Design Of The Energy Recovering Rudder Bulb-Turbine Device After Propeller And Its Effect On The Ship Fast Performance

The propeller rotates to push the fluid backward to produce thrust,at the same time the energy loss is caused by the rotation of the fluid.Researchers have given a variety of measures to recover this part of energy.The energy recovering rudder bulb-turbine device consists of turbine blades,rudder bulb,transmission shaft,generator and variable-frequency drive.The rudder bulb is half ellipsoid,and the tail is connected to the rudder smoothly.The turbine blade is installed on the rudder bulb.The propeller wake affects the turbine blade to drive it to rotate.The head of rudder bulb rotates with the turbine blades so as to drive the generator to produce electricity,recovering the rotational energy of propeller wake.The rudder bulb-turbine device not only has the advantages of filling low pressure area,eliminating hub vortex and turbulence rear hub as a rudder bulb,but also has a smaller diameter relative to propeller,which can reduce the impact on the design of ship stern and propeller.Because it is located in the propeller wake,the impact of propeller tip vortex on the blades of turbine is avoided.This paper establishes the design model of the turbine using the propeller lifting line theory and surface panel method,and the geometry of rudder bulb is determined by calculating the influence of rudder bulb on the hydrodynamic performance of the propeller-rudder system.In order to further study the effect of rudder bulb-turbine device on ship fast performance,the ship fast prediction method is discussed,then the influence of the rudder bulb-turbine on the self-propulsion factor and the power performance of full-scale ship and the flow field characteristics of self-propelled ship model are analyzed.In order to calculate the hydrodynamic performance of propeller and propeller-rudder system of a large container ship,firstly,the CFD calculation method is used to calculate the hydrodynamic performance of the KP505 propeller,and the calculated results are in good agreement with the experimental data.By the numerical method,the open-water performance of propeller of the large container ship is calculated,and the effect of advance coefficient on the pressure distribution on surface of propeller blade is analyzed,and the velocity distribution of propeller wake on one advance coefficient is given.Through the calculation of the performance of propeller-rudder system,the effect of rudder on the hydrodynamic coefficents of propeller with the change of advance coefficient is investatged,the pressure distribution on surface of propeller blade and rudder is given,and the velocity distribution of propeller wake with rudder on one advance coefficient is also observated.To design the turbine,the preliminary step is carried out by using lifting line theory,which is modified by lifting surface theory.The hydrodynamic performance of the system is predicted by using surface panel method,and the interaction between the forward propeller and turbine is considered.An iterative calculation method is used until the hydrodynamic performance of the system converges.Through the design of turbine behind propeller of the large container ship,the influence of rotational speed and design power of turbine on hydrodynamic performance of propeller-turbine system is observed.The results show that energy saving effect of turbine behind propeller reached 4.49% at design conditions and the design results is given.A detailed study of flow between propeller and turbine is carried out by using CFD method,the result shows that the turbine is successfully designed.To obtain the geometry of rudder bulb,the effect of rudder bulb on hydrodynamic performance of propeller-rudder system is investigated.Through geometry parametric study,the best minor axis semidiameter of rudder bulb is obtained,when the energy saving effect is best up to 3.86%.By analysising the pressure distribution on surface of propeller and rudder-rudder bulb and vortisity after propeller,the energy saving principle is discussed.According to the curve of energy saving effect of rudder bulb,the size of rudder bulb of rudder bulb-turbine device is selected.The hydrodynamic performance of propeller-rudder with rudder bulb-turbine device is calculated,and the result shows that the energy saving effect firstly increases and then decreases with the increase of advance coefficient and the maximum is reached at design advance coefficient.The energy saving effect of rudder bulb-turbine device is better than single rudder bulb or turbine.The numerical methods for calculating the resistance and viscous flow field of a ship are studied in detail.Through the calculation of the international standard ship model KCS and compared the calculated results with experimental data,not only the effects of mesh on simulation of free surface and stern boundary layer grid on nominal wake at propeller disk,but also the influences of time step and free surface on the resistance calculation are investigated.The simulated velocity and pressure distribution shows quite accuracy with experimental data.Finally,resistance performance and viscous flow field of a large container ship model is calculated,the wave pattern and velocity at different cross section and pressure coefficient distribution on the hull surface are given.The calculation results of resistance performance and nominal wake at propeller disk are consistent with the experimental results,which further verify the reliability of the calculation method and lay the foundation for the following numerical simulation of the self-propelled ship model and the ship fast prediction.Through the simulation of self-propelled KCS model and comparion between simulated flow field and experimental data,the reliability of the self-propelled simulation method is verified.The 1978 ITTC standard method is used to predict the performance of KCS ship.The feasibility of the fast prediction method based on CFD method is verified by comparing with the experimental results.Then simulations of a self-propelled large container ship model with and without rudder bulb-turbine device are carried out,and fast performance is also predicted for both cases.By comparing the results,it is noted that the rudder bulb-turbine device utilizeing propeller slip stream energy to produce electricity can replace a 1200 kW generator equipped in the large container ship at designed speed,which has great economic benefits.At the end,the self-propulsion simulation result at one propeller speed of rotation is studied,and it is found: the velocity distribution at ship stern is more complex with rudder bulb-turbine device;the tangential velocities is suppressed by rudder bulb-turbine device;rudder bulb-turbine device produces favorable interference on the hull,which makes a slightly increase of pressure coefficient at the ship stern and reduction of the ship pressure drag.