Numerical Study on Heat Transfer Characteristics of High-Temperature Alumina Droplet Impacting Carbon–Phenolic Ablative Material

This study investigates the heat transfer characteristics of high-temperature alumina droplets impacting carbon–phenolic ablative materials in solid rocket motors using the Volume of Fluid (VOF) method. Simulations under varied droplet diameters, impact velocities, wall temperatures, and accelerations were carried out, and the simulation method was validated against experimental data. Results show that heat flux drops rapidly from 20 MW/m2 to below 5 MW/m2 after the non-dimensional time t* = 0.5, due to solidified layer formation at the droplet bottom, which shifts heat transfer from convection to conduction and increases thermal resistance. The solidified layer is thicker at the sides and thinner in the center, caused by weaker heat transfer in the thinner side regions. Acceleration is found to have a negligible influence on impact dynamics within wall temperatures of 25 °C to 1000 °C, as potential energy conversion during spreading is insignificant compared to kinetic energy. Thus, droplet–wall heat transfer dominates the process. These findings provide critical thermal boundaries for ablation modeling and improve design guidance for SRMs.