The Numerical Simulation Of Microbubble Friction Reduction On Ship

The project of The experimental and theoretic research on friction reduction by microbubbles for high-speed ships ,supported by the National Natural Science Foundation of China(No. 19772050), aims to study the key technology of air-jetting devices and its relevant problems, theoretically predict the law of bubble diffusing in the boundary layer and calculate the friction of the hull. In this paper, numerical investigation into the friction reduction by microbubble for high-speed ships is performed.In the theoretical research part of the project, Liang zhi yong adopted the pseudo-spectral matrix method to simulate the friction reduction by microbubble on flat plates numerically; and Lin li ming used the model of IPSA (Inter-Phase Slip Algorithm) provided in PHOENICS to study this problem. Based on Lin li ming' s research, this paper discuses the friction reduction by microbubble on a plat-bottom ship. The outline of the ship is protracted through the AutoCAD software, and inserted into the PHOENICS software; concerning the velocity profiles in boundary layer, the treatment of wall condition is added into the theoretical model. At the end of this paper, some explanations are presented.The model of IPSA provided in PHOENICS is also adopted, a finite volume scheme is used in discretization of governing equations and upwind difference introduced in this paper. The IPSA model solves the Navier-Stokes equations of each phase with the interphase interactions between two phases of water and air, including the interphase drag forces, interphase lift forces, interphase pressure and virtual mass forces. Accounting for the impact of bubbles on the turbulence, the K-e model1581 modified with the presence of microbubbles is employed. The wall condition is obtained by solving the modified model of Chen and Kim and the boundary of free surface is approximated by rigid-wall condition in the course of numerical simulation.This paper compares the friction reduction ratio under diverse condition of different free-steam velocities and different air injection ratio. Result of numerical simulation shows that the grads of continuous phase' s velocities decreases with the presence of microbubble of which the diameter is 100//w, the profiles of air volume fraction in the boundary layers is similar to triangle or echelon, Affected by interaction among the particle, there is a saturated airfraction, within the scope of saturated air fraction, increasing the air injection ratio can accrete the friction reduction ratio, under the condition of same air injection ratio, the free-steam velocity is larger, the effect of friction reduction is worse. The results of numerical simulation are consistent with the experimental result basically.