Two-Phase CFD Simulation of a 1kN Paraffin-Fueled Hybrid Rocket Motor

Hybrid Rocket Motors (HRMs) are rocket motors in which the oxidizer and fuel are stored separately and in different phases. Usually, the fuel is solid and the oxidizer is liquid or gaseous. In the case where the fuel is a liquefying fuel such as paraffin, a thin layer of melted fuel is formed at the surface of the fuel grain from which droplets are entrained during operation. In addition to these fuel droplets, oxidizer droplets are also present in the reactive flow if the injected oxidizer is liquid. For some years now, researchers at Université Libre de Bruxelles (ULB) are running tests with such a type of HRM. It is a 1 kN lab-scale test bench motor which uses a paraffin fuel with liquid N₂O as oxidizer. Usually, numerical models of this type of HRMs approximate the internal flow as a single-phase flow. In the current paper however, a two-phase 2D axisymmetric steady-state RANS numerical model of the HRM at ULB (ULBHRM) is presented. It includes the injection of liquid fuel droplets as well as liquid oxidizer droplets in the flow. This is done in a Eulerian-Lagrangian framework. The model results are evaluated by comparison with 19 experimental results. In conclusion, the two-phase model is an improvement compared to the single-phase model. A good agreement between numerical and experimental results is observed, with an average deviation of 1% for the chamber pressure, and 5% for the thrust. This shows that the model can add a predictive capacity to the ULB-HRM research in future studies.