Droplet wetting and flow dynamics on solid surfaces using the particle-based method with an enhanced gas–liquid–solid triple-line surface tension model

To address the substantial computational resource consumption and numerical instability in three-dimensional least squares moving particle semi-implicit (3D-LSMPS) simulations, this study conducts algorithmic innovation and model refinement. First, the 3D LSMPS method is developed, and a particle shifting technique based on Voronoi diagram is introduced, enhancing the capture accuracy and topological stability. Second, a virtual grid (VG) technique is proposed to replace explicit gas particles, which reduces computational degrees of freedom while utilizing a background grid to assist in imposing interface pressure boundaries, resolving the computational divergence caused by momentum exchange under conditions of high density and viscosity ratios. Furthermore, a modified triple-line surface tension model is incorporated to achieve stable characterization of the gas–liquid–solid contact line. The numerical reliability is first validated through a dam-break flow with obstacles and square droplet deformation in liquid, where the error is maintained below 2%. By simulating droplet deformation in gas, the enhanced triple-line surface tension model is validated with a maximum error of less than 5%. The proposed method is then applied to investigate high-density-ratio multiphase flows (density ratio up to 1:10 000 and viscosity ratio up to 1:27 778) including droplet sliding on inclined walls and wetting on fuel rod bundle surfaces. Characteristic dimensionless numbers for different fluids are identified: water (Re ≈ 8.1 × 103, We ≈ 91, Oh ≈ 0.0012, Bo ≈ 13.6), liquid lead-bismuth eutectic (LBE) (Re ≈ 5.4 × 104, We ≈ 164, Oh ≈ 2.4 × 10−4, Bo ≈ 24.5), and corium (Re ≈ 130, We ≈ 66, Oh ≈ 0.0625, Bo ≈ 9.8). Quantitative results show that LBE maintains the most uniform and continuous liquid film due to its high density and momentum, exhibiting typical ligament breakup upon detachment. In contrast, corium tends to aggregate in later stages, failing to sustain a residual surface film. Water exhibits the highest instability, characterized by intermittent film thickness and intense interface fragmentation. This study provides a reliable numerical tool for the dynamic evolution of complex multiphase interfaces.