膜态沸腾阶段球体入水空泡及流体动力特性

Cavity and Hydrodynamic Characteristics of Sphere Entering into Water during Film Boiling

基于高速摄像实验方法,对膜态沸腾阶段球体、球体为室温时的亲水性表面球体和超疏水性表面球体垂直入水过程进行拍摄,得到入水空泡演化图像,通过对图像进行处理得到球体入水深度变化曲线。基于计算流体力学方法,采用流体体积多相流模型、耦合蒸发-冷凝相变模型,对球体入水过程进行数值仿真,仿真结果与实验结果具有较好一致性。膜态沸腾阶段球体入水过程中空泡与流体动力特性的研究结果表明:膜态沸腾阶段球体入水可以产生与超疏水性表面球体类似的光滑空泡;超疏水性表面球体表面与空泡壁面的接触线位于球体中心略偏上位置,膜态沸腾阶段球体底部与水之间存在一层水蒸汽膜,空泡壁面与球体表面不发生接触,球体附近空泡直径相对较大;当入水较浅时亲水性表面球体阻力系数相对较大,当入水较深时超疏水性表面球体和膜态沸腾阶段球体阻力系数相对较大。

The cavitation evolutions in water entry processes of sphere during film boiling and the hydrophilic and superhydrophobic room temperature spheres were recorded using a high-speed video camera.The curve of water entry depth is obtained by image processing. Based on computational fluid dynamics method,the volume of fluid（ VOF） multiphase flow model and evaporation-condensation model are used to simulate the water entry process of sphere. The numerical results are in good agreement with the experimental results. The results show that the film boiling sphere can produce the same smooth cavitation as the superhydrophobic sphere does. The line of contact between the superhydrophobic sphere surface and the cavity wall is slightly above the center of the sphere. A vapor layer exists between the bottom of film boiling sphere and the water,the cavity wall does not contact with the surface of sphere,and the cavity diameter near the sphere is relatively large. When the water is shallow,the drag coefficient of hydrophilic sphere is relatively large; and when the water is deep,the drag coefficients of superhydrophobic and film boiling spheres are relatively large.