This work investigates the effects of the choice of momentum diffusion operator on the evolution of multiphase fluid systems resolved with Meshless Lagrangian Methods (MLM). Specifically, the effects of a non-zero viscosity gradient at multiphase interfaces are explored. This work shows that both the typical Smoothed Particle Hydrodynamics (SPH) and Generalized Finite Difference (GFD) diffusion operators under-predict the shear divergence at multiphase interfaces. Furthermore, it was shown that larger viscosity ratios increase the significance of this behavior. A multiphase GFD scheme is proposed that makes use of a computationally efficient diffusion operator that accounts for the effects arising from the jump discontinuity in viscosity. This scheme is used to simulate a 3D bubble submerged in a heavier fluid with a density ratio of 2:1 and a dynamic viscosity ratio of 100:1. When comparing the effects of momentum diffusion operators, a discrepancy of 57.2% was observed in the bubble's ascent velocity.

翻译：本文研究了动量扩散算子的选择对使用无网格拉格朗日方法（MLM）求解的多相流体系统演化的影响。具体而言，探讨了多相界面上非零粘度梯度的影响。研究表明，典型的平滑粒子流体动力学（SPH）和广义有限差分（GFD）扩散算子均低估了多相界面的剪切散度。此外，较大粘度比会加剧这一现象的重要性。本文提出了一种多相GFD方案，该方案采用计算高效的扩散算子，充分考虑了粘度跳跃间断所产生的影响。该方案被用于模拟一个浸没在密度比为2:1、动力粘度比为100:1的较稠密流体中的三维气泡。对比不同动量扩散算子的影响时，气泡上升速度的差异达到57.2%。