Numerical Investigation On Hydrodynamic Performance Of Propeller Boss Cap Fins

For a long time,the shipping industry has been a high energyconsumption industry.With the deteriorating of energy shortage,environmental pollution,greenhouse effect and other issues,energy saving and emission reduction has become a hot research topic for relevant personnel in the industry.Ship hydrodynamic energy-saving devices are favored by researchers because of its simple structure design,good energysaving effect,short cycle of cost recovery and no modification of the overall structure of the ship.Among them,Propeller Boss Cap Fin(PBCF)is an energy-saving device based on eddy attenuation and drag reduction technologies,which can effectively improve the propulsion efficiency of propeller,thereby greatly reducing the energy consumption of ships.In practical application,people pay much attention to the effect of PBCF on propeller flow field and energy-saving effect.Therefore,accurate hydrodynamic performance prediction of PBCF is of great significance.At present,the research on propeller is mainly based on model experiment method.There are inherent shortcomings in model test methods,such as high cost and long cycle length.With the development of Computational Fluid Dynamics(CFD),as a new means of fluid mechanics,CFD is a computer method to simulate fluid flow.CFD can effectively predict the hydrodynamic performance of propeller and display the detailed flow field,so it is an important tool for research and design of hydrodynamic energy-saving devices.In this paper,the hydrodynamic performance of PBCF is simulated by using open source software OpenFOAM's single phase solver pimpleDyMFOAM based on sliding grid technology.Firstly,in order to verify the reliability of the solver and the sliding mesh in dealing with propeller-related problems,the numerical prediction of MP687 propeller's open water performance is carried out.Compared with the experimental results,it is found that they are in good agreement.Further,the convergence of the mesh is verified.It is found that the convergence of the computational mesh is good and the solution is illustrated.After comparing the hydrodynamic performance of the propeller before and after installing PBCF,it is found that after installing fins,the hub vorticity strength at the hub of the propeller decreases significantly,eliminating the low-pressure area of the flow field near the hub.The existence of PBCF improves the propeller's thrust and reduces torque,improving the propeller's propulsion efficiency effectively.Then the influence of four parameters is studied.They are the distance ratio between PBCF and propeller,the ratio of diameter of PBCF to propeller blade diameter,the number of blades of fins and the installation angle of fins.The numerical simulation results show that PBCF has the best energy-saving effect when the distance ratio is 0.035,the number of blades is five,and the installation angle is 30°.Then,the influence of Reynolds number on the energy-saving effect of fins is investigated.There is a critical value of Reynolds number.When the Reynolds number is lower than this critical value,the energy-saving effect of fins will increase with the increase of Reynolds number.When the Reynolds number exceeds this critical value,the energy-saving effect of fins will not change significantly with the increase of Reynolds number.After that,the difference of energy-saving effect between fins with rudder and without rudder is studied.It is found that the energy-saving effect of fins with rudder is weaker than that without rudder.Finally,the scale effect of PBCF is studied.IDDES turbulence model is applied to study the scale effect of PBCF.It is found that there are obvious scale effects on PBCF.The scale effect is mainly on the fins,while the other parts of the propeller are less affected.