The Numerical Simulation Of Microbubble Drag Reduction In High-speed Ship

In the way of energy-saving ships, microbubbles drag reduction by more and more the favour of people. The research of microbubbles drag reduction in ship also attracted a large number scholars at home and abroad for the indefatigable effort. The principle of microbubbles ship can be simply explained that it injected the air (or gas) in the surface of the ship bottom to forming gas-water mixing two phase flow, it can reduce the density of turbulent boundary layer and change the fluid flow field of stateso as to reduce the friction surface basic to achieve the purpose of saving energy. The application and theory analysis of microbubbles drag reduction has not only limited in the research of the theory and experiment, but also the need to be assisted with other methods. With the development of computer, the numerical simulation, as a kind of auxiliary tool, has become a trend. Because it can be intuitive drag reduction phenomenon shows and make reasonable description of test results, still predict and provide improvement scheme.The paper analysed the basic theory and numerical analysis method of microbubbles drag reduction on the basis of the previous experimental and theoretical research, and establish the reasonable numerical calculation method and numerical model. And from 2d approximation the bottom of the ship, it analyses the relationship of the drag reduction rate and the void fraction, and draw a conclusion that the void fraction is a principal element of impacting on the drag reduction rate porosity of the relationship, the key to improve the drag reduction rate is to improve the void fraction of the ship.The simulated result of 2d approximation the bottom of the ship showed that the microbubbles injection can reduce the basic friction resistance to 85% or so; the drag reduction rate increase with the increase of jet volume and reduce with the increase of mainstream velocity. The diameter of microbubbles has little effect on the drag reduction rate; With the different air injection angles the direct injection has a better advantage in the effects of drag reduction. It is easy to see that using different forms of jet control the void fraction is a very powerful and efficient technique in increasing of the drag reduction rate.Based on the above work, I carried out numerical simulation to three-dimensional solid ship and obtained the relation among the drag reduction rate, the jet rate and Froude number. By the change analysis of the turbulent kinetic energy, turbulence dissipation rate, pressure, porosity and the drag reduction rate, the definition of the best jet rate had a basis. By simulation analysis, I got that the best jet rate whose Froude number was between 1.3 and 2.1 was about 4, and the best drag reduction rate was about 22%. The increase of turbulent momentum induced by the increase of the local viscosity around micro-bubble was a main reason to reduce turbulent friction drag, and it provided a reference for the further theoretical studies of the micro-bubble drag reduction of ships.