Characterization of nonequilibrium heat transfer of high-Stokes-number alumina droplets based on a conservative wall deposition scheme

A conservative UGKP deposition–resuspension boundary scheme is proposed for high-Stokes-number alumina particle/droplet impingement in aluminized solid rocket motors. It preserves particle-phase conservation and alleviates the near-wall statistical bias caused by traditional trap boundaries. A mean-free-path-based wall-resolution requirement is identified for grid-independent near-wall deposition–resuspension statistics, and an algebraic wall-adjacent subcell is introduced to recover these statistics on coarser meshes. Experimental cross-validation in a converging two-phase-flow facility reveals the macroscopic deposition–reflection transition mechanism. Numerical results show that near-wall collisional relaxation reduces incident-velocity statistics and suppresses wall-mass-flux fluctuations, leading to a statistically distributed deposition criterion. Discrete deposition increases the effective wall roughness, thereby elevating the critical transition Sommerfeld number under macroscopic nonequilibrium impingement to 20-25. An equivalent contact heat-transfer coefficient conditioned on the deposition state is calibrated against measured heat flux, providing a semi-empirical closure for heat transfer under nonequilibrium particle scouring.