膜态沸腾球体水下运动减阻特性

Drag Reduction Characteristics of a Film Boiling Sphere Moving Underwater

为揭示膜态沸腾球体水下运动减阻机理,基于计算流体力学方法,采用Mixture多相流模型,耦合蒸发-冷凝相变模型,对亚临界雷诺数范围内的膜态沸腾球体绕流减阻特性进行数值仿真,得到的阻力系数与文献[11]实验结果具有较好的一致性。对比分析了普通球体与膜态沸腾球体的绕流特性,研究了雷诺数对膜态沸腾球体绕流特性的影响,分析了膜态沸腾球体绕流运动减阻机理。仿真结果表明:膜态沸腾球体蒸汽膜的存在使球体壁面的无滑移边界条件转化为蒸汽膜的滑移边界条件,减小了壁面对流体的粘滞作用,使流动分离点向尾部移动,减小了球体绕流阻力;蒸汽会在球体尾部发生堆积,随着雷诺数的增大,堆积位置向后移动,阻力系数变小,尾部流动更趋于流线型。

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.