Numerical Simulation And Noise Analysis Of Propeller Tip Vortex Cavitation

Cavitation is a complex physical phenomenon unique to liquids.For a moving ship,the propeller induced cavitation is nearly inevitable.The cavitation phenomenon has a great negative impact on the propulsion efficiency of the propeller.At the same time,the tip vortex cavitation significantly increases the stern vibration and propeller noise by stimulating the stern.While so far,research on the mechanism of cavitation and tip vortex cavitation has not been sufficient,especially in numerical research.In this thesis,the effects of cavitation on the hydrodynamic performance,excitation force and noise characteristics of propellers are studied by numerical simulation of propeller cavitation and tip vortex cavitation.The numerical simulation of the tip vortex cavitation phenomenon was the focus and difficulty of the thesis.The CFD software FLUENT was used to calculate the flow and noise of the propeller.After calculating the tip vortex leakage angle and orientation on the numerical propeller openwater test,the mesh of the tip vortex region was refined,and then the Zwart-Gerber-Belamri cavitation model was used to simulate the propeller cavitation and tip vortex cavitation.The cavitation simulation of the propeller in the uniform flow parallel with the axis was first carried out for steady state.After comparing the results from meshes with and without refinement on the tip vortex region,it is proved that the application of mesh refinement can be more effective on simulating tip vortex cavitation.The cavitation simulation of the propeller in the oblique flow was then carried out for unsteady state by using the two turbulence simulation methods of RANS and DDES respectively.The results of cavitation patterns and pressure pulsation were compared to show that the DDES method has some advantages over the RANS method.Finally,the influence of propeller cavitation on propeller noise characteristics was studied.Based on the FW-H acoustic model,the propeller induced sound pressure pulsation was explored based on the successful simulation of the propeller induced pressure pulsation in the unsteady state.The obtained sound pressure results were compared with the pressure pulsation results obtained by the flow field simulation.It was concluded that the use of FW-H acoustic model can reasonably simulate the peak of the propeller-induced sound pressure.However,due to the "distortion" of the sound pressure results in the near-field region of the source surface,the influence of cavitation on the noise cannot be accurately obtained by FW-H model.Besides,the axial and circumferential azimuth characteristics of the propeller-induced noise were analyzed.By comparing the noise results with and without cavitation,it was concluded that cavitation not only affects the amplitude of radial noise on the wake flow of the propeller,but also changes its directional characteristics.In this thesis,the CFD method was used to successfully simulate the propeller cavitation and tip vortex cavitation.The propeller performance and radiation noise caused by cavitation were also analyzed and evaluated as well.The results were in good agreement with the model test results,which proves the effectiveness of the numerical methods such as grid encryption and turbulence processing proposed in this thesis,which has certain reference significance for engineering applications.