开放空腔壳体入水流场结构及流体动力特征研究

基于混合介质雷诺平均Navier-Stokes方程，对开放空腔壳体垂直入水运动过程开展了数值研究，得到了压力场、速度场分布，空泡波动、闭合特征，空腔气体涨缩规律，以及流体动力变化规律，并分析了空腔结构在入水运动过程中对流场结构和流体动力的影响。结果表明:液体随气体涨缩同步进出开放端；开放端局部形成波动的压力源和周期性的压力场、速度场分布；入水空泡呈现波动形态，其扩展程度与开放端液体流速相关；空泡内形成气体漩涡，随空腔涨缩往返进出空泡，对空泡闭合具有抑制作用；流体动力呈波动变化规律，频率与气体涨缩频率一致，幅值与气体涨缩程度成正比。开放空腔结构在入水过程中空腔内气体发生涨缩运动，对流场结构和流体动力产生周期性扰动作用，在一定程度上可以减缓冲击、维持空泡及运动的稳定性。 

Flow field structure and fluid dynamic characteristics of semi-closed cylinder water-entry

Numerical simulation for the vertical water-entry process of an end-closed cylinder shell was performed based on reynolds-averaged Navier-Stokes equations. The results of pressure and velocity contours, features of cavity wave and closure, rule of mass flow rate into the cavum, and hydrodynamic change rule were achieved. The influence of air compression-expansion on flow field structure and fluid dynamics was analyzed. The results show that water flow passing the open end in and out of cavum is synchronized with air movement; fluctuant pressure source appears at the open end of shell, leading to periodic pressure and velocity distribution; the expansion diameters of different axisymmetrical cavity sections are inversely proportional to speed of water into cavum; an air vortex generates in cavity, periodically enters and discharges from cavity, and prevents cavity closing; fluid dynamics present fluctuation characteristics whose frequency is equal to that of air, and the amplitude is in proportional relationship with that of air compression-expansion. The air compression-expansion motion in the progress of water-entry by the open cavum structure produces periodic perturbation of flow field and fluid dynamics, reduces impact of water-entry, and enhances the stability of cavity and motion of the an end-closed cylinder shell.