Mechanism Research On Drag Reduction Of Ship By Microbubbles

Ship drag reduction technology, which has important economic and military value, can significantly reduce fuel consumption and gas emission and improve ship's speed and endurance ability, so it has been regarded as a hotspot in the field of domestic and international shipping engineering, hydrodynamics and military technology for.many decades. In recent years, the growing of worldwide concerns on the problem of energy conservation and emission reduction especially after the Copenhagen conference makes people pay more attention to the low-carbon lifestyle. Currently high environmental indicators of the emissions from ships may propose severe challenges to the existing ship design criterion.Microbubble drag reduction technology, namely injecting micro-bubbles into a turbulent boundary layer in the bottom of ships, which can change the flow of boundary layer by means of the difference density and viscosity of water and gas, significantly reduces the frictional resistance of ships. There are a lot of model test and full scale test proved the effectiveness of this approach, therefore, this technology is considered to have broad prospect for development. Accordingly reduce the frictional resistance is very important especially for large-scale low-speed ship, to which the frictional resistance accounted for about 80% of the total resistance.Using the numerical simulation software FLUENT under some basic assumptions to calculate the frictional resistance of a slab Model is proposed in this paper by gas-liquid two-phase flow method while injecting microbubbles into the boundary layer. The influence of the inlet velocity and concentration of microbubbles to skin friction drag reduction is given by comparing and analyzing frictional resistance and skin friction coefficient of the slab sections. After the calculation of slab Model, the influence of the inlet velocity of microbubbles and microbubble diameter to skin friction drag reduction of a ship Model is discussed. Finally the following conclusions is found:increasing the inlet velocity and concentration of microbubbles and microbubble diameter within a certain range, which can increase the local volume fraction of microbubbles, leads to the local frictional resistance decrease and finally increases the drag reduction efficiency. The thickness of microbubbles layer is very thin generally in the range of twenty millimeters.By reference to a lot of experiments about skin friction drag reduction of Ship Model by injecting microbubbles into boundary layer and the calculated drag reduction of numerical simulation of a slab Model and a ship Model using the software FLUENT, a testing ship model is designed and processed. Finally a testing program, which can make microbubbles very evenly covering the bottom panel of the testing ship, is given in this paper after the selection of a viable microbubble formation device and a connection device between ship bottom and the microbubble formation device.