Research On Air Lubrication Drag Reduction Of Green Ro-Ro Ship

In the context of the global response to climate change,China has put forward the goal of achieving "carbon peak" by 2030 and "carbon neutrality" by 2060.In order to promote the realization of the dual carbon goals,the shipping industry is facing the challenge of transformation and development towards low carbon,green,and environmental protection,which has put forward new demands for energy-saving and emission-reduction technologies.Air lubrication drag reduction technology is a new type of energy-saving and emission-reduction technology that reduces ship resistance by injecting gas into the hull surface to form a covering air layer.This thesis uses numerical simulation and theoretical analysis to systematically study the air lubrication drag reduction performance of a large ro-ro ship.The research work of this thesis can provide some theoretical and design reference value for the application of air drag reduction technology on real ship engineering.The main work of this thesis is as follows:(1)Based on the gas-liquid two-phase flow theory,the CFD method was used to carry out the research on the resistance performance of ro-ro vessels and the mechanism of air drag reduction.Firstly,we analyzed the flow field distribution characteristics,the distribution characteristics and the change law of the drag component of the ro-ro ship in the process of hydrostatic navigation,then designed the air drag reduction device and scheme,and explored the air drag reduction mechanism by comparing and analyzing the dynamic change process of the physical quantity on the surface of the hull before and after the ventilation.The research results show that the ship’s sailing resistance is mainly generated by frictional resistance,which the air drag reduction technology mainly acts on,and its basic principle of drag reduction is as follows: after releasing air,a covering air layer and air-liquid mixed flow will be formed on the surface of the hull,and the fluid density will be reduced,the turbulent viscosity and dynamic viscosity will be reduced,and the Reynolds stress will be reduced,and the combined effect of these changes leads to the reduction of the resistance.Under the design speed,the maximum reduction rate of the ro-ro ship is about21.96%.(2)Based on the study of air drag reduction mechanisms,the sensitivity study of drag reduction parameters is carried out for the air drag reduction characteristics of ships.By comparing and analyzing the characteristics and evolution of air layer distribution,flow field distribution characteristics and drag component distribution and change laws under different jet Reynolds number,incoming flow Reynolds number and ship loading state and other main influencing parameters,the influence of each air drag reduction parameter on the drag reduction effect of air lubrication is explored.The research results show that: the jet Reynolds number has the greatest influence on the air drag reduction effect,and its influence mainly lies in the size of the air layer coverage area;the incoming flow Reynolds number is second,and its influence mainly lies in the transformation of the air layer distribution pattern caused by the gas-liquid inter-phase action constraint;the ship loading state has less influence on the drag reduction effect.(3)Based on the study of air drag reduction mechanism and drag reduction characteristics,the optimization study of the air drag reduction system of the ro-ro ship is carried out,focusing on the optimization of air release devices and their arrangement,and the influence of ship sailing state change and wave disturbance on air drag reduction performance is studied by the numerical wave making method to optimize the air lubrication drag reduction scheme of the ro-ro ship.The research results show that,compared with the uniform bottom air layer distribution in still water,the bottom air layer in the wave field has obvious periodic generation-shedding phenomena.The wave reduction rate of the optimized air reduction scheme can be improved by 4～5% and the air layer stability is better.(4)The presence of the air layer changes the shear force distribution on the hull surface,making the traditional method of real ship conversion no longer applicable in the jet condition.When the ship model and the real ship have an equal jet Reynolds number,the effective air layer distribution patterns of both are similar,and the new real ship conversion method can be applied.After the real ship conversion,the air drag reduction scheme designed in this thesis can reduce the effective power of the ro-ro ship by 3.73～13.41% at the design speed,and the air lubrication drag reduction effect is obvious.