Research On Some Noise-reduction Measures And Their Effects Of Marine Propulsions

For ships,the stealth performance is an important indicator of its vitality measurement.Under working condition,the ships will produce radiated noise,and the propulsion noise occupies a large proportion.The reduction of propulsion noise can improve the stealth performance and extend sonar detection range.Thus,it is extremely important to study the vibration and noise reduction of ship propulsions.In this paper,the noise-reduction effect of some propulsion appendages is studied.The Large Eddy Simulation(LES)method is applied to the hydrodynamic performance simulation of propulsions,and the FW-H equation is used to calculate the noise performance after the steady flow field obtained.By comparing the flow field information and noise performance of propulsions,the noise-reduction effects of propulsion appendages are analyzed.The main work of this paper is as follows:The Large Eddy Simulation(LES)method applied to hydrodynamic performance simulation is introduced.Calculation models with different mesh parameters are established,and SST K-? turbulence model is used to predict the steady hydrodynamic performance of Suboff model.With the flow field fully developed,the SST K-? model is replaced by the LES model.By respecting the effect of the mesh parameter on calculation accuracy,the meshing method with high quality is determined,and its result of wake flow distribution at the propeller disk is output.The performance prediction process and its calculation result of wake field lay the foundation for the hydrodynamic performance calculation of propulsions.The cavitation tunnel experiment and numerical simulation of propulsion systems including a rudder and a propeller with its matching PBCF are carried out.The forces from different parts are recorded,and the energy-saving effect of PBCF is analyzed.According to the experimental conditions,the Surface Panel Method(SPM)based on the velocity potential iteration and the Computational Fluid Dynamics(CFD)method based on the sliding mesh model are applied to the calculation of hydrodynamic performance and flow field distribution.After the comparison between different methods,the reliability of calculation methods is verified.The prediction method of acoustic performance based on LES method is introduced,the noise performance of NACA0018 aerofoil is calculated with the method,and the flow field can be available at the same time.The reliability of the acoustic model is checked by the experimental results,and the verified method is applied to the simulation of propulsion lateral force pulsation and noise intensity.After the observation of the flow field and Sound Pressure Level(SPL),the influence on the vortex field and the noise-reduction effect of PBCF are analyzed.Based on deceleration duct section,the hydrofoil model with infinite expansion is established.The serrated noise-reduction structure is installed at the trailing edge of the hydrofoil,and the radiation noise of hydrofoils with different serrated trailing edges is calculated.The noise-reduction mechanism of the improved duct is discussed according to the results of hydrodynamic coefficients and vortex intensity.Pump-jet propulsion is installed at the tail of the Suboff model,and structural grid is used in the whole computational domain.The hydrodynamic performance is calculated by LES method,and the calculation result is checked by the Surface Panel Method.After the duct replaced by the one with serrated trailing edge,the SPL changes at different locations are observed.Depending on the contributions of different parts to the noise performance and the vortex field changes,the noise-reduction effect of the improved duct is analyzed.The results indicate that not only the noise radiation of propulsion systems but also the noise-reduction effect is directional.The PBCF reduces the hub vortex intensity and its vortex noise of systems,which has a better noise-reduction effect along the propeller shaft.By analyzing the flow field,it is found that the circumferential correlation of the duct vortex is destroyed by serrated trailing edge,the large vortex is divided into several small ones,and the vortex diffusion is accelerated.Therefore,the low-frequency noise is reduced.Due to the larger noise contribution of the duct in the radial direction,the serrated trailing edge has a better effect in the radial direction.