ABSTRACT Near‐wall treatment (boundary‐layer meshing and wall functions) is a major uncertainty in solid–liquid two‐phase CFD of suspended sediment, while condition‐dependent guidelines are scarce, leading to inaccurate near‐wall fields or costly mesh trial‐and‐error. We therefore link first‐layer height selection to particle size and flow velocity. Four uniform particle sizes (90, 125, 165, 270 μm) were simulated under multiple velocities using five first‐layer heights and three wall functions (standard, scalable, non‐equilibrium). Compared with laboratory measurements, optimal schemes were identified. The optimal first‐layer height increases with particle size: about 0.5–1 times the particle diameter for 90 and 125 μm particles, about 2 times the particle diameter for 165 μm particles, and about 3 times the particle diameter for 270 μm particles; for a fixed size, it also increases with velocity. Standard wall functions work best for small particles at high velocities, whereas non‐equilibrium wall functions suit large particles at low velocities. Linear fitting and multiple regression yield a practical procedure to choose first‐layer height and wall‐function type. The proposed guideline is readily applicable to engineering CFD of sediment‐laden flows, improving prediction reliability while reducing meshing effort and computational cost.
Zhang et al. (2026) studied this question.