Numerical Study Of Scale Effect Of Nominal Wake Field And Propeller-induced Exciting Force

The shipping market speeds up the process of giant power, large scale tonnage and high speed of civil ships; With the concept of energy efficiency design indicator (EEDI) of new ships proposed and enforced, the performance of energy conservation and emission reduction,green environmental protection and safety of ships is promoted to a new height. To pursue ship economic performance, shipping industry has higher and higher demand for ship power efficiency, the marine propeller is getting heavier and heavier load and woks in worse environment. Ship propulsion performance has become the hot topic among people in the development of shipping industry, and flow characteristic of the stern wake field and propeller exciting force are the main factors that influence the ship propulsion performance.In this study, a KCS ship and a KP505 propeller are used as main study objects.Numerical analysis of the scale effect of axial nominal wake field and propeller exciting force considersing free surface for hull-propeller system was performed by using RANS method.As for the numerical study for the scale effect of axial nominal wake field,the viscous flow fields of ship in seven different scales including full scale were numerically solved; As for the numerical calculation of propeller exciting force considersing free surface for hull-propeller system, numerical self-propelled experiments were carried out for hull-propeller system based on self-designed Smart Dummy and open freedom model.To prove the reliability of the calculation method in this paper, three grids comprising different quantities of grid cells were employed to verified grid independence first. Resistance,free surface and wake field were respectively expounded to provide a resonable support for the subsequent numerical analysis.Considering that the scale effect of wake field has not yet been resolved, the scale effect of axial nominal stern wake field of KCS was analyzed. Detailed analysis was performed on the relationship between mean axial wake fraction, wake peak and wake valley of propeller disc and Reynolds number. Smart Dummy model was available by modifying the stern shape of KCS based on local parametrization modeling method, and a specific analysis was carried out on its flow field. The numerical calculation of propeller exciting force considersing free surface for hull-propeller system was performed based on Smart Dummy model, the results demonstrated that Smart Dummy showed a great potential in predicting nominal wake field of full ship and propeller-induced hull pressure fluctuations. As for surface ship, the hull gesture change will leads to a difference in numerical results on the basis of fixed model compared with the practical situation. DFBI six-DOF motion model and DFBI Superposed Rotation model were employed to conduct numerical self-propelled calculation of KCS in open freedom condition based on overset grid technology, and the method fully take hull gesture into account. It indicated that the flow field and propeller-induced exciting force of the two models were in difference by comparing with the fixed model.