A new method was applied in modeling and numerical simulation in transient two-phase flow inside a diesel injector for cavitation study. The simulation was started in steady flow when the needle valve was just about to be lifted and then contined to compute unsteady flow with self-made program. User define function(UDF) provided by Fluent was used in definition of boundary condition, force analysis of needle valve and computation of its speed. The initial condition was from steady flow field then every unsteady computation was decided by former flow field. This method assured numerical simulation consistent and authentic. It is possible to simulate the whole fuel injection with injector's initial condition and get statistics of pressure and phase volume fraction distribution at any time inside an injector. Simulation results are close to experiment results and it evidences that this new modeling method is valid and reliable. Cavitation commencement, expansion and disappearance are revealed during fuel injection. This modeling method provides a new way to further study two-phase flow inside diesel injection system.
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