2D Axisymmetric Transient CFD Analysis of Pure Paraffin/Oxygen Hybrid Rocket Combustion: Mesh and Time-Step Verification

This paper presents a two-dimensional axisymmetric transient numerical investigation of pure paraffin combustion in a laboratory-scale hybrid rocket engine. The study focuses on establishing a baseline reacting-flow model and assessing the influence of mesh refinement under cold-flow and early reacting-flow conditions. The simulations were performed in ANSYS Fluent using the Reynolds-Averaged Navier-Stokes framework with the SST k-omega turbulence model. A simplified gas-phase combustion approach was used in which paraffin decomposition products are represented by ethylene reacting with oxygen. The model was selected to capture the main combustion features while maintaining a practical computational cost. Three mesh configurations were considered: a uniform 0.12 million-cell mesh and two biased refined meshes of 0.32 million and 0.66 million cells. For each mesh, a cold-flow simulation was first advanced up to 0.025 s. Combustion was then initiated and continued up to a total physical time of 0.050 s, corresponding to 0.025 s after ignition. The baseline 0.12 million-cell mesh was further advanced up to 0.125 s total physical time to examine the transient development of the reacting flow. The results are discussed in terms of pressure distribution, velocity acceleration, static temperature field, nozzle-flow development, oxidizer consumption, and product-species formation. The present work provides a preliminary numerical framework for pure paraffin hybrid rocket combustion and establishes a foundation for future refined-mesh reacting-flow simulations and additional fuel-formulation studies.