In this paper, the melt jet breakup behavior are numerically studied in 3D with nonorthogonal central-moment MRT color-gradient lattice Boltzmann method, which could significantly enhance the numerical stability and accuracy when applied to flows with very high Reynolds number. Firstly, the methodology to simulate immiscible two-phase flow is validated by conducting droplet oscillation tests. Then the ability of this model to accurately predict melt jet breakup in water is validated by simulating molten Wood's metal jet breakup experiments. Meanwhile, the breakup mechanisms are clarified. For the leading edge, the breakup of the side part is due to large eddies, the main part of the leading edge starts breakup owning to Rayleigh-Taylor instability. For the jet column, small droplets and filaments are stripping due to Kelvin-Helmholtz instability, segment breakup of the jet column is owning to Rayleigh-Taylor instability. Finally, the model is employed to simulate molten corium jet breakup in water. The hydrodynamic characteristics such as jet penetration depth, jet breakup length and fragment size are analyzed in detail. It is found that the simulation results are basically consistent with the dimensionless jet breakup length predicted by Epstein et al.‘s correlation when $E_0=0.1$, but relatively shorter. RTI theory significantly overestimates mass median diameter while critical Weber number and KHI theories underestimate it.

本文采用非正交中心矩MRT颜色梯度格子Boltzmann方法对3D熔体射流的破坏行为进行了数值研究，当应用于具有很高雷诺数的流动时，可以显着提高数值稳定性和准确性。首先，通过进行液滴振动测试验证了模拟不混溶两相流的方法。然后，通过模拟熔融伍德的金属射流破碎实验，验证了该模型准确预测水中的熔体射流破碎的能力。同时，阐明了分解机制。对于前缘，侧面部分的破裂是由于大涡流造成的，由于瑞利-泰勒的不稳定性，前缘的主要部分开始破裂。对于喷射柱，开尔文-亥姆霍兹（Kelvin-Helmholtz）不稳定会导致小液滴和细丝脱落，而瑞利-泰勒（Rayleigh-Taylor）不稳定则是导致喷射柱节段破裂的原因。最后，该模型被用来模拟水中熔化的Cor射流的破裂。详细分析了射流穿透深度，射流破碎长度和碎片尺寸等流体力学特征。结果发现，仿真结果与Epstein等人的相关性预测的无因次射流破裂长度基本一致。$E_0=0.1$，但相对较短。RTI理论大大高估了质量中值直径，而关键韦伯数和KHI理论却低估了它。