Numerical Research Of The Effects Of Drag Reduction Of Air Craft Of The Measures Of Controlling Bubbles Escaping

Reducing ship resistance is one of the directions of developing energy-saving technologies and improving the speed of the ship, and for the study of ship hydrodynamics, reducing ship resistance has been the main theme of this subject. Microbubble drag reduction technology is developed in recent three decades, many scholars at home and abroad have done a large number of experimental and theoretical researches on the micr-bubble drag reduction , and the good drag reduction effect has been tested for the trial. The national 863 project "investigation of high speed air cavity form"is aimed at the movement characteristics of bubbles, setting about the study of theories and experiments ,excogitating a new high-speed air cavity form with good bubble stability and excellent performanceThis paper is on the basis of the experimental and theoretical researches of high-speed air cavity, further study the technical measures of improving the drag reduction rate of bubbles. In order to control air bubbles to escape and increase the volume concentration of bubbles, for a high-speed craft with Control air bubbles escaping bars in different sites. Considering the shape of the cross-sections, especially the shape of sheer-profile, this paper computing a modification hull for mirco-bubbles drag reduction, By analysing the results, to seek the technical measures of controlling air bubbles escaping on both sides of the high-speed, thus increasing the rate of frictional resistance reduction and achieving the purpose of reducing resistance.In this paper, using SIMPLEC algorithm to solve Reynolds-average flow equations, as well as the Reynolds-average two-phase flow equations with mirco-bubbles,Adopting finite-volume method for discreting equations, under the conditions without micr-bubbles, choosing standard k-εturbulence model and standard wall functions, which is favor for convergence, taking into account of gravity. For air-jetting,adopting Euler's method of mixing two-phase model and standard k-εturbulence model ,and taking the flow of bubbles as the first phase, water as the second phase, and considering the relative motion between air and bubbles. The results of numerical simulation show : although it can not increase the drag reduction rate of high speed craft, setting small-scale lognitudinal control air bubbles escaping bars at the bottom of high-speed air cavity can control bubbles escaping in the direction of both sides of the hull and also increases the friction of bubbles. The sheer profile of the modification ship form is nearly flat, so can ensure bubbles having good stability, and can increase the friction of bubbles ,thus improving the rate of drag reduction. The bilg of the modification ship is designed into a angle type and maintained a certain angle downward, so it can control the bubbles escaping in transverse direction, increasing the friction of bubbles, improving the rate of frictional resistance reduction. Adopting the modification form can obtain 37.3% frictional resistance reduction at most.