Study Of Drag Reduction With Air-film On Low-speed Full Form Ship

With the development of shipping business, the status of low speed full form ship including oil tankers, cargo ships and container ships is becoming more and more important. While the viscous resistance takes a big part in the total resistance, it's critical to find ways to decrease the viscous resistance. To respond to the stratagem of energy saving and emission reduction,micro-bubble,as an environmental and energy-saving way, shows great potential in the application,having great significance in achieving win-win including economic growth and protection of ecological environment.Experiments showed that, micro-bubble under flat can decrease the frictional resistance, and ship model experiments also confirmed that micro-bubble reduce the viscous resistance of the ship model significantly. Due to the difference between actual ship and ship model and some craftwork factors,the micro-bubble technology is not mature enough to apply in the real ships. And the relevant research on the low speed full form ship is few neither. This paper will take the river-sea ship as the object,research the distribution of micro-bubble under the ship bottom and the affect of relative parameters, in order to put forward mature measures of reducing resistance with micro-bubble and controlling micro-bubbles.This paper,adopting method of CFD, use 3D software UG to build model and use numerical software FLUENT to imitate the micro-bubble distribution in the flow field and resistance reducing effect,as well as the affect of factors including hull cavity,size of air jet,angle of air jet, air volume,.coupled with air controlling measures. After software imitation, the experiments of ship model are carried out in order to acquire a practical way to apply in the actual ship.In this paper,we can get conclusions as follows.①It will reduce the friction drag by jetting air under the bottom of the slow-speed full form ship.②The air bubble cannot cover the bottom fully when air is only jetted in the bow.Air cover more area when jetted both in the bow and the middle. ③Air bubble spreads breadth-wise seriously when the velocity of the flow is low;Higher flow velocity will prevent the air from spreading breadth-wise and make air bubble move backward along the hull bottom., which is good for reduction of the drag.④The effect of drag reduction gets better with higher jet volume. There exists an effective jet volume, which corresponds the best drag reduction.⑤Air jetting will affect ship's afloat condition,with same air volume,multistage air jetting in both bow and middle of the ship can achieve better drag reduction than single stage air jetting only in the bow.⑥When the air volume is small,the effect of the drag reduction will not change much with different jet angle.⑦With fixed air volume,an appropriate larger jet area can lead to betterair distribution.