| Energy conservation has become a worldwide topic in face of the global energy shortage and serious environmental pollution. As the restriction of environmental problems to the development of ship industry, IMO international organizations introduced the International Convention for the Prevention of Pollution From Ships, strictly limited the emissions of NOX, sulfide, inhalable particles and CO2. Developing environmentally friendly ship and energy saving is imperative. For vessels sailing in the water, The existed measures of energy-saving emission reduction mainly include reducing ship drag, increasing fuel efficiency, raising propeller efficiency, optimizing ship type and recovering tail gas. Above all,reducing ship drag can save fuel from the fountainhead, and it is the most important problem on ship energy-saving and emissions reduction. It is a common view that microbubble drag reduction is a very effective way to reduce the ship resistance, especially for the three main types of ships, since their frictionaldrag takes a great proportion to the total resistance.Microbubbles can effectively reduce the frictional resistance of the hull surface, reduce energy consumption and save energy, so that huge economic and social benefits are produced.The main phase and hull surface has large effect on distribution, development of bubble and drag reduction, so that this paper research mainly on interaction of water, bubble and surface, break-up and coalescence of bubble and mainly factors affecting the bubble drag reduction. The simulation method of the ship and flat plate microbubble drag reduction was carried out based on Eulerian multi-phase model. The basic theory and numerical calculation method of mesh mode, break-up and coalescence model, wall lubrication force and relaxation factor of the flat plate and three-dimensional hull were studied. With nemerical result and experiment verification, a more effective theory prediction method on bubble break-up and coalescence and drag reduction was obtained. Drag reduction along the flat plate was discussed, and the distribution of micro-bubbles, the influence of break-up and coalescence to microbubble's size, volume fraction and the drag reduction rate were analyzed in this paper.The results showed that after the microbubble pumped into the domain, there is a transition section on the flat plate surface, in which the coverage of microbubbles and the drag reduction effect are very poor. After this part, the volume fraction of the microbubbles on the wall increases, so that the drag reduction effect improves. The diameter of the microbubbles increase with the condition of aggregation on the surface of the flat plate, the diameter of the microbubbles decreases with the condition of break at a certain distance from the wall.Multi-phase model, standard k-epsilon turbulence mode, luo-lehr break-up and coalescence model are used to research on the numerical simulation prediction method and the performance of the ship microbubble drag reduction on a 2200 tons cargo ship, and the wall lubrication force, the microbubble break-up and coalescence, the relationship between drag reduction and bubble distribution, aggregation, break and many other factors were also take into account. The result shows that there was a transition section where the drag reduction effect is low on the bottom of the ship, which is similar to the flat plate, the drag reduction effect improves as the increase of streamwise velocity and gas injection volume,and the microbubbles aggregate rapidly on the surface of the ship. With the increase of the gas injection volume, adding vents at the bottom of the hull can increase drag reduction effect of microbubbles, but when the gas injection volume is low, the added vents will reduce the drag reduction effect. Thus, for a ship with large design waterline, the drag reduction effect has relationship with gas injection volume, number of vents, streamwise velocity and so on. |
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