Impact of Alumina Particle Modeling on Rarefied Rocket Plumes

This study investigates the high-altitude plume generated by the solid rocket motor of the third stage of Japan Aerospace Exploration Agency’s (JAXA) M–V launch vehicle. Two modeling strategies for the alumina particles produced by such a motor are explored. In the simplified approach, the particles are homogenized within the gas phase, assuming thermal and momentum equilibrium. In the more advanced formulation, alumina particles are treated as a dispersed liquid phase using a coupled Eulerian–Eulerian framework to capture interphase drag and heat transfer. Particular attention is devoted to the discretization of the particle size distribution, employing an approach based on information theory to minimize distortion. The results demonstrate that accounting for two-phase interactions significantly alters the flow characteristics within both the nozzle and the plume. To support future hybrid Navier–Stokes/direct simulation Monte Carlo computations, rarefaction criteria from the literature are evaluated and compared across the two modeling approaches. Among them, the P-criterion introduced by Bird is found to be the least sensitive to the choice of alumina modeling. Nonetheless, the analysis reveals that omitting particle–gas interactions can lead to notable inaccuracies in rarefaction prediction.