Hydrodynamic Characteristics Analysis And Energy Saving Device Design Of POD Thruster

The ship has the largest loading capacity in the shipping industry,its navigation performance and operating cost have been widely concerned by the international community.The propulsion system of the ship not only has a significant impact on navigation performance but also is closely related to the operational economy.With the gradual improvement of modern ship performance standards,the POD thruster,as one of the new propulsion systems,has achieved great success in the commercial field due to its characteristics and outstanding performance.The propulsion type of the POD thruster is completely different from the traditional propeller.POD thruster integrates the propulsion and steering gears of the POD.It can rotate 360° to provide maximum thrust in any direction.But the existence of the POD has changed the original wake of the propeller to some extent,and the interaction between the wake and the POD affects the overall performance of the thruster.Therefore,hydrodynamic characteristics analysis and energy saving device design of POD thruster is of great significance for improving the propulsion and maneuverability of ships,and can also provide certain reference significance for the design and optimization of the POD thruster in engineering practice.Based on the FINE/Marine software,the real-scale numerical simulation of the POD thruster was carried out,focusing on the influence of the POD strut type and energy saving device to the hydrodynamic performance of thruster.The main research work and analysis results are as follows:(1)Verification of the numerical simulation method of the POD thruster's open water performance.Numerical simulations were carried out by using a POD thruster model which was jointly designed by the Ocean Engineering Research Center(OERC)of the Memorial University of Newfoundland(MUN)and the National Ocean Technology Institute(IOT)of Canada.Comparing the numerical results with the experimental results,the maximum error of the propeller torque and thrust coefficient was only 3.63% and 2.06% respectively,and the thrust force error of the POD thruster was also less than 5.5%.Therefore,the numerical simulation method used in this paper can accurately simulate the hydrodynamic performance of the POD thruster.(2)Study on hydrodynamic characteristics of POD thruster.The hydrodynamic performance of propeller and POD thruster in open water was calculated separately,their hydrodynamic characteristics and the flow field around POD were analyzed.In the range of commonly used advance coefficient(J=0.3~0.7),the influence of POD on the propeller,the influence of propeller wake on POD and the distribution of velocity and vorticity around the POD were analyzed in detail.(3)The selection of optimal strut type of the POD thruster.According to the existing POD thruster products on the market,four kinds of POD calculation models were established.Considering the four main factors of POD resistance,POD transverse force,propeller thrust and propeller torque,a mathematical model for evaluating the hydrodynamic performance of POD thruster was established by using the method of fuzzy comprehensive evaluation.And the hydrodynamic performance of four different strut types POD thruster under design condition(J=0.7)was carried out.C2 is selected as the optimal strut type.(4)Energy saving device design of the POD thruster.The POD was optimized for the purpose of recycling the rotational energy in the propeller wake around the POD.Based on a small number of existing research results and the analysis of the flow field of the POD thruster,two thrust fins were designed in the middle of the POD,a cross-shaped tail fin was designed at the tail of the POD,as the energy saving device,to investigate the influence of geometric parameters such as the length,circumferential position,initial angle of attack of the thrust fin,and the length of the tail fin on the hydrodynamic performance of the POD thruster.Finally,different combined fins schemes were designed and their hydrodynamic performance under the design condition was compared with finless POD thruster.The result shows that the propulsion efficiency of POD thruster with combined fins can be increased by 2.77% under the design conditions,and the transverse force is almost zero.