Transient, oscillatory, and flickering energy output behavior in heterogeneous solid propellants: A revisit via cluster packing model calculations

This study is dedicated to elucidating the energy instability phenomena exhibited by heterogeneous ammonium perchlorate/hydroxyl-terminated polybutadiene (AP/HTPB) propellant. The microscale structural intricacies of the heterogeneous attributes are mathematically represented through a stochastic rigid circle packing model. The propellant combustion process is simulated via the semi-global kinetic method, which delineates the intricacies of the reaction mechanism. In terms of pyrolysis characteristics of the condensed phase, a temperature-dependent kinetic sub-model is employed, while the complex gas-phase reactions are modeled using the conventional multiple flame model. The transient surface evaluation is meticulously tracked by a Hamilton–Jacobi equation, sourced from the generalized level-set equations. Remarkably, the predicted average burning rates of the simulated AP/HTPB propellant closely align with experimental reference data, underscoring the model's fidelity. The transient variations in temperature, flame dynamics, gas velocity, and gas species concentrations are exhaustively analyzed. These empirical insights significantly contribute to bridging the knowledge gap in the Western scientific community, which has hitherto limited discussions on the specific combustion behaviors of AP/HTPB propellants under elevated pressures. Finally, during the comprehensive discussion of several pivotal parameters—averaged mass flux and average surface temperature—potential future research trajectories for AP/HTPB propellant combustion are proposed. This model, along with its resultant simulations, offers profound insights into combustion instabilities intrinsic to the heterogeneous structural composition of solid propellants.