서강대학교

초록 (요약문)

While underwater laser cutting has several advantages for nuclear decommissioning, there is only limited understanding on the mechanism of local dry zone (LDZ) formation due to limited visual access to the kerf and the turbidity of the bubbly flow. Due to complex multi-physics phenomena, numerical simulation is also challenging. This study analyzes the formation of the LDZ and air cavity and the supersonic flow characteristics near the cutting front for a few operation parameters (stand-off distance, nozzle total pressure, kerf width) via 3-D RANS simulations of compressible two-phase flows. For a temporal snapshot of the flow field, several complex multi-physics effects are either neglected or approximated. As the stand-off distance increases, the air cavity inside the kerf is located closer to the cutting front. Above a threshold, the wall shear stress at the cutting front decreases due to the stagnation bubble. The nozzle total pressure has a significant effect on the LDZ and produces a topological change in a specific nozzle pressure range. As the kerf width increases, the jet impinging effect decreases, and air cavity separation inside the kerf is delayed. Both air jet and water ingress enter the kerf zone more readily, which can change the LDZ significantly.