球体入水空泡动态特性

Dynamic characteristics of ball water entry cavity

为研究球体低速入水的空泡特性以及空泡的形成对球体运动特性的影响,基于独立膨胀原理对充分发展后的空泡形态建立了理论模型,采用高速相机对不同速度的球体入水过程进行拍摄,观察球体入水从没有空泡到空泡充分发展的过程,分析了空泡的形成对球体后方射流的影响以及空泡对球体的运动特性的影响,研究了空泡的动态特性.结果表明,在球体入水没有形成空泡时,球体后方的射流以水柱的形式向上溅射;在形成稳定的空泡后,在空泡表面闭合前射流向四周溅射,空泡表面闭合后射流主要向上溅射.由于球体入水速度的变化、入水空泡的形成以及入水撞击时冲击力的影响,球体的加速度变化比较复杂,球体的阻力系数受到入水空泡的影响而明显减小.用建立的空泡形态理论模型得到了入水空泡截面积随时间的变化,并与实验结果进行了对比,对比结果显示了较好的一致性,分析表明不同深度处空泡从发展到破灭的时间大致相同,深度较小处的空泡截面积较大.

To study the characteristics of low velocity ball water entry cavity and the effect of cavity on ball dynamic characteristics,a cavity was modeled based on the principle of independence of the cavity sections expansion.A high-speed video camera was used to observe the process of ball water entry at different velocities and the process of cavity formation.The effect of cavity formation on jet flow and dynamic characteristics of the ball as well as the cavity dynamic characteristics were analyzed.The results showed that the formed cavity had an great effect on the jet flow.The jet was sputtered in the form of a water column when the cavity was not formed.After the stable cavity was formed,the jet was sputtered around before the surface closure and sputtered upward after the surface closure.The ball acceleration changed complexly due to the changed of ball water entry velocity,the formation of cavity and the impact force.The drag coefficient decreased when the cavity was formed.The change of the cavity section area was obtained using the proposed cavity model,which was verified by the experiment results.The time of cavity formation at different depth has little difference and the cavity section has a larger maximum area at small depth.