Review of micro-bubble ship resistance reduction methods and the mechanisms that affect the skin friction on drag reduction from 1999 to 2015

In order to lower down the fuel consumption and to achieve higher speed of ship, reduction in ship resistance has been the major topic of research for a long time. The most important factor in ship resistance is skin friction resistance. Micro-bubble has been shown to be able to reduce skin friction. This micro-bubble method gives the possibility to lower the friction without any change in the present hull form of a ship. The application of the micro-bubble technique reduces the surface friction by a variation of the viscosity of the fluid around the ship and makes a modification in the structure of the turbulent boundary layer. However, not much is known about the correct size, quantity, area of coverage which can effectively form a skin friction reducing mechanism. There are many established methods, such as Venturi tube type generator, tangential water-jet and forming of dissolve air and also a chemical process, such as electrolysis, may result in bubble production [1.. The use of micro-bubble as reducing agent of drag can lead to the creation of bubbly mixture near the flow surface that can significantly advances in the understanding of the underlying physical process of drag reduction. The current applications of these techniques to surface ships are discussed