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

Abstract

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.