To study factors affecting the formation and conversion of two-phase flow pattern as well as the heat transfer of piston cooling gallery, a transient visual target test bench was set up to research the oscillatory flow characteristics in the cooling gallery under idle condition of the engine. The computational fluid dynamics (CFD) was employed while dynamic mesh technology, SST k–ω turbulence model and volume of fluid (VOF) two-phase flow model were applied to simulate the flow process of piston cooling gallery so as to predict the distribution pattern of two-phase flow. Simulation results were in good agreement with that experimentally obtained. It was observed that in the reciprocating movement of the piston, the action of two-phase flow oscillation was severe, forming some unstable wave flows and slug flows. Results show that under the same pipe diameter, the increase of fluid viscosity results in the decrease of amplitude and the increase of the liquid slugs number as well as the enhancement on heat transfer effect. In addition, it was revealed that injection pressure has little effect on the two-phase flow pattern. However, when the pressure is reduced, the change of the liquid phase is weakened and the locations of flow pattern transition move towards to the behind, thus the impact on the heat transfer is also faint.
