Microbubble’s Coalescence And Break-up And Research On Numerical Simulation Of Microbubble Drag Reduction

Seeking resistance performance, looking for good ship shaps with low resistance and better drag reduction technology, are a perpectual work that a large number of people devoted to ships. These years, energy and environment problems have become more and more serious, and energy conservation as well as emission reduction have become a globle focus of attention. The EEDI has been brought forward. The revision of the VI by-laws of MAPOL convention has been proposed. And many other similar regulars have been raised too. All of them show that it will be strictter on ship’s energy conservation and emission reduction. Under such condition, it’s undoubtedly of great value to develop drag reduction technology of ships which can cut down the amount of energy consumption and emission.Microbubble drag reduction technology can effectively reduce the frictional resistance of sailing ships, which has been proved by experimental test and numerical research.However,the overwhelming majority of numerical researches concentrated on only one bubble diameter, assuming no shape changing, no bubble coalescence and break-up. It’s obviously against the natural phenomenon. The further mechanisms of bubble’s movement and drag reduction have not been fully uncovered.This article studied factors that effect calculation result on the basis of Eularian multiphase flow model, using limited relax factor, and considering the influence of gravity,buoyancy, drag, virtual mass and surface tension. These factors included turbulent model,meshing, lift and solution order. Following work includes the simulation of the influence of bubble diameter on calculation result, and the calcaulation of microbubble drag reduction when microbubble of different diameters injected together. This article also carried out the simulation of microbubble drag reduction with microbubbles’ coalescence and break-up, by introducing the population balance model which can simulate the process of bubbles’coalescence and breakage. The calculation results of these three different kinds of methods have been compared.Several conclusions reached as follows.Turbulence model, meshing and lift all have obvious influence on numerical result. In a certain extent,the efficience of microbubble drag reduction will increase as microbubbles’ diameter grows. Although bubbles are of diffrerent sizes produced in experimental condition, theoretically, experiment cases can be simulated by injecting bubbles of a certain diameter and the results can be relatively close. Among the three different numerical methods, the result of the simulation of drag reduction with microbubbles’ coalescence and breakage shows best agreement with the experiment result.Especially work is the analysis of the microbubble diameter distribution in the case of simulation with microbubbles’ coalescence and break-up. The work in this article is of value not only in further simulating microbubble drag reduction problem but also in studying mechanism of microbubbles’ coalescence and break-up.