Abstract
This study presents a time-resolved numerical analysis of burnback evolution and internal ballistic performance of hybrid rocket fuel grains with cylindrical, helical, star, and star-swirl port geometries. A geometry-coupled regression and performance framework was developed to explicitly track port evolution, incorporate smooth ignition/extinction transients, and terminate combustion at wall hit, ensuring physically realistic burn durations and thrust profiles. Compared to the cylindrical grain (peak thrust 24.4 N, burn duration 31.68 s), non-cylindrical geometries produced substantially higher thrust at the cost of reduced burn time: helical (73.1 N, 7.52 s), star (34.9 N, 18.42 s), and star-swirl (69.0 N, 13.88 s). The helical geometry achieved a regression rate approximately three times that of the cylindrical baseline, while star-swirl showed a 2.8-fold increase. Peak thrust enhancements ranged from 43% (star) to 200% (helical) relative to the cylindrical grain, with burn duration reductions of 42%–76%. The corresponding mean regression rate increases were 34% for the star and 202% for the helical grain. Helical and star-swirl geometries exhibited the highest thrust levels and chamber pressures, driven by increased burning surface area and enhanced flow interaction. These results demonstrate that fuel grain geometry provides a powerful design lever for tailoring thrust-time profiles independently of propellant chemistry. Future work will focus on additive manufacturing of the investigated fuel grains and experimental firing in a laboratory-scale hybrid rocket motor. Model validation will be conducted by comparing measured regression rates, chamber pressure histories, thrust curves, and wall-hit times against numerical predictions, enabling quantitative assessment of model accuracy and identification of geometry-dependent deviations.