Two-phase flow simulation of the coolant onto simplified stator coil structure*

Stator coils of automobiles in operation generate heat and are cooled by coolant poured from above. Since the behavior characteristic of the coolant poured on the coils is not clarified yet due to its complexity, the three-dimensional two-phase flow simulation is conducted to characterize the flow. In this study, the coils are modeled with horizontal rectangular pillar arrays where the poured coolant touches down. The two-phase flows are simulated by using the phase-field lattice Boltzmann method of which the solid-fluid boundary is improved. The effects of the governing parameters on the coolant behavior, such as the physical properties of the working fluid, the wettability, and the gap between the pillars are investigated. The results show that the coolant tends to spread across the pillars because of its high viscosity. Moreover, the liquid spreads extensively when the contact angle is small. It is found that the smaller gaps are preferable for spreading over a wider area. However, in case of too narrow gaps, the discharge efficiency decreased. We also conducted the simulation for the flow into the stacked pillars, and found the wetting area of the inner pillars becomes larger than that of the exposed pillars due to the capillary force.