Phase Field Modeling of Aluminum Agglomeration in Solid Composite Propellants

The agglomeration of aluminum (Al) nanopowder often causes efficiency losses during combustion and degradation of solid rocket motors during the burning of solid composite propellants (SCP). While physical experiments have provided valuable insights into Al agglomeration, the phenomenon is highly sensitive to propellant geometry and composition. As a result, numerical simulation provides a more versatile and systematic approach to exploring parameter spaces, particularly under conditions that are difficult, costly, or impractical to investigate experimentally. This work presents a computational model using phase field (PF) methods that simulates Al nanopowder agglomeration in an ammonium perchlorate/hydroxyl-terminated polybutadiene (AP/HTPB) SCP. The model is implemented in Alamo, an open-source, in-house multiphysics solver for PF simulations with block-structured adaptive mesh refinement (BSAMR). By running the model on a set of 100 packed-sphere microstructures with varying AP weight percentages (wt%) and particle sizes, the model's ability to capture the complex physics of agglomeration at the mesoscale is determined. Simulation results generally reflect the trends predicted by the pocket model, showing that Al agglomeration is more likely to occur in SCP formulations with lower AP loadings or with coarser AP particles.