Numerical Simulation Of Micro-bubble Drag Reduction For Ships Moving On Waves

With increasing concern on the issue of energy saving and emission reduction, how toeffectively reduce the ship resistance, exhaust emissions and fuel consumption, and improvethe ship fast performance and economic benefits has become an urgent problem for shipresearch workers at home and abroad. Numerous ship model tests results show that injectingmicro-bubble into the bottom of ships can change the turbulent configuration by means of thedifference density and viscosity between water and gas, can effectively reduce the shipresistance, therefore the micro-bubble drag reduction technology has broad applicationprospects. At present, for the study of ship drag reduction by micro-bubble, test is the mainmethod, numerical simulation research is still less and most of them are based on thehomogeneous equilibrium flow model, without considering interaction between water andmicro-bubble, there is a gap between mathematical model and physical model. As forconsidering waves action for ship micro-bubble reduction is much less.In this paper, numerical simulation of micro-bubble drag reduction of a flat-bottomedship model in hydrostatic was carried out. Based on the Eulerian multiphase model,considering the interaction between water and micro-bubble, universal drag model andrealizable k turbulence model was selected. In the calculation, the surface of the shipwas segmented to several parts, the influence of free surface was ignored, and ship velocityand bubble diameter was maintained. Through changing gas flux, bubble entrance slot widthand methods of injecting micro-bubble, the friction of different parts of the ship model wasstudied, and the distribution of bubble volume fraction and wall shear stress in the surface ofthe ship was analyzed, then got the law that how gas flux, bubble entrance slot width andmethods of injecting micro-bubble to effect ship micro-bubble drag reduction. By comparingand analyzing the simulated results by Eulerian model and VOF model, we discovered thatusing Eulerian model to simulate ship drag reduction by micro-bubbles is more accurate, butthere is little difference between the simulated results using the two models, in order to considerthe effect of waves on the micro-bubble drag reduction, we can use the VOF model to simulatemicro-bubble drag reduction for ships moving on waves.Under some basic study of micro-bubble drag reduction for ship moving on calm water,based on the sports domain method and VOF multiphase model，the influence of injecting micro-bubble into the boundary layer for ships navigating in waves was discussed.Three-dimensional ship model was established and the influence of free surface wasconsidered. Under some typical ratio of wave length and ship length, maintaining shipvelocity, bubble diameter and wave height, how frictional drag and total drag to change withthe gas flux changing was studied and the distribution of air volume fraction was analyzed,and then got the law of gas flux influence for micro-bubble drag reduction. Under differentratio of wavelength and ship length, studied the changing of free surface, frictional drag andtotal drag, and then got how the ratio of wavelength and ship length to effect micro-bubbledrag reduction. At last，studied the effect of wave height to micro-bubble drag reduction.