Numerical Investigation of the Geometrical Design of a 1 kN Paraffin-Fueled Hybrid Rocket Motor

Since 2010, experimental work has been done with a lab-scale 1 kN paraffin-fueled Hybrid Rocket Motor at Université Libre de Bruxelles (ULB-HRM). The motor uses liquid N₂ O as oxidizer and solid paraffin as fuel. To expand the research, a single-phase numerical model of the motor has been developed recently, in 2020. Meanwhile, this model has been improved by including liquid oxidizer spray droplets and entrained fuel droplets in the flow, the latter which is a typical phenomenon in HRMs that use a liquefying fuel such as paraffin. In this paper, a short summary of the most recent two-phase CFD model is provided, followed by a first parametric study of the geometry of the ULB-HRM. It is demonstrated how the lengths of the pre-and post-combustion chamber have an impact on the flowfield, the chamber pressure, and the thrust. It is shown that the extension of both the pre-and post-combustion chamber leads to an increased chamber pressure and thrust. However, for the pre-combustion chamber, these performance parameters stagnate when the extension is more than 50%. The conical nozzle which is installed on the ULB-HRM is under investigation as well. The impact on the thrust of the nozzle half angle and nozzle expansion area ratio is demonstrated. It is shown numerically that the design of the existing nozzle is adequate, within the limiting fact that its shape is conical. Future work includes the numerical design of a minimum length bell-shaped nozzle.