A novel trajectory-informed stochastic closure for near-wall deposition onset in horizontal slurry pipe flow

The critical deposition velocity in horizontal liquid–solid slurry pipe flow is conventionally associated with the onset of persistent solids deposition or bed formation, but resolving that transition directly with coupled computational fluid dynamics-discrete element method (CFD-DEM) simulations is computationally expensive. Here, we developed a novel stochastic collision-resuspension cascade model (SCRCM), a trajectory-informed reduced closure that compresses near-wall CFD-DEM statistics into a model-specific near-wall deposition-onset threshold, U⋆. Wall-normal particle motion is represented through probability-weighted continuous downward and upward transport, effective non-impulsive vertical dispersion, and intermittent upward escape events. The operational threshold is formulated as a near-wall transport-scale balance in which effective vertical dispersion enters explicitly through a dimensionless drift-dispersion weighting. Four baseline CFD-DEM states yield conditional U⋆ values of 1.161, 1.287, 1.392, and 1.482 m s−1 under the prescribed baseline velocity-scaling hypotheses. An additional dp=2.5 mm state at U=1.0 m s−1, excluded from baseline coefficient construction, provides an independent directional check: relative to the 1.5 m s−1 state, it exhibits greater near-invert occupancy, a lower mean particle height, and stronger late-time accumulation. Sensitivity analyses identify event classification, near-wall layer definition, scaling exponents, and reference state as the principal structural dependencies, while trajectory-cluster bootstrapping quantifies within-simulation sampling variability. Taken together, these results support the SCRCM as a computationally efficient, mechanistically interpretable, finite-horizon proof-of-concept for trajectory-based near-wall deposition-onset analysis and identify the additional velocity-resolved and bed-onset data required for calibration.