Numerical Validation of a Swirl Injection Model for a Paraffin-Based Hybrid Rocket Engine

One of the main challenges of Hybrid Rocket Engines (HREs) is the low regression rate. Swirl injection has experimentally shown an improvement in the regression rate due to the increased convective heat transfer and entrainment rate in the case of liquefying fuels. In this work, a regression rate prediction model in the case of swirl injection, previously proposed by the authors, is further investigated. The model is applied to another set of experimental data, confirming a good accuracy in predicting the regression rate along the axial evolution of the grain. The simulation results are compared with a modified mass flux based on geometric swirl number for the regression rate estimation in the presence of swirl injection proposed in the literature, providing parameters in the expected ranges. A validation is then performed on experimental test cases for swirl injection in paraffin-oxygen fueled HREs, verifying the validity of the calibration procedure based on the modification of skin friction and entrainment coefficients. Finally, an estimate of the effect of grain length on the increase in regression rate is provided, based on the comparison of different experimental test cases.