The process of spacecraft entry, deceleration, landing, and ascent requires high specific impulse, high reliability, and high-precision thrust adjustments for the power system. The new hybrid rocket motor adopts a complex-shaped grain and high-energy propellant, offering high-energy characteristics, continuously adjustable thrust, a relatively simple oxidant delivery system, and high reliability, making it an ideal power choice for the above systems. However, due to changes in the characteristic structure of the three-dimensional complex flame surface degradation process, it is difficult to accurately predict the motor performance. In this study, changes in the flow field structure and performance parameters during the operation of the cross-shaped grain hybrid rocket motor are presented using fuel surface reconstruction technology based on a dynamic mesh. The spatial distribution of the fuel surface is analyzed, and the accuracy of the model is verified via firing tests. The results show that the deviations of combustion chamber pressure and thrust are less than 0.6% and 1.7%, respectively. After the test, the deviation between the simulated port area and the CT-scanned port area is less than 3.5%. The accuracy of this model is verified in terms of the above two aspects, establishing a solid foundation for predicting the performance of future hybrid rocket motors with more complex-shaped grains.

Potassium nitrate and sorbitol (KNSB) is a promising low-cost solid propellant for aerospace, characterized by stable combustion and a low pressure exponent. However, its application is constrained by a deficiency in detailed numerical simulation studies for solid rocket motors (SRMs). This study develops a comprehensive numerical model for a KNSB SRM, incorporating dynamic mesh techniques to simulate real-time burning surface regression. Steady-state internal flow field analysis proves to be well-validated by literature data, with combustion pressure and thrust errors of 7.7% and 3.2%, respectively. Increasing oxidizer mass fraction from 57.5% to 70% leads to a significant temperature rise of 22.15%. Dynamic simulations reveal that thrust and pressure initially increase after ignition but later decline as the regressing surface reduces gas generation below the nozzle exhaust rate. Comparison with literature yields an average thrust error of 4.9%, with simulated trends matching documented behavior well. This research provides a robust reference for performance prediction and supports further development of KNSB SRMs.