NUMERICAL INVESTIGATIONS INTO THE FRICTION REDUCTION BY MICROBUBBLES FOR FLAT PLATES

The two-dimensional flow on the flat plate with injected microbubbles is simulated using the software,PHOENICS (V3. 2), usually used in the CFD (Computational Fluid Dynamics). A set of formulas for K-ε turbulence model modified with the presence of microbubbles, is employed.With considering the effect of gravity, interfacial lift, interphase friction, virtual mass force and interfacial pressure on the flow with microbubbles, numerical calculations for the influence of variable air volume fracton as well as distribution,injecting speed, microbubble diameter and position of introducing microbubbles on the friction reduction are presented. Results show that the friction reduction increases with increasing volume fraction and microbubble diameter within the range of 100μm, and that the velocity in the boundary layer with microbubbles is greater than that without microbubbles. The order of magnitude and trends of the experimental skin-friction are reproduced well. The uniform free-stream speed in all cases is 4m/s, giving Reynolds number of up to 20 million.