Abstract: In order to reveal the drag reduction mechanism of a film boiling sphere moving underwater, mixture multiphase flow model and evaporation-condensation model are used to simulate the flow around the film boiling sphere within the range of subcritical Reynolds number based on computational fluid dynamics method. The numerically simulated resistance coefficients results are in good agreement with the experimental results in Ref.［11］. The flow characteristics around the ordinary sphere and the film boiling sphere are compared. The effect of Reynolds number on the flow characteristics around the film boiling sphere is investigated, and the drag reduction mechanism of the flow around the film boiling sphere is analyzed. The numerical results show that the no-slip boundary condition of sphere surface can be changed into the slip boundary condition of vapor film due to the presence of vapor film of film boiling sphere. It reduces the viscous force exerted to the fluid by the wall, and makes the flow separation point move to the tail of sphere and reduces the resistance of the sphere. The steam accumulates in the tail of sphere. With the increase in Reynolds number, the accumulation position moves backward, the drag coefficient becomes smaller, and the flow around the tail tends to streamline.Key

Key words: filmboilingsphere, vaporfilm, flowcharacteristic, underwatermoving, dragreductioncharacteristic