A coupling method for the transition from primary to secondary breakup of liquid in multiphase flow nozzles

A volume of fluid–discrete phase model (DPM) coupling method is proposed, integrating a local physical-based transition criterion and an adaptive information transfer mechanism. The method captures the transition from continuous liquid film to discrete droplets in the near-field primary breakup and early secondary breakup. Trigger conditions based on liquid volume fraction αl < 0.5 and droplet size dp < 3Δ convert resolved clusters into DPM particles with conservative handover of volume, velocity, and position. The DPM solver with the Kelvin–Helmholtz–Rayleigh–Taylor breakup model then handles secondary breakup. A partitioned grid strategy reduces computational cost while maintaining near-field accuracy. Experiments using high-speed imaging and phase Doppler anemometry yield a spray cone angle of 84.3° (experiment) vs 84.1° (simulation), a relative error of 0.24%, and a maximum Sauter Mean Diameter error below 8.5%, with core-region errors as low as 1.2%. The Kolmogorov–Smirnov (K–S) statistic of the size distribution is 0.08. The validated near-field results show that the method effectively reduces numerical diffusion and parameter transfer distortion during the primary-to-secondary breakup transition, providing a promising framework for near-nozzle atomization simulation, with potential industrial applicability subject to future far-field validation and multi-condition parametric studies.