Study On The Mechanism Of Drag Reduction Characteristics Of Microbubbles And Micro-grooved Surface

With the increasing international exchanges,ship transportation has become the most important material transportation channel in the world.Ship power is mainly used to overcome the resistance encountered during navigation.Therefore,the research on ship drag reduction technology is of great significance for reducing ship resistance,improving energy efficiency,and achieving the strategy of “energy saving and emission reduction” and “green ship”.Based on the basic theories of computational fluid dynamics and multiphase flow,this paper carries out related research work on the surface drag reduction and microbubble drag reduction.A numerical model of drag reduction characteristics of micro-grooved surface is established,and the accuracy of the model is improved by calibration with experimental data.On this basis,the flow characteristics near the micro-grooved surface were analyzed.The drag reduction mechanism of the micro-grooved surface was explored.The influence of the groove size and water flow velocity on the drag reduction was discussed.According to the calculation results,the design criteria of micro-groove size are proposed.In this paper,a numerical model of drag reduction characteristics of microbubbles is established.The drag reduction mechanism of smooth surface with microbubble is explored.The influence of microbubble size,air flow rate and water velocity on the drag reduction is discussed.Based on the above research,the mechanism of coupled drag reduction of micro-grooved surface and microbubbles is further developed.Under certain conditions,the microbubbles can further increase the air fraction rate near the micro-grooved surface,thereby reducing the fluid shear stress and achieving the effect of coupling drag reduction.A numerical model of a single bubble motion near the wall is established,and the sliding behavior of the bubble is analyzed.Bubbles with small volume have better adhesion properties on the micro-grooved surface which contribute to the stability of the air film.In this paper,the mechanism of drag reduction of micro-grooved surface and microbubbles is systematically and deeply studied.The research results have a good guiding significance for the application and promotion of ship drag reduction technology.