Sub-visual cavitation and acoustic modeling for ducted marine propulsor.

摘要

Performance of ducted marine propulsors is influenced by a number of parameters including tip-gap size, tip geometry, blade loading, and inflow structure. Especially, tip-leakage vortex through tip-gap builds up relatively low pressure in vortex core. Since small bubbles, or nuclei, respond to the local pressure field as they convect through the propulsor, prediction of cavitation inception requires high fidelity resolution of pressure and associated flow features such as tip-leakage vortices, axial flow within the vortex core, blade and duct boundary layers, and turbulence near and within the core. This provides the motivation for the work here.; The first part of this study is to obtain a verified and validated RANS solution for the ducted rotor P5206. The incompressible RANS code CFDSHIP-IOWA is extended for RANS simulation of a marine propulsor by adding the relative rotating coordinate system and Chimera overset grid method. The mesh interpolation code PEGASUS is used for the exchange of the flow information between the overset grids.; The second part of this study is to simulate the dynamics of sub-visual bubble cavitation and the associated hydroacoustic noise due to bubble collapse. The modified Rayleigh-Plesset equation is solved along the bubble trajectory with and without turbulence fluctuation model in RANS pressure field. The acoustic noise induced by collapsing bubble is computed from the far field form of the acoustic pressure for a spherical bubble.; RANS solutions for P5206 are verified and validated using uncertainty analysis. Verification and validation analysis is applied to both integral and point variables. The thrust and torque of a ducted marine propulsor is used as the integral variable. The vortical velocity profile in tip-leakage vortex is used as a point variable. The resulting solutions are compared with experimental data. The developed bubble dynamics model is applied to study the traveling bubble cavitation on a Schiebe headform and sub-visual cavitation for the cavitation inception cases of the marine propeller P5168 and the ducted rotor P5206.