The Micro-bubble Drag Resistance Technology Research For Transport Ship

As the power of main engine for transport ship is mainly used to overcome the sailing resistance, it will be a significant research project that reducing the energy consumption by reducing the sailing resistance in the field of marine engineering. The transport vessel are mainly obese types with relative slow speed, and the frictional resistance generated by the viscous fluid is a major component of ship resistance in such type of hull, so it’s an effective means to reduce the sailing resistance by reducing the frictional resistance. For the several methods that used for reducing frictional resistance at this moment, micro-bubble drag reduction has been the most promising one because of its effectiveness of comprehensive resistance, the costing of the resistance devices, difficulty of application, ocean environment protection and so on.Micro-bubble drag resistance method that used for ships has obvious effectiveness and till now, a large number of investigation has focused on the experiment and simulation aspect. The effectiveness of micro-bubble drag resistance is quite apparent from the current theoretical result. According to the relevant reference we could know that the reduction of the resistance for local wall could reach80%-90%, for whole plate could reach50%and for total resistance of the vessel could reach32%if we inject the micro-bubble to the turbulent boundary layer.This project is to investigate the bubble drag resistance technique for an eminent river-sea through cargo ship and then provide the theoretical basis for the bubble lubrication drag reduction technology of the transport ship.This paper is to investigate the drag reduction efficiency under different numbers of air nozzle, different speed, different depth of draft and different nozzle forms. The results are as the following:1) For the obese ships with relative slow speed, the frictional resistance could be reduced9%—17%if jetting is performed at the ship bottom.2) For the obese ships with relative slow speed, jetting at the ship bottom could reduce the viscous pressure resistance because it has changed the distribution of the pressure at the bottom.3) For the same jetting flow, the reducing resistance effectiveness of the multi-stage jetting (jetting simultaneously at the bow and middle of the ship)is better than the single-stage(just at the bow).4) As the increase of the flow velocity, the distribution of gas volume concentration at the bottom is also more concentrated and the drag reduction efficiency is also increased accordingly.5) As the increase of the jetting flow, the drag reduction efficiency is also increased because the increase of the flow means that it will increase the gas volume concentration and then it will increase the gas coverage area.6) As the increase of depth of the draft, the drag reduction efficiency is decreased, but this decrease trend is apparent at low speed and it’s not obvious at high speed.7) For the obese ship with deep-draft and low speed, the drag reduction effectiveness is obvious under the smaller jetting flow, if the drag reduction effectiveness is needed, if possible, what we need to do is to increase the jetting flow.8)The drag reduction effect of the seam nozzle is better than the hole nozzle und er the same speed, flow, position and area, and also the seam nozzle will reach the sat urated jet flow easier.