CFD–DEM simulation of powder flow in a continuous coaxial nozzle for laser metal deposition

This work presents a fully coupled Computational Fluid Dynamics and Discrete Element Method (CFD–DEM) simulation of powder transport in continuous coaxial Laser Metal Deposition (LMD) nozzles, implemented in Simcenter STAR-CCM+. The methodology integrates a Johnson–Kendall–Roberts (JKR) adhesive contact model via custom field functions to represent cohesive particle–wall interactions influencing residence times and temporal flow structure. A refined polyhedral mesh resolves internal channels and external jet regions while maintaining coupling stability, with physics including two-species gas mixing (argon/air), Gidaspow drag, Sommerfeld shear lift, and gravity. Validation at a representative operating point (3 L/min carrier gas, 15 L/min shielding flow, Rosin–Rammler size distribution, 4.5 g/min feed) yields spatial footprints, centerline peak acceleration of ∼ 50 m/s 2 , and a 19% exit mass-flow irregularity (2 ms moving average). The predicted mass-flow irregularity (19% vs. 16% experimental) and accelerations agree closely with measurements, confirming rebound-driven intermittency and azimuthal redistribution at distributor fins as the dominant unsteadiness sources. Conversely, the standoff underprediction (10.2 mm vs. 16 mm) is traced to unresolved exit gas expansion under the incompressible assumption and drag calibration for the particle-laden jet, defining concrete refinement priorities for predictive simulation.