空化可压缩流动空穴溃灭激波特性研究

为深入研究空化可压缩流动中空泡/空泡团溃灭过程中激波产生、传播及其与空穴相互作用规律,本文采用数值模拟方法对空化可压缩流动空穴溃灭激波特性展开了研究.数值计算基于OpenFOAM开源程序,综合考虑蒸汽相和液相的压缩性,通过在原无相变两相可压缩求解器的控制方程中耦合模拟空化汽液相间质量交换的源项,实现了对空化流动的非定常可压缩计算.利用上述考虑汽/液相可压缩性的空化流动求解器,对周期性云状空化流动进行了数值模拟,并重点研究了空穴溃灭激波特性.结果表明:上述数值计算方法可以准确捕捉到空穴非定常演化过程及大尺度脱落空泡云团溃灭激波现象,大尺度脱落空泡云团溃灭过程分为3个阶段:(1) U型空泡团形成; (2) U型空泡团头部溃灭; (3) U型空泡团腿部溃灭.在U 型空泡团腿部溃灭瞬间,观察到激波产生,并向上游和下游传播,向上游传播的激波与空穴相互作用,导致水翼吸力面新生的附着型片状空穴回缩,直至完全溃灭.并且空穴溃灭激波存在回弹现象, 抑制了下一周期的空化发展. 

NUMERICAL SIMULATION OF SHOCK WAVE DYNAMICS IN TRANSIENT TURBULENT CAVITATING FLOWS1)

To investigate the cloud cavity collapse induced shock wave dynamics in unsteady cavitating flows,especially the shock wave formation,propagation,and the interaction between shock wave and cavity,numerical simulation is conducted to study the shock wave dynamics dominated unsteady cloud cavitating flows.The numerical method is achieved by implementing phase change model into the native pressure-based compressible two-phase flow solver,based on the open source software OpenFOAM,considering the compressibility of both liquid and vapor.The numerical results are presented for the typical shock wave dominated unsteady partial cavitating flow,characterized by low Strouhal number around a NACA66 hydrofoil at $\alpha=6$°and $\sigma=1.25$.The results show that the predicted unsteady cavity behaviors agree well with the experiments,especially the large scale cloud cavity collapse induced shock wave phenomena.The large scale cloud cavity collapse process can be depicted into three stages:(1) the formation of U-shape cloud cavity; (2) the collapse of U-shape cloud cavity head; (3) the collapse of U-shape cloud cavity legs.The shock wave is generated and emitted during the third stage and will propagate both upstream and downstream.When the shock wave propagates to the new attached cavity sheet,it will cause the attached cavity sheet collapse,and with the shock wave propagation within the cavity sheet,the attached cavity sheet is shorten until totally collapsed.Following,the shock wave rebound phenomena occurs.The shock wave propagation and rebound are responsible for the increase in cavity evolution cycle and thus the low cavitation Strouhal number.The shock wave dynamics analysis shows that the flow parameters across the shock wave front during the interaction between shock wave and cavity satisfies the 1-D shock wave relationship.