions are developed for the hydroacoustic numerical computation. The self-sustained oscillation characteristics of the cavity flow are investigated, together with the mechanisms of the cavity noise generation. The distinguishing features of the flow-induced noise of the underwater structure cavities are studied with respect to the parameters of the cavity models, such as the free stream velocity, the dimensions of the cavity mouth, the angle of the cavity neck, the horizontal and vertical porous cavity models and the actual submarine open cavity model with an incoming flow attack angle. It is shown that it may be feasible to reduce the flow-induced noise by appropriate optimal parameters of the underwater structure cavities.

Numerical Hydro-Acoustic Prediction of Marine Propeller Noise

A source-to-far-field computation procedure aiming at predicting the noise generated by the underwater propeller was presented. Detached eddy simulation(DES) was used to resolve the unsteady flow field,which was taken as input data as noise propagation. Far-field sound radiation was performed by means of Ffowcs Williams-Hawkings(FW-H) equation. The computation procedure was finally applied to a typical marine propeller,David Taylor Model Basin(DTMB) 4118. The sound pressure and directivity patterns of this propeller were discussed.