Estimation of surface geometry on combustion characteristics of AP/HTPB propellant under rapid depressurization

The 2D sandwich model serves as a potent tool in exploring the influence of surface geometry on the combustion attributes of Ammonium perchlorate/Hydroxyl-terminated polybutadiene (AP/HTPB) propellant under rapid pressure decay. The thickness of the sandwich propellant is derived from slicing the 3D random particle packing, an approach that enables a more effective examination of the micro-flame structure. Comparative analysis of the predicted burning characteristics has been performed with experimental studies. The findings demonstrate a reasonable agreement, thereby validating the precision and soundness of the model. Based on the typical rapid depressurization environment of solid rocket motor (initial combustion pressure is 3 MPa and the maximum depressurization rate is 1000 MPa/s). A-type (a flatter surface), B-type (AP recesses from the combustion surface), and C-type (AP protrudes from the combustion surface) propellant combustion processes are numerically simulated. Upon comparison of the evolution of gas-phase flame between 0.1 and 1 ms, it is discerned that the flame strength and form created by the three sandwich models differ significantly at the beginning stage of depressurization, with the flame structures gradually becoming harmonized over time. Conclusions are drawn by comparison extinction times: the surface geometry plays a pivotal role in the combustion process, with AP protrusion favoring combustion the most.